integrated approach

The approach for the development of a safe system is not the simple adoption of all possible safety measures but is the consequence of a balance between the forecast risk factors and the safety measures.

With the establishment and development of international regulations, recommendations and guidelines, there is a need for a framework within which all aspects of tunnel safety are taken into account. Such a framework may contain the following principal elements:

• Safety level criteria (regulations & recommendations)
• Infrastructure and operational measures
• Socio-economic and cost-benefit criteria
• Safety assessment techniques (risk analysis and evaluation)
• Road tunnel usage
• Stage of tunnel life (planning, design, construction, commissioning, operation, refurbishment, upgrade)
• Operating experience
• Tunnel system condition.

These safety elements are described in the Chapter 5 "Elements in an integrated approach" of report 2007R07, "Integrated Approach to Road Tunnel Safety".

An integrated approach is a framework to plan, design, construct and operate a new tunnel or an upgrade to an existing tunnel, fulfilling the required safety levels at each stage of the tunnel life. This should take place in accordance with a safety plan, following the appropriate safety procedures.

Fig. 1 shows a schematic representation of a proposed integrated approach for the safety of new and in-service tunnels, comprising the elements listed above. For more information, see Chapter 6 "Conclusion" of report 2007R07 and  chapter 1 and chapter 7 of report 2016R35  which respectively address experience with the integrated approach.

General principles of tunnel safety assessment

In the past in many countries road tunnel safety to a great extent was based upon regulations and guidelines for the design, the construction and the operation of road tunnels: if the applicable prescriptions of relevant guidelines were fulfilled the tunnel was regarded as safe. These guidelines had been developed over decades and were mainly based on the experience of everyday operation, including incidents and accidents.

However, this prescriptive approach has some shortcomings which are particularly evident in incidents exceeding the range of existing operational experience:

Technical design specifications defined in guidelines are able to establish a certain level of standardization and to guarantee an adequate performance of the various technical systems; but this approach does not take into account the effectiveness of specific measures, which may be dependent on the specific conditions of an individual tunnel.

Further, even if a tunnel fulfils all regulative requirements it has a residual risk which is not obvious and not specifically addressed.

Hence, in addition to the traditional prescriptive approach, especially for complex systems a supplement is needed which specifically addresses emergency situations: the risk-based approach. Risk-based approaches allow a structured, harmonised and transparent assessment of risks for an individual tunnel, including the consideration of local conditions in terms of relevant influence factors, their interrelations and possible consequences of incidents. Moreover, risk-based approaches make it possible to propose relevant additional safety measures for the purpose of risk mitigation. Thus risk assessment can be the basis for decision-making considering cost-effectiveness in order to assure the optimum use of limited financial resources.

Therefore modern safety standards also take into account the evaluation of the effectiveness of safety measures based on risk assessment. In the European Union, for instance, the EC Directive 2004/54/EC on minimum safety requirements for road tunnels in article 13 introduces risk assessment as a practical tool for the evaluation of tunnel safety.

When performing risk assessment, it is important to realise that decision-making about risks is complex. Whereas risk analysis is a scientific process of assessment and/or quantification of probabilities and the expected consequences of identified risks, risk evaluation is a socio-political process in which judgments are made about the acceptability of those risks. Certain risk criteria have to be established to be able to evaluate the results of a risk analysis. In Chapter 4 of the technical report 2012 R23  “Current practice for risk evaluation for road tunnels” practically applicable risk evaluation strategies are presented.

Experience from past tunnel incidents

The major fire incidents of Mont Blanc, Tauern and St. Gotthard (1999 and 2001) led to an increased awareness of the possible impact of incidents in tunnels. The likelihood of escalation of incidents into major events is low, however the consequences of such incidents can be severe in terms of victims, damage to the structure and impact on the transport economy.

An international survey of major tunnel fires can be found in the technical report 05.16B « Systems and equipment for fire and smoke control in road tunnels, Table 2.1 "Serious fires accidents in road tunnels".

These catastrophes demonstrated the need for improving preparation for, as well as preventing and mitigating, tunnel incidents. This can be achieved by the provision of safe design criteria for new tunnels, as well as effective management and possible upgrading of in-service tunnels, and through improved information and better communications with tunnel users. Conclusions drawn from the enquiry following the Mont Blanc tunnel fire were that fatal consequences could be greatly reduced by:

• a more efficient organisation of operational and emergency services (harmonised, safer and more efficient emergency procedures, specifically for cross-border operation),
• more skilled personnel,
• more effective safety systems and
• greater awareness among users (car and truck drivers) on how to behave in emergency situations.

After the fire of March 24th 1999, the Mont Blanc tunnel required significant renovation before it was able to be reopened to traffic.

A detailed description of the Mont Blanc, Tauern and St. Gotthard fires including the original configuration of the tunnels, and a step-by-step guide to the incident, fire progression, and the behaviour of operators, emergency services and users, as well as the lessons to be drawn can be found in the technical report 05.16B « Systems and equipment for fire and smoke control in road tunnels. Chapter 3 "Lessons learned from recent fires". The lessons learnt are summarised in Table 3.5 of this report. Similar information is given in Routes/Roads 324 "A comparative analysis of the Mont-Blanc, Tauern and Gotthard tunnel fires" (Oct. 2004) on p 24.

However, characteristic events are fortunately rare, and may be limited to specific circumstances. Hence a systematic analysis of less severe, but more frequent incidents (collisions and fires) may provide a more representative picutre of real tunnel incidents. Appendix 5 of the technical report 2016 R35 “Experience with Significant Incidents in Road Tunnels” provides a survey of 32 randomly selected real tunnel incidents, including a short description as well as important conclusions and improvements that could be identified for specific types of incidents or tunnel systems.

Some lessons learned can be given as examples, such as:

• misbehaviour of car drivers seems to be the most common cause of tunnel incidents and may also cause problems in incident management (like impeding access of emergency services to the site of incident)
• in case of a fire drivers sometimes try to pass by the vehicle on fire to continue their ride, despite the potential danger caused by fire and smoke
• traffic management measures – such as closing of a lane (eg. by red crosses) or closing of the tunnel (by traffic lights), are often neglected if not enforced by additional means (eg. like barriers for tunnel closure)
• problems of communication between the different stakeholders involved, which may be caused by various reasons, are a key issue in incident management
• the systematic evaluation of individual incidents often contributes to the optimisation of emergency response procedures and cooperation and training of all organisations involved in incident management

However, it is not possible to give generally applicable recommendations on the basis of these findings because these may be different in dependence of the specific conditions of an individual country and an individual tunnel.

Moreover, this report presents updated statistical data on tunnel collisions (Chapter 3) and fires (Chapter 4) for many countries. The data base used for the calculations are enclosed in Appendix 3 (collisions) and Appendix 4 (fires) respectively.

Further, well-structured and reliable information on tunnel incidents is of great importance as input data for quantitative risk assessment as well as to motivate improvements in safety systems and procedures. These topics are also addressed systematically in the technical report 2016 R35 “Experience with Significant Incidents in Road Tunnels”.

Earlier reports also present a statistical census of breakdowns, collisions and fires in selected tunnels, as well as the lessons to be drawn from such events for the geometric design of the tunnel, the design of the safety equipment and the operating guidelines: 

• Technical report 05.04B "Road Safety in Tunnels"
• Technical report 05.05B « Fire and smoke control in road tunnels, Chapter 2 "Fire risk and design fires"
• Technical report 05.16B « Systems and equipment for fire and smoke control in road tunnels »: Chapter 3 "Lessons learned from recent fires"; Table 2.1 "Serious fires accidents in road tunnels", Appendix 12.2 "The Mont Blanc Tunnel renovation".

HUMAN FACTORS - TUNNEL USERS

An adequate knowledge of human factors in the context of road tunnels optimises safety by acting in the direction of the user, the tunnel design and more generally, the organisation (tunnel operating body and emergency services). The focus of this chapter is on the interaction between the tunnel system and tunnel users; additional information is provided in the page "Human factors – Operators" regarding the interaction with tunnel staff and emergency teams.

The whole tunnel system, including the organisation of tunnel management, plays an important role in tunnel safety as it determines what the tunnel users see or have to respond to, in both normal and critical situations. The nature of the traffic regulations, motorists' compliance with them and the degree to which they are enforced contribute significantly to the level of tunnel safety. The properties of the vehicles using the tunnel and the loads they carry also play an important role.

Additional measures (with respect to the minimum requirements set by the EU-Directive) could be considered when focussing on human factors and human behaviour in terms of tunnel safety. Designing for optimal human use should include assessment of human abilities and limitations and ensuring that the resulting systems and processes that involve human interaction are designed to be consistent with the human abilities and limitations that have been identified. Human abilities and limitations refer to those physical, cognitive and psychological processes that deal with perception, information processing, motivation, decision-making and taking action.

The main conclusions regarding tunnel users are that:

• the design of tunnels and their operation should take account of human factors;
• drivers need to be more aware of how they should behave in tunnels;
• a fairly long stretch of road (if possible 150 - 200 m) before the tunnel portal should not contain too many signs and signals; the necessary signs and signals at the point of entry into the tunnel should be strictly limited in number;
• the tunnel safety facilities should be easily recognisable even in normal traffic;
• alarm signals should be provided by multiple-redundant sources (e.g. public address system and variable message signs)

Designing for optimal human use should include assessment of human abilities and limitations and ensuring that the resulting systems and processes that involve human interaction are designed to be consistent with the human abilities and limitations that have been identified. Human abilities and limitations refer to those physical, cognitive and psychological processes that deal with perception, information processing, motivation, decision-making and taking action.

Technical Report 2008R17 "Human factors and road tunnel safety regarding users"  deals with this topic. It discusses observations of the behaviour of tunnel users in both normal and critical situations and, in general terms, the main human factors that influence this behaviour. The report also formulates recommended measures, additional to the minimum measures required by the EU directive.

Technical report 2011R04 "Recommendations regarding road tunnel drivers' training and information" provides recommendations to all those in charge of education and information actions. The report develops proposals for educational elements for trainers, followed by practical instructions intended for the users. The document concludes with a number of suggestions and proposals that may be useful for the delivery of training and communication activities.

The main methodological recommendations to be implemented when it is desired to pay particular attention to human factors are:

1. the need to intervene as far upstream as possible in the framework of studies,
2. the crucial importance of taking account of the work carried out in the field of integration of human and organisational factors in safety,
3. the advantages of tests to validate innovative solutions liable to be implemented.

The first point particularly concerns the design of new tunnels for which it is fundamental to intervene as far upstream as possible during the studies. This allows better account to be taken of the main factors which govern the behaviour of users in road tunnels. Among these main factors, the following can be notably mentioned:

• data related to the local context, for example, the type of traffic and thus the users concerned (locals, professionals, subscribers, etc.),
• contextual items related to the existing infrastructures upstream and downstream from the planned tunnel (route continuity logic),
• other tunnels on the route or in the neighbourhood of the tunnel,
• cross-border tunnels for which particular attention must be given to the strategies and means implemented to communicate with the users.

The second point concerns making the best use of knowledge accumulated to date in the field of general road safety, and evacuation in crisis situations in particular. This can take shape in two ways: either by referring to general lessons learnt from work carried out in this field (PIARC recommendations for example), or by involving human science specialists (psychologists, experts) in the project. The lessons learnt from real events or from the numerous exercises held in tunnels show that the technical choices made by engineers specialised in the fields of equipment and safety in tunnels are not always the most appropriate from the viewpoint of user behaviour. Involving human science specialists should be considered for the most important projects (both new tunnels and refurbishments) with particular issues (cross-border and/or particularly long tunnels, tunnels of limited dimensions, complex tunnel structures, etc.)

Independent of the possible involvement of human science specialists, it is obviously necessary to take care to ensure a wide consultation of all the actors concerned at all times. In particular, the intervention services must be closely associated with the design of the safety equipment (particular attention must be given to features provided for self-help for evacuation of users).

The third recommendation concerns the tests and trials necessary to validate innovative choices when they are considered to be desirable. When it proves to be necessary to develop innovative means, the preliminary test phases must not be neglected (indoor testing for example), nor trials on site. These trials could be usefully performed with support from experts in the field of human sciences. Their objective will be to validate the innovative measures proposed before deployment in tunnels.

As a conclusion and in general, we emphasise the need to show much pragmatism and humility in this field. A basic principle consists in preferring simple and intuitive solutions whenever possible, in line with what is currently in practice in non-confined conditions. These types of approach ensure that the measures implemented are likely to be well understood and adopted by the users.

HUMAN FACTORS - OPERATORS

An adequate knowledge of human factors in the context of road tunnels optimises safety by acting in the direction of the user, the tunnel design and more generally, the organisation (tunnel operating body and emergency services). This chapter provides information regarding the interaction with tunnel staff and emergency teams.

The term "operator" describes the body representing the owner on site and is responsible for operating the tunnel. This key player for tunnel safety works in close relation with the other players concerned (owner, public authorities, emergency services, sub contractors, other operators, users, etc.). Its main task is to manage traffic, civil engineering aspects and tunnel equipment, together with crisis and administrative management related with its missions. It plays a crucial role for optimum implementation of the tunnel safety management system.

Lessons learnt from exercises and real events have shown that the behaviour of all those in charge of operating the tunnel is a decisive factor in ensuring the safety of people during an incident.

One of the key issues regarding this topic is the appropriate reaction of the operating staff responsible for monitoring and controlling tunnels. They are the very first to be involved in road tunnel crisis management and their task is all the more difficult in that they may at any time be required to manage potentially serious events for which the probability they will happen  is extremely low. In the event of a serious incident that may require evacuation, they utilise various types of dynamic equipment that will enable them to inform and warn users in real time, whilst encouraging them to adopt the appropriate behaviour. This issue is dealt with in the technical Report 2016R06 entitled “Improving safety in road tunnels through real-time communication with users”. The report describes how to communicate information to users in normal, congested and critical conditions. It then details the various systems that could be activated in order to optimise real-time communication with users.

To react in the appropriate  manner, tunnel operators must be able to understand and control sometimes complex situations, meaning they must be very good at stress management. Specific and appropriate training is thus essential. European regulations require the personnel involved in operating tunnels to receive "appropriate initial and continuing training" (European Directive 2004/54/CE - Annex 1 § 3.1 "Operating means").

Rescue teams liable to be called on to intervene in road tunnels obviously need to have the general training required to help people and combat fires in any type of infrastructure. Tunnels are confined spaces in which a crisis or fire can very quickly render rescue operation conditions more complicated. Over and above their technical skills, firemen therefore need to be trained specifically for this type of  intervention. This training must develop their behavioural knowhow and enable them to deal appropriately with the complex situations they may be confronted with in a tunnel. This knowhow is particularly crucial for the supervisory staff who must be capable under all circumstances of adapting the operational methods initially envisaged, if needed. In order to fulfill this mission, good coordination with the tunnel staff  is critical, requiring meticulous preparation, follow-up and implementation of intervention plans, safety exercises, and training based on feedback of experience.

In the case of cross-border tunnels, attention needs to be drawn to the collaboration required between the countries concerned  in order to ensure excellent coordination between the rescue teams in crisis situations.

With respect to the tunnel operator and the rescue teams, the technical Report 2008R03 "Management of the operator-emergency teams interface in road tunnels" discusses the most relevant lessons learnt from the most serious tunnel fires of the last decades. Based on experience and these lessons learnt, the report provides information and recommendations for best practice.

Regarding these players it can be concluded that it is of utmost importance for operator's staff and emergency services:

• to organize consultation and cooperation during the tunnel design process,
• to construct contingency plans in order to prepare for tunnel user protection and fire fighting operations, and to keep these plans up-to-date,
• to organize familiarisation visits to tunnels and arrange exercises to test operational training,
• to define the measures necessary to minimise the time required to mobilise the emergency services,
• to organize post accident analysis, including events of limited importance.

Regulations regarding transport of dangerous goods through tunnels

Dangerous goods are important for industrial production as well as everyday life, and they must be transported. However, it is acknowledged that these goods may cause considerable hazards if released in a collision, on open road sections as well as in tunnels. Incidents involving dangerous goods are rare, but may result in a large number of victims and severe material and environmental damage. Special measures are needed to ensure that the transport of dangerous goods is as safe as possible. For these reasons, the transport of dangerous goods is strictly regulated in most countries.

Dangerous goods transport raises specific problems in tunnels because an incident may have even more serious consequences in the confined environment of a tunnel as compared with incidents on the open road.

From 1996 to 2001, the Organisation for Economic Co-operation and Development (OECD) and PIARC carried out an important joint research project to bring rational answers to open questions about transport of dangerous goods through tunnels: Transport of dangerous goods through road tunnels. Safety in Tunnels, Paris: OECD Publishing, 2001 ISBN 92-64-19651-X.

An international survey of regulations regarding the road transportation of dangerous goods in general and in tunnels showed that all investigated countries had consistent regulations for the transport of dangerous goods on roads in general, and that these regulations were standardised within large parts of the world. For instance, ADR (the European agreement concerning the international carriage of dangerous goods by road) is used in Europe and the Asian part of the Russian Federation. Most States in the USA and provinces in Canada follow codes in compliance with the UN Model Regulations. Australia and Japan had their own codes, but Australia has aligned with the UN system.

In contrast, the survey highlighted a variety of regulations regarding the transport of dangerous goods through tunnels. Restrictions applied in tunnels showed considerable variations between countries and even between tunnels within the same country. The inconsistency of the tunnel regulations posed problems for the organisation of dangerous goods transport and led a number of vehicles carrying dangerous goods to infringe restrictions..

As part of their joint project, OECD and PIARC made a proposal for a harmonised system of regulation. This proposal was further developed by the United Nations Economic Commission for Europe (UN ECE), then implemented in Europe in  2007 and in further revisions of the ADR.

The harmonisation is based on the assumption that in tunnels there are three major hazards which may result in numerous victims or cause serious damage to the tunnel structure, and that they can be ranked as follows in order of decreasing consequences and increasing effectiveness of mitigating measures: (a) explosions; (b) releases of toxic gas or volatile toxic liquid; (c) fires. Restriction of dangerous goods in a tunnel is made by assigning it to one of five categories which are labelled using capital letters from A to E. The principle of these categories is as follows:

Table1: List of ADR CATEGORIES

Category A	No restrictions for the transport of dangerous goods
Category B	Restriction for dangerous goods which may lead to a very large explosion
Category C	Restriction for dangerous goods which may lead to a very large explosion, a large explosion or a large toxic release
Category D	Restriction for dangerous goods which may lead to a very large explosion, a large explosion, a large toxic release or a large fire
Category E	Restriction for all dangerous goods (except five goods with very limited danger)

The decision on assigning a tunnel to one of these 5 categories can be based on risk assessment using risk assessment tools specifically developed for this kind of application.

 More information on this topic is available on the following websites:

• UN ADR 2009 documents website
• Australian ADG code website
• Canadian TDG regulations

Significant incidents in road tunnels

PIARC defines the term “incident” in the following way: An incident is an “abnormal and unplanned event (including accidents) adversely affecting tunnel operations and safety”.

 This definition of “incident” is quite broad and includes all kinds of events that may occur in a road tunnel. From a safety perspective report 2016R35 “Experience with significant incidents in road tunnels” recommends a focus on significant incidents. According to the definition in this report, significant incidents are “incidents which require special attention, because they are, or have the potential to develop into, events with serious consequences to the health or life of people, to property, to infrastructure or to the environment; or are valuable for further evaluation with respect to underlying basic risk factors. Significant incidents in particular include collisions and fires, which are addressed separately in pages Collisions and Fires respectively; the release of dangerous goods (addressed in page Hazards due to DG-Transport) is another typical example for a significant incident. However, the definition of significant incidents differs from country to country; in some countries other incidents like vehicle breakdowns or incidents that cause the closure of a tunnel are also considered as significant.

The basic understanding of these terms is illustrated in Fig.1.

Collisions

Traffic safety is a key success factor for road tunnel safety. In general, on a yearly basis, most injuries and fatalities in tunnels are related to traffic incidents that could also happen on the open road. However, since a tunnel is an enclosed space, the escalation of a collision, in terms of fire and the release of dangerous goods, could have far more serious consequences than on the open road, because more people than those directly involved in the incident can potentially be exposed to the hazards of heat, smoke, explosions or toxic gases. Moreover, the tunnel itself can contribute to the cause or the effects of a collision, for instance because of changing light conditions (the “black hole effect” when entering the tunnel) or because the tunnel wall is an “unforgiving obstacle” that can worsen the mechanical impact of a collision or impede a successful evasive manoeuvre.

To summarize:

• The prevention and mitigation of collisions in (and nearby) road tunnels needs special attention as compared to the open road;
• Assuring traffic safety in (and nearby) road tunnels is very effective to assure tunnel safety in general (although it must be noted that many, if not most, fire incidents in tunnels are vehicle related and not collision related; therefore, additional measures to assure tunnel safety remain necessary, even in the hypothetical situation that collisions are ruled out entirely).

Compared to the open road, there are several factors that may influence the probability or the effect of a collision in (and nearby) tunnels in a positive or negative way:

Positive:

• Environmental conditions are better controlled within tunnels: absence of rain, snow, ice, wind, fog, avalanches, falling rocks, etc. (but sudden changes may occur at tunnel portals).
• Tunnels can provide a shorter or safer route as compared to alternative routes (like a curvy and steep mountain pass).
• In general, there are fewer (or no) junctions, interchanges, crossroads and intersections (on the other hand, special attention is needed if they are present in or nearby a tunnel).
• Pedestrians and slow moving vehicles, (like mopeds, motorcycles, agricultural tractors or other equipment), are generally prohibited in road tunnels (or at least separated from the faster motor traffic).

Negative:

• Drivers need to perceive, analyse and understand a different driving environment.
• Especially during day-time, drivers are confronted with changing light conditions when entering and exiting the tunnel.
• Tunnels are enclosed structures with confined space that can cause, for some drivers, feelings of anxiety, and a specific behaviour of people in the event of a collision (this can be true for people both directly or indirectly involved in a collision).
• If air quality is not controlled and kept within permissible limits the behaviour of drivers can be affected.
• Proximity of stationary obstacles (like tunnel portals, road signs, ceiling, tunnel wall) may cause major disturbing effects; moreover, these obstacles can contribute to a more severe mechanical impact of a collision.
• Protective measures typical for open road sections (e.g. barriers or other energy absorption systems) are not present in all tunnels.
• Emergency lanes are often not present in road tunnels.
• The monotonous atmosphere of long tunnels may hamper the driver´s awareness.
• The tunnel conditions may cause misjudging of the horizontal and vertical alignment, as well as the safety distance from other vehicles and obstacles; moreover, the tunnel wall and ceiling can limit the viewing distance for the drivers when there are curves or gradients in the alignment.

All in all, the tunnel manager must consider traffic safety in a specific tunnel in terms of risks and measures; he must analyse and evaluate the risks (on the basis of criteria for both traffic safety and tunnel safety) and he must consider, choose and implement measures to control these risks. For new to be built tunnels, this has already to be taken into account in the planning and design phase. For existing tunnels, the tunnel manager has to evaluate the safety situation in practice (feedback from experience, learning from actual incidents or near-incidents) and take measures to improve the situation when necessary.

Of course, not all the causes, like drunk driving, mobile phone use while driving, or the defective technical condition of a vehicle, are within the circle of influence of the tunnel manager. The same goes for the effects of the collisions. However, the tunnel related causes and effects can be effective targets for the measures to reduce the risk of collisions.

More qualitative and quantitative information that is useful for the risk assessment of collisions in road tunnels can be found in the report 2016/R35 “Experience with significant incidents in road tunnels”, notably in chapter 3. In the cycle 2016-2019, WG2 (Safety) of TC D.5 (Road Tunnel Operations) is drawing up a report “Prevention and mitigation of tunnel related collisions” on the (cost) effectiveness of the various measures that are at the disposal of the tunnel manager to control the collision risks.

Other useful reports on the subject include:

• Report 2016/R16 “Lay-bys and protection against lateral obstacles in tunnels, Current Practices in Europe”;
• Report 05.04.BEN “Road safety in tunnels” (1995).

FIRES

Among the possible risks to be considered in road tunnels, vehicle fires give rise to particular concern because they are not very rare events and their consequences may be far larger underground than in the open if no appropriate measures are taken.

The discussion on tunnel fires is often dominated by the extreme events which occurred in the Mont Blanc tunnel, the Tauern tunnel and the Gotthard Tunnel. However, in reality the majority of tunnel fires are relatively small events in comparison, which nevertheless may have the potential to develop into more serious events, depending on various influencing factors. The confined space of a tunnel provides an environment in which untenable conditions may develop rapidly in case of a fire. Series of real fire tests have been performed in the context of various national and international research programs in order to confirm assumptions on fire sizes and fire behaviour; in these tests the focus again was on large scale fires with high heat release rates.

There are a few key parameters for the characterisation of a tunnel fire: The speed of fire development and the fire size are of significant importance with regard to tunnel safety. Both are influenced by the nature of the fire load, the technical conditions of the vehicles involved, the airflow conditions in the tunnel during fire development as well as the fire safety engineering design of the specific tunnel. The maximum heat release rate of a fire depends on the quantity and type of material of the fire load as well as the boundary conditions of oxygen supply, tunnel characteristics and system response etc.. Fires in personal vehicles rarely develop to high heat release rates, whereas fully developed fires in the cargo of heavy goods vehicles and pool fires of burnable liquids potentially can develop into very high heat release rates.

Two types of tunnel fires (triggered by a collision or a vehicle defect) can be distinguished with regards to their characteristics: fires resulting from vehicle defect typically start in engine, exhaust system, wheels or brakes; seldom in the load. These fires in most cases are shielded fires which are likely to develop slowly in the first phase, with progressive development in later phase resulting in a fully developed fire. This type of fire development increases the opportunity to extinguish a fire (or delay its further development) either by the use of manual fire extinguishers, fixed fire fighting systems and/or by responding fire fighters, before it is able to threaten the health and safety of people in the tunnel. Fires after collisions are often accelerated by (limited amounts) of fuel that has leaked as a result of the collision, hence the development is typically faster. Flammable liquid fires, i.e. pool fires with large amounts of flammable liquids, are extremely rare occurrences, which require a large amount of flammable liquid to be released (as a consequence of a collision or by other reasons).

In Chapter 4 of the technical report 2016 R35 «  Experience with significant incidents in road tunnels » new information on fires rates has been compiled, based on tunnel fire statistics from 12 countries around the world. The collection of data for statistical purposes requires a clear definition of events which should be considered as fires. Today there is different practise in different countries on what event is recorded as a fire and what is not; in the context of this report the defintion of the term « fire » according to the Norwegian Directorate for Civil Protection has been applied: a fire is“an unwanted or uncontrolled combustion process characterised by heat release and accompanied by smoke, flames or glowing”.

It seems that an “average tunnel” has a fire rate in the order of magnitude 5 – 15 fires per billion vehicle km. However, the scatter of the rates from tunnel to tunnel may be very significant as a number of factors may influence the recorded fire rates, for instance: tunnel design, location of the tunnel, geometry of the road, monitoring, technical standard of the vehicles, traffic regulation, speed limits, driving culture etc., hence the fire rates should be used with care and the assessment of the applicability and the modification of the basic rates required for an application for a given tunnel should be done by experts with experience in tunnel safety.

To get statistical information on type and severity of fire events is an even more complex issue. Therefore expert opinion is required in addition to the knowledge and information available from real fire incidents and real sclae fire tests. Based on recordings from Austria, Italy and South Korea,  some indications are presented  in Chapter 4.6 of the report 2016 R35«  Experience with significant incidents in road tunnels ».

An understanding of how smoke behaves during a tunnel fire is essential for every aspect of tunnel design and operation. This understanding will influence the type and sizing of the ventilation system to be installed, its operation in an emergency and the response procedures that will be developed to allow operators and emergency services to safely manage the incident. Detailed discussion on the topic can be found in Section III "Smoke behaviour" and Section 1 "Basic principles of smoke and heat progress at the beginning of a fire", which analyse in detail the influence of different parameters (traffic, fire size, ventilation conditions, tunnel geometry) in the development of an incident.

Some randomly selected examples of real tunnel fires (including a short discription and analysis of the event) can be found in Appendix 5 of the technical report 2016 R35 “Experience with Significant Incidents in Road tunnels"

Hazards due to DG-transport

Dangerous goods or hazardous materials are solids, liquids or gases that can harm people, other living organisms, property or the environment, considering their chemical or physical properties. A substance or a material presenting a particular hazard should be used, handled or transported taking into account the characteristics of that hazard. A substance or a material is considered dangerous when it:

• may cause damage to people who handle it,
• may cause damage to third parties and their property,
• may cause damage to the environment (atmosphere, soil, water, plants, animals, food chain);
• may endanger transport safety,
• may cause damage to the vehicle with which it is being transported.

A dangerous good can present more than one kind of hazard and therefore several risks. The different types of hazard that may occur during road transport are coded as:

• D-explosiveness,
• F-flammability,
• S-spontaneous combustion,
• SR-self reactive,
• W-water reactive,
• O-oxidizing,
• P-organic peroxide,
• T-toxicity,
• I-infectious,
• C-corrosivity.

The following table describes hazards posed by dangerous goods depending on their Class according to ADR classification.

Table 1: Hazards of Dangerous Goods classes

Class number	Class description	Hazard description
Class 1	Explosive substances or articles	• may cause undesired uncontrolled explosion, • may cause gas expansion and generate blast wave, • may cause property and physical damage, • launch of fragments at high speed and long distances.
Class 2	Gases	• they may be flammable, • they may be oxidising or at risk of oxidation, • in enclosed and closed rooms it can cause asphyxiation without being perceived, • they may be toxic, • if they are under pressure they may cause rupture (with possible explosion of the container), • if they are refrigerated (cryogenic) they can endanger human tissues, or if the temperature of the container  increases rapidly the pressure may cause an explosion; these gases may also be flammable.
Class 3	Flammable liquids	• cause of fire.
Class 4.1	Flammable solids, self-reactive substances, polymerizing substances and solid desensitized explosives	• flammability, • fire transmission, • smoke, • injuries, • damages.
Class 4.2	Substances liable to spontaneous combustion	hazards of substances and articles of this Class are due to the possibility of their automatic ignition on contact with the air and without cause (spark or flame); on contact with oxygen they may self-ignite.
Class 4.3	Substances which, in contact with water, emit flammable gases	• creation of flammable gases, • self ignition – fire.
Class 5.1	Oxidizing substances	• ignition, • fire – smoke.
Class 5.2	Organic peroxides	• easy ignition, • easy blast, • violent burning.
Class 6.1	Toxic substances	• danger to human health, • cause death when enter the body from the mouth, skin and nose within a few hours or days depending on the dose, • high toxicity.
Class 6.2	Infectious substances	substances are hazardous because they contain micro-organisms (bacteria, parasites, viruses) that can cause infections in humans and animals; they may also contain bacteria, parasitic organisms or viruses without antidote in case of infection.
Class 7	Radioactive material	Hazards arising from the transport of contaminated radioactive substances externally can cause: environmental damage, skin contamination, other environmental and animal dangers that may occur even after a long period of time. Radiation can affect humans externally or internally: externally when the source is outside our body, internally, when the body is exposed to radioactive material through inhalation, dust absorption, skin or eye damage and ingestion.
Class 8	Corrosive substances	• damage to the skin, eyes, mucous membranes and tissue necrosis, • corrosion, burning of other materials.
Class 9	Miscellaneous dangerous substances and articles	• hazard to health if they enter the respiratory system (asbestos) • source of poisonous gases in case of fire

 

Security aspects

In the context of road infrastructure, in particular road tunnels, security is understood as the preparedness, prevention and preservation of a road infrastructure against exceptional man-made hazards. This definition of security is complementary to that of safety, which is defined as the protection of road infrastructure against unintentional events such as accidents and is covered by relevant standards. Thus, the key distinction between security and safety is that:

• safety deals with events covered by relevant standards, while security focuses on exceptional man-made hazards (low-frequency, high-consequence events);
• safety deals with unintentional hazards (man-made and natural), while security additionally includes intentional events (man-made).

Security-relevant hazards which may affect road tunnel infrastructure, operations and users are e.g. terrorism, cyber-crime, theft or hoaxes.

In order to analyse the security level of an infrastructure and to decide about the implementation of protective measures, a security assessment should be conducted. The security assessment consists of a hazard and scenario analysis, a determination of the vulnerability of the asset and its important components (object level) and finally the consideration of the tunnel’s criticality (network level), meaning its importance for the road network as well as any interdependencies with other transport infrastructure and other sectors. In order to prioritize tunnels to be strengthened by protective measures, the criticality of the asset is the key criterion. It is recommended to rank elements of infrastructure according to their criticality before deciding on budget allocation for protective measures.

Regarding protective measures which could be implemented in order to strengthen security, there is generally a large overlap with safety measures (the boundaries between safety and security are often not clear). This overlap can be used to strengthen both safety and security and could help to get the necessary funding for protective measures. The same is valid for already implemented measures in existing road tunnels: many existing structural and operational safety installations could be used to prevent or mitigate both safety and security related events (e.g. cameras (CCTV) or incident detection systems (IDS)). Generally it is recommended to include security principles from the conceptual and preliminary design phases for a new tunnel (“Security by design”). Retrofitting an existing infrastructure with security measures is often much more expensive. When considering protective measures for existing structures, low budget security solutions in particular or measures with synergies with safety should be implemented. Additionally so-called “soft measures” should be taken into account (e.g. organizational measures, staff training, etc.).

For more detailed information refer to the technical report 2015 R01 “Security of road infrastructure”. The report contains also useful references and links to existing international literature as well as procedures and tools for security assessment. Some useful examples for protective measures are also mentioned in this report. Other PIARC outputs related to security that could be relevant are for example:

1. Security and safety of road tunnels and other critical infrastructures (R/R 350),
2. Risks associated with natural disasters, climate change, man-made disasters and security threats (2013R12EN),
3. The establishment of a management program for business continuity at the ministère des Transports du Canada-Quebec (R/R 370).

Prevention

Prevention is a key approach in the effort to minimise the risk of collisions and other significant incidents in a tunnel and therefore crucial for the development of a safe tunnel system. The preventive measures are those acting ahead of a dangerous scenario to reduce the probability of occurrence of situations which can have a negative impact on the safety of tunnel users.

Preventive measures are developed using activities and practices aimed at anticipating, avoiding, and removing possible causes of a hazardous event.

Safety measures in general are based on a systematic consideration of all aspects of the tunnel system, i.e. infrastructure, operation, users and vehicles. Each tunnel provides its own unique safety challenges, based on where it is located, its layout, length and cross section, as well as traffic volumes and patterns; therefore the safety measures have to fit the tunnel system.

In the specific confined environment of the tunnel, fire and the release of dangerous substances are the most critical incidents that are considered in relation to the catastrophic consequences that they can generate. For this reason, many safety objectives are closely connected to these phenomena.

Fire in a tunnel can be the consequence of a collision, or be triggered by different other causes such as overheating of the engine in traffic congestion or on long stretches of a climb, overheating of the braking system of heavy vehicles over long downhill sections, or shorting of electrical circuits.

If vehicle maintenance is outside the responsibility of a tunnel operator (which is typical), several technical measures can be implemented to avoid collisions in a tunnel.

First of all, a safe road design is fundamental to minimizing collision risk but of course it cannot be implemented as an additional preventive measure in existing tunnels. In any case, creating (and maintaining) an environment for drivers that enables them to assess the traffic situation and the course of the road and to anticipate the necessary actions they need to take as part of their driving task is fundamental to minimizing collision risk.

For tunnels in general, the relevance of tunnel lighting and adequate road signage are highly ranked. The quality of tunnel lighting assures better visibility, higher illumination density, a calming effect and in long tunnels it can be used to break monotony and keep the user focused. Moreover, a good quality lighting system should reduce or avoid the so called “black hole effect” when the eyesight of a driver entering a tunnel has to adapt to the changing light that can limit the sight distance or can cause drivers to slow down. Also optical lane guidance aids, such as reflectors or LED marker lights on the tunnel wall can help users to correctly perceive the road profile. The ventilation system plays an important role too in assuring the air quality and consequently good visibility inside the tunnel.

Dynamic warning signs (activated by detection) are likewise important to inform and alert users about dangerous situations (e.g. presence of an object on the road, stopped vehicles, closed lanes, difficult environmental conditions at tunnel portals), to reduce their speed, increase their level of attention and to avoid risky behaviour or to close the tunnel in order to avoid congestion occurring in the tunnel. From this point of view, all monitoring systems (sensors, video surveillance etc.) can contribute to minimizing the occurrence of critical situations.

An electronic overhead signal system is essential for lane control (such as lane closures) and to guide traffic away from closed lanes ahead.

Speed differences between vehicles is another common cause of collisions. Therefore an overtaking prohibition for heavy goods vehicles or the implementation of speed limits and speed control can be efficient measures especially when the viewing distance is limited. Furthermore, to prevent rear-end collisions ( a quite frequent collision type), it might be useful to control and enforce an adequate distance between vehicles driving in the same direction.

An effective preventive measure is constituted by preventive maintenance, above all for safety-related systems which are not redundant. This includes regular inspections, tests and cleaning of tunnel walls to maintain adequate safe conditions during the whole lifetime of a tunnel.

More information on preventive measures for tunnel collisions is provided in the technical report 2019R03EN “Prevention and mitigation of tunnel related collisions”.

Mitigation

With respect to the functionality of safety measures, a clear distinction can be made between preventive measures, i.e. safety measures aimed at reducing critical situations, and mitigation (protective) measures, aimed at reducing the consequences in case of an evolving incident.

Mitigation measures are related to softening the mechanical impact (e.g. safety barriers designed to absorb energy to minimise the degree of impact to a vehicle and the vehicle occupants), avoiding secondary collisions (by for example closing one or more lanes or the tunnel) or reducing and controlling the consequences in case of a fire arising within a tunnel.

The issue of fire safety in road tunnels has gained high visibility in the past following a series of dramatic fires which led to human casualties, major structural damages, and lengthy disruptions to the transport system with significant impact on regional economies. In a context where aging tunnels must cope with changed traffic composition and volumes, and where ever-longer new tunnels are built in increasingly challenging urban or geological environments, effective mitigation of the fire risks and their far-reaching consequences is paramount.

After an incident has occurred, the consequences must be faced with effective protection measures so that the users involved can save themselves and, at the same time, all those not directly involved can immediately react to avoid injuries and further damage.

Detection devices provide early warning of traffic incidents or abnormal conditions in the tunnel, which can result in the interruption of normal traffic flow. Verification devices and/or traffic management methods allow tunnel operators to rapidly confirm an incident and implement incident response scenarios to systematically close lanes or redirect traffic to prevent secondary collisions, and in the event of a fire, implement safe and efficient evacuation of users by means of information and communication. Furthermore, automatic fire-fighting devices like fixed fire-fighting systems can significantly reduce the consequences of a fire within a tunnel by controlling the fire development until the intervention of emergency teams.

A number of factors distinguish a tunnel fire from a fire in a conventional building. The escape environment for people is difficult in a tunnel, due to long escape distances and time, the potential for high fire loads and rapidly growing fires with intense smoke production filling up the whole tunnel section, combined with a rapid smoke spread. Tunnel fires may also cause extremely high temperatures, which can not only lead to structural spalling and even collapse, but can also make fire-fighting efforts more dangerous and time-consuming.

Fire prevention is of course the first priority, but it is essential to also integrate appropriate fire detection and response systems that will slow down structural degradation, ensure the safe evacuation of people, prevent fire spread, and facilitate fire-fighting efforts.

In a tunnel, detecting an incident a few seconds earlier can save lives and considerably reduce infrastructure damage and loss. Identifying a developing fire at an early stage (e.g. by video detection, smoke detection systems, linear heat detection systems, etc.) is a significant success factor in effective incident mitigation in tunnels. Indeed, long-term closures of damaged tunnels following a fire have in the past caused long-term economic consequences and extensive impact on other parts of the transport network. The implementation of appropriate fire mitigation measures can therefore be vital even from a merely economical point of view.

Other than the geometric design of a tunnel (length, section, emergency exit spacing etc.), the most important measures for the mitigation of the effects of fires have been demonstrated to comprise a permanent supervision by a control centre, the ventilation system, the monitoring system, the equipment used to close the tunnel and the fire resistance of equipment. In particular, adequate ventilation strategies are fundamental and they need to be correctly defined in order to be able to manage smoke control in different possible situations.

Immediately informing the control centre in the first phase of fire development and following appropriate actions and instructions can prevent worse situations. In this way it is possible to speed up both the evacuation process according to the information the control centre can provide to users and the intervention of the emergency services, contributing to the mitigation of the effects of collisions and fires.

More information on preventive measures for tunnel collisions is provided in the technical report 2019R03EN “Prevention and mitigation of tunnel related collisions”.

Self-Rescue

Self-rescue describes the ability of people involved in a tunnel incident to get away from a source of hazard by their own initiative and appropriate behaviour.  Experience from past tunnel fire incidents shows that smoke is the main problem for human safety in a tunnel fire. The opportunity to quickly reach a safe zone, which is not affected by smoke, is essential for mitigating the consequences of the incident. Hence the self-rescue principle is a key pillar of tunnel safety in case of a tunnel fire.

Fire in a modern building will normally give those in the building a reasonable opportunity to escape to a safe zone closely located from the area affected by the fire. In a tunnel, users have to escape to one of the portals to get outside of the tunnel. For long single-tube road tunnels without emergency exits to an escape route independent from the affected tunnel tube, a safe zone may be several kilometres away - often an unreasonable prerequisite for safeguarding the principle of self-rescue. Therefore modern tunnel guidelines include prescriptions for a maximum admissible distance of emergency exits leading to a safe zone, which can be an escape tunnel, an escape shaft, an exit to the open air or a parallel second tunnel tube. For instance, Annex I of the European Directive on minimum safety requirements defines a maximum admissible distance of 500m and national guidelines often define stricter requirements.

Serious incidents that challenge the self-rescue principle are fast-developing vehicle fires involving vehicles with a high fire load (mainly HGVs with combustible loads) which are able to produce a lot of smoke within a short period of time. However, a fire in a small vehicle can also turn into a larger fire, e.g. by involving several vehicles.

In any case, it is important to evacuate early and fast. Therefore, in addition to providing an emergency route to a safe place, measures are required to make sure people react quickly and evacuate early through the emergency exits.

A closer look into the self-rescue process reveals that the evacuation behavior of people can be divided into several phases. At the beginning is the pre-evacuation phase, which includes all events before the start of the evacuation and ends with the decision to escape. In the subsequent evacuation phase, we can distinguish the pre-movement phase and the movement phase. During the pre-movement phase, the tunnel user searches for information and selects an escape route. The movement phase includes all behavior that tunnel users display during the evacuation until they reach an escape target.

Hence, it is important to support this procedure by providing relevant information and giving clear instructions to people - visually or acoustically.

Further, self-rescue may be influenced by tunnel parameters and traffic conditions. For instance, there is a close link between self-rescue and smoke management strategies.

In tunnels with two tubes operating with unidirectional traffic and longitudinal ventilation, the ventilation typically supports smoke propagation in the driving direction (the initial direction of smoke propagation due to traffic-induced airflow). The smoke gradually affects the empty part of the tube in front of the incident. People that are stuck in traffic behind the incident can evacuate to the other tube and are normally not affected by the smoke. The second tube will normally be closed to traffic, and can be considered a safe zone to evacuate to. There is also a safe evacuation passage between the tubes.  In unidirectional tunnels with regular congestion or in bidirectional tunnels the situation is more complex, as vehicles are likely to be blocked on both sides of the fire site; hence the interaction between self-recue and the strategy of emergency ventilation gets more complicated. However, modern risk assessment tools are able to investigate this process in detail for particular situations, thus providing valuable information for optimizing the interaction between human behaviour, procedures and technical equipment.

Furthermore, a steep evacuation route may also affect the ability to perform self-rescue as well as smoke propagation behaviour. Therefore, tunnels with high gradients require special attention.

Public education is important in providing knowledge and skills for self-rescue initiatives to road tunnel users.  Information campaigns and publicity provided by road tunnel operators or authorities can help road-tunnel users understand the self-rescue measures to adopt when they encounter an emergency. In the context of self-rescue, special issues regarding people with reduced mobility have to be taken into account - see technical report 2008R17 “Human factors and road tunnel safety regarding users “

Many of these topics are also discussed in Section I "Objectives of fire and smoke control" of report 05.05.B, which includes a detailed discussion on tenability criteria under fire situations.

Emergency response

Emergency response measures are a group of measures covering the reaction of the tunnel operator, the emergency services and other organisations to a significant tunnel incident requiring intervention beyond normal operational procedures. As there is a wide range of different incidents, the measures required are diverse. For instance, a simple breakdown of a vehicle in a traffic lane might require the closure of this lane or of the whole tunnel tube. This example demonstrates the complexity of the topic “Safety measures”, because this response measure to the “breakdown” incident would also be considered to be a preventive measure against collisions.

Emergency response measures are typically complex because they interact with safety procedures and tunnel safety equipment as well as with human behaviour involving tunnel users, tunnel operators and emergency organisations. Among the possible hazards to be considered in road tunnels, vehicle fires are a particular concern because they can occur quite often, and the consequences can be more severe in a confined space. Therefore it is a fundamental requirement for every tunnel to make rescue and firefighting operations possible, even if the conditions might be quite different from case to case.

Whereas the operators know their tunnels quite well, firefighters need to perform tactically demanding work in a more or less unknown situation, compared with the daily challenges in industry and buildings. It is crucial for safe outcomes that firefighters have basic training in tactical methods for collecting information, search and rescue, and firefighting in tunnels.

Incident command needs knowledge about tunnels and tunnel fires in general and the specific characteristics of an individual tunnel in particular, and also knowledge about tactical dispositions of crews. Incident command needs to make the decisions in a very demanding situation, in terms of information access, efficient cooperation with the tunnel operator and interaction with a complex environment of tunnel infrastructure and technical safety systems. In order to cope with these challenges, it is important to establish close working ties between tunnel operators and local firefighting organisations in order to share knowledge on the specific tunnels, and to keep the fire-fighters updated on any aspects relevant for safety, such as changes in equipment, operational procedures, traffic conditions etc.

It is also important to carry out assessment of preparedness, contingency planning and regular training for each tunnel. For these reasons, several PIARC reports treat the issue of fire safety and emergency response in road tunnels.

Part of the material included in these reports relates to specific tunnel features and is dealt with in the corresponding chapters of this manual, for instance:

• incident detection in chapter Monitoring / Incident detection
• strategies for emergency ventilation in page Ventilation strategies and report 2011R02 ,
• technical systems for mitigation of fire hazards in chapter Mitigation of fire hazards
• specific measures for emergency services in chapter Emergency services response 

Some tunnels are a crucial part of the traffic infrastructure in a region or a city. If their availability is impaired this might have a major impact on the mobility of a whole area. For such tunnels it is important to assess the consequences of major incidents  - accidental or intentional - on tunnel structure and equipment as well as the risk of resulting long-term tunnel closures and consider counter measures that can minimise closure time after a tunnel fire. The emergency response capabilities are often a crucial part of protecting the infrastructure, but other active and passive protection measures should also be considered.

Specific measures for DG-transport

A joint OECD/PIARC research project (ERS2 project: 1997-2001) led to an investigation of measures that could reduce the probability and/or consequences of an incident involving dangerous goods in a tunnel, where such goods are allowed.

Possible measures were identified and in a  second step an attempt was made at evaluating the cost-effectiveness of these measures with respect to dangerous goods hazards. The focus was put on the effectiveness of measures as costs are specific to a particular tunnel project and cannot be assessed at a general level.

Some of the possible risk reduction measures are directly taken into account in the Dangerous Goods Quantitative Risk Assessment Model (DG QRAM) developed under the project . The effectiveness of each of these measures, or each combination of measures, can be assessed by running the model with and without the measure(s) and comparing the results. A large number of tests were undertaken, and this showed that no general conclusion could be drawn regarding the effectiveness of measures because the effectiveness very much depends on the specific case. An assessment of effectiveness should thus be made on a project basis.

The effectiveness of other measures (which are not directly included in the DG-QRAM model) was much more difficult to assess and methods were proposed to take a number of them into account. More information can be found in chapter VII of the OECD project report (Risk reduction measures).

Safety procedures & organisational aspects

Safety procedures are meant to explain how the operational staff should apply safety measures.  

A first general level should:

• Identify measures to be applied continuously (for example surveillance of the tunnel) and measures to be applied in certain circumstances. For instance, in case of an incident  these are generally mitigation measures, or measures to support self-rescue or emergency response actions. The incident may be traffic-related (breakdown, collision, or fire for instance) or involve staff or tunnel equipment.
• Identify and describe the relevant circumstances in which a given measure should be applied
• For each circumstance
  
  • List and prioritize the measures that should be applied and the timeline
  • Indicate the main purposes of each measure
  • Identify who is responsible for applying each measure
  • If there is more than one person involved in the decision process leading to the application of the measure:
    • Identify the decision process
    • Identify the persons involved

A more precise level explains in more detail how each measure is to be applied:

• Description of the subtasks to be done to apply the measure, including equipment to be used
• Identify the staff or stakeholders involved and/or impacted by the application of the measure

These safety procedures should be concise and clear, so that the persons involved in applying a safety measure have no doubt about the required actions and can act efficiently.

Risk assessment

In addition to the traditional prescriptive approach, a risk-based approach - called risk assessment - can be used to address the specific safety features of a tunnel system (including vehicles, users, operation, safety systems, infrastructure conditions, and emergency response) and their impact on safety.

Various types of risk can be addressed in a risk based approach, such as harm to a specific group of people (societal risk), or to an individual person (individual risk), loss of property, damage to the environment or to immaterial values. Commonly, risk analyses for road tunnels focus on the societal risk of tunnel users which can be expressed as the expected number of fatalities per year or as a curve in the FN diagram showing the relationship between frequency and consequences (in terms of number of fatalities) of possible tunnel incidents.

Risk assessment is a systematic approach to analyse sequences and interrelations in potential incidents, thereby identifying weak points in the system and recognising possible improvement measures. Three steps characterise the risk assessment process:

• Risk analysis: Risk analysis is concerned with the fundamental question: "What might happen and what are the probabilities and consequences?". It involves the identification of hazards and the estimation of the probability and consequences of each hazard. Risk analysis can be carried out in a qualitative or in a quantitative way or as a combination of both. Two families of approaches are suitable for road tunnels:
      - a scenario-based approach, which analyses a defined set of relevant scenarios, with a separate analysis for each one,
      - a system-based approach, which investigates an overall system in an integrated process, including all relevant scenarios influencing the risk of the tunnel, thus producing risk indicators for the whole system.
  For system-based risk analyses, quantitative methods are common practice. Thus probabilities of incidents and their consequences for different damage indicators (e.g. in terms of fatalities, injuries, property damage, interruption of services) and the resulting risk are estimated quantitatively, taking due account of the relevant factors of the system and their interaction.
• Risk evaluation: Risk evaluation is directed towards the question of acceptability and the explicit discussion of safety criteria. In other words risk evaluation has to give an answer to the question "Is the estimated risk acceptable?" For a systematic risk evaluation safety criteria have to be defined and determination made of whether a given risk level is acceptable or not. Acceptance criteria must be chosen in accordance with the type of risk analysis performed. For instance, scenario-related criteria can be set to evaluate the results of a scenario-based risk analysis, while criteria expressed in terms of individual risk (e.g. probability of death per year for a specific person exposed to a risk) or societal risk (e.g. reference line in a FN diagram) can be applied for a system-based risk analysis. There are different methods of risk evaluation: it can be done by relative comparison, by a cost-effectiveness approach or by applying absolute risk criteria. However, in practice a combination of different approaches is often applied. Important principles for risk evaluation as well as practically applicable risk evaluation strategies are presented in the technical report 2012 R23 “Risk evaluation, current practice for risk evaluation for road tunnels”.
• Planning of safety measures: If the estimated risk is considered as not acceptable, additional safety measures have to be proposed. The effectiveness (and also cost-effectiveness) of the additional measures can be determined by using risk analysis to investigate the impact on the frequency or consequences of different scenarios. Planning of safety has to answer the question "Which measures are best suited to get a safe (and cost-efficient) system?

The simplified flowchart in Figure 1 illustrates the main steps of the risk assessment process

Risk assessment of road tunnels allows a structured, harmonised and transparent assessment of risks for a specific tunnel including the consideration of the relevant influencing factors and their interactions. Risk assessment models provide a much better understanding of risk-related processes than merely experience-based concepts may ever achieve. Moreover, they allow evaluation of the best additional safety measures in terms of risk mitigation and enable a comparison of different alternatives. Hence, the risk assessment approach in the context of tunnel safety management can be an appropriate supplement to the implementation of the prescriptive requirements of standards and guidelines. In practice, there are different methods to approach different kinds of problems. It is recommended to select the best method available for a specific problem.

Although risk models try to be as close to reality as possible and try to implement realistic base data, it is important to consider that the models can never predict real events and that there is a degree of uncertainty and fuzziness in the results. Considering this uncertainty, the results of quantitative risk analysis should be considered accurate only to an order of magnitude and should be supported by sensitivity studies or similar. Risk evaluation by relative comparison (e.g. of an existing state to a reference state of a tunnel) may improve the robustness of conclusions drawn but care should be taken in the definition of the reference tunnel.

Risk assessment for DG transport

Banning dangerous goods from a tunnel does not eliminate the risks, but modifies them and moves them to a different location, where the overall risk may actually be greater (diverting through a dense urban area for instance). For this reason, a joint OECD/PIARC research project recommended that decisions on authorisation/restriction of dangerous goods in a tunnel should be based on a comparison of various alternatives and should take into account the tunnel route as well as possible alternative routes.

A rational decision process was proposed, with the structure shown in the figure below. The first steps would produce objective risk indicators, based on quantitative risk analysis (QRA). The last steps would take into account economic and other data, as well as the political preferences of the decision maker (risk aversion for instance). These later steps could be based on a decision support model (DSM).

 

The OECD/PIARC project has developed a risk model as well as a DSM. The DG QRAM model is currently used in a number of countries. It is a system-based risk analysis model and produces indicators of the societal risk (F-N curves for the tunnel users and for the permanent neighbouring population), as well as the individual risk (for people permanently living in the neighbourhood of the tunnel) and damage to the tunnel and the environment. It is applicable both to routes including tunnels and to open-air routes, so that the risks on various alternative routes can be compared. The model is based on 13 scenarios representative of each of the five tunnel categories (although categories D and E cannot be distinguished because they lead to similar risks).

This model is currently being updated by PIARC in two steps, in order to adapt it to a modern hard and software environment and to enhance its abilities based on the comprehensive application experience available. It can be bought from PIARC and is described in more detail on its website. However, it has to be stressed that the procedures and algorithms of DG-QRAM were only developed for assessing risks due to dangerous goods. Hence, they are not appropriate to any other types of risk analysis.

In the course of the implementation of the ADR tunnel regulations, various countries have developed specific risk evaluation procedures for the transport of dangerous goods through road tunnels, in order to optimize the benefit and minimize the expenditure for studies. Typically this is a multistage risk assessment process starting with a simple parameter check, followed by a study of the intrinsic DG tunnel risk and ending with an investigation of alternative transport routes. The risk assessment study can be based on DG-QRAM, but in some countries, for instance in Germany, for some steps other methods are also used (for more information see technical report 2012R23 « Current practice for risk evaluation for road tunnels », appendix 2)

Additional information as well as examples of application can be found in the following PIARC references:

• "Quantitative Risk Assessment Model For Dangerous Goods Transport Through Road Tunnels" in Routes/Roads 329 (2006)
• Section 4.6 "OECD/PIARC Dangerous goods QRA model" of report 2008R02 and Annex 3.7 "OECD/PIARC DG QRA model" of report 2008R02. 

Improving safety in existing tunnels

• Why upgrade existing tunnels?
• Proposed methodology to assess and improve existing tunnels

Why upgradE existing tunnels?

As a consequence of the major disasters in road tunnels (Mont Blanc tunnel fire in 1999, Tauern tunnel fire in 1999 or Gotthard tunnel fire in 2001), specific attention was turned to the safety standards of existing tunnels. Existing tunnels require specific approaches and tools to identify and evaluate the need for safety upgrade programmes. Substantial research and studies followed these major tunnel fire incidents, demonstrating that many existing road tunnels require additional and specific means to ensure a safe environment for users. Even where previous improvement programmes have been carried out, existing tunnels may not be in line with the current safety standards because of upgrading of regulations in the meantime.

These incidents and subsequent studies have raised awareness of tunnel risks amongst individuals involved in road tunnels, from designers and operators to authorities' representatives. It has become clear that safety upgrading is not only a matter of improving the structure and/or equipment, but that there is also, and sometimes mainly, a strong need to clarify the organisation of safety management and to adapt associated procedures.

In the assessment of safety in existing tunnels, special attention should be paid to changes in the tunnel environment (traffic volume and composition, dangerous goods transport, construction works in the surrounding area, etc) which may also induce the requirement for upgrading measures.

Proposed methodology to assess and improve existing tunnels

A structured approach for assessing and preparing refurbishment programmes is proposed with two main tasks:

• The first task aims to assess the current situation of the tunnel, like an instantaneous picture of the tunnel, in order to identify the current safety level. First of all a reference safety level must be defined, which is generally provided by regulatory frameworks. Then the current tunnel functionalities and the state of the facilities which perform them have to be analysed. On this basis, it must be assessed whether the existing tunnel is currently in line with safety-relevant design criteria. Furthermore, specific risks should be assessed by risk analysis which is an appropriate tool to evaluate the current safety level of a tunnel in operation. From these initial analyses, actions can be defined and priorities can be set
• The second task aims to define the future tunnel situation after renovation works which can be acceptable in relation to the defined safety level goal. This can be done by developing renovation programmes and again assessing the safety level of the renovated tunnel, including all upgrading measures. Once again risk analysis can be applied to demonstrate an adequate safety level or to evaluate various alternatives of upgrading measures, including cost-effectiveness criteria. Renovation programmes depend on the specific context of each tunnel, its constraints and its environment. An iterative risk analysis process may be followed where agreement is reached on a projected safety level that is acceptable to all stakeholders in the project.

The multistage process for the preparation of a tailor-made renovation programme for a tunnel in operation can be summarised in the flowchart below. It describes the functional links between the various steps and their respective outputs.

In detail, the content of each step is to be adapted to the specific conditions of the individual tunnel, its environment, and of course specific local practice.

Depending on the tunnel situation, the process can be stopped after step 3 with a simple comparison to the reference state if the analysis is demonstrating that the required safety level is already achieved. Indeed, for tunnels already renovated, step 3 can be the end of the process. If not, step 3 may highlight urgent mitigation measures which can be implemented immediately to improve the tunnel safety level with non-substantial actions such as closure barriers, signalling or traffic control measures. In some cases, such measures may be sufficient to obtain the required safety level.

If more substantial works are required, temporary modifications of the operating conditions may be a useful tool for a temporary increase in the tunnel safety level, if necessary.

The preparation of renovation works for a tunnel in operation is an iterative process, as it is a combination of technical issues, safety measures, cost implications and works phasing constraints. This is why step 4 and 5 can be refined several times to obtain an adapted refurbishment programme taking into account all relevant parameters which may influence the decision. Design activities can start after step 5.

Report 2012R20 "Assessing and improving Safety in Existing Road Tunnels" provides guidelines for each step within this process, up to the definition of an improvement programme.

Typical weak points (safety deficiencies) in existing tunnels are presented in Appendix A of this report. Additionally, case studies of existing tunnels in Europe demonstrate the strategy adopted for renovation works and upgrading measures implemented (Appendix B).

Collection, ANALYSIS and evaluation of tunnel incident data

Collection and analysis of incident data, as detailed in Chapter 3 "Collection and Analysis of Data on Road Tunnel Incidents" of report 2009R08 are essential for the risk assessment of a tunnel and for the improvement of its safety measures. The process is two-fold, starting at the local tunnel level to cover specific needs, like input data for risk analysis, and extending to fulfil legal obligations such as reporting statistics at national/international level. The evaluation of specific events (accidents and incidents) may help to identify specific hazards in a tunnel as well as to optimise operational procedures and the reaction of safety systems. As well as analysis for real incidents, analysis of data from safety exercises can help to gain experience in the management of incidents under realistic circumstances.

Practical issues of incident data collection are further addressed in Chapter 2 of the report 2016R35 “Experience with Significant Incidents in Road Tunnels”, based on the 3 fundamental steps of the incident data collection chain, which are collection, correction and  interpretation (see figure 1).  Practical problems and limitations are discussed and recommendations for improvements are given.

In particular, it has been noted that it can be very time-consuming to collect all necessary data for a relevant evaluation leading to improved safety procedures or for incident statistics used in risk analysis. There can be a conflict in available and required resources for data collection. It is therefore recommended to clearly define the data collection chain and identify all parties involved. All stakeholders should define their feedback objectives, whilst taking into account the difficulties to obtain and correct data and the resources needed. Based on the objectives and available resources, the required data should be clearly identified, as well as in which time period the data should be collected (immediately after/during the incident or at a later stage) and which parties should be involved in the data collection. In order that the parties involved remain motivated, two main actions have to be handled. First of all, the purpose of data collection has to be made clear. Secondly, lessons learned and benefits such as improved procedures and systems have to be provided.

Safety inspections

Safety inspections, as explained in Chapter 4 of the technical Report 2009R08 (Safety Inspections of Road Tunnels) are a tool to assess the current tunnel safety level either within a legal framework (European Directive for instance) or against an accepted level of risk. PIARC has developed an organisational scheme based on the EU Directive 2004/54/EC to describe the chain of safety responsibility concerning safety inspections and clarify the responsibilities of the involved parties. It also proposes the contents of a safety inspection (infrastructure and systems, safety documentation and existing procedures, tunnel management organisation, training and quality assurance) along with a comprehensive roadmap with all the necessary steps and preparation needed to carry out a safety inspection.

A road is a linear traffic infrastructure which is generally located in open terrain and sometimes in a closed environment like tunnels. It is important to have a uniform approach to road safety management outside and inside tunnels. For tunnels, it is necessary to take additional considerations into account which requires expert opinion from tunnel safety/tunnel operation experts, including information from the tunnel operator, the tunnel manager and the Traffic Control Centre. Safety inspections in tunnels often require a more complex evaluation than on open roads.

Transition areas between tunnels and open roads are of particular interest in terms of their impact on road safety. Diversions, as a result of entire or partial tunnel closure due to maintenance works or incidents in the tunnel, are situations that can often have an increased risk. Hence, it is just as important to evaluate such exceptional situations as the regular tunnel operation.

Safety documentation

Safety documentation is the safety record of a tunnel throughout its whole lifetime, containing a survey of all safety-relevant information; it should therefore be compiled for each tunnel beginning with the design stage. The demands for this information are different depending on which stage the tunnel is at in its life-cycle: design, commissioning, or operation.

At the design stage, the safety documentation focuses on the description of tunnel infrastructure and traffic forecasts, whereas at the operation stage the operational aspects, such as emergency response plans and measures for transportation of dangerous goods, gain importance. The degree of detail in the information increases as the project develops.

The safety documentation should comprise 'living' documents which are continuously developed and updated. It should include details of changes to tunnel infrastructure, traffic data, etc, as well as important findings from operational experience (i.e. analysis of significant incidents, safety exercises, etc.). More information is available on Chapter 2 "Road Tunnel Safety Documentation" of report 2009R08.

Emergency exercises

For road tunnels, emergency exercises should be regarded as an integral part of the tunnel emergency planning process. These exercises provide road tunnel operators with a very good opportunity to test operational instructions and highlight good practices and deficiencies, thereby helping all participants to be prepared for real events. Thus, evaluation and reporting are also essential components of emergency exercises.

In many countries, road tunnel safety regulations specify the time intervals between emergency exercises and sometimes give some indication about the contents of the exercises.

For tunnel operators, organising such emergency exercises represents a considerable task. It is notably very important for road tunnel operators to clearly define the objective(s) of each exercise and to adapt its scenario accordingly.

Technical report 2012R25EN "Best practice for road tunnel emergency exercises", inspired by a survey of current international experience in this field of expertise, provides a step-by-step guide on how to define the objectives, prepare, carry out and assess an exercise in the most efficient way. It also includes practical information on the resources required, the costs and the results to be achieved.

The report is useful as a checklist to help emergency exercise planning officers to:

• establish exercise objectives
• choose the most appropriate type of exercise to meet those objectives
• establish the human and technical resources needed
• control an exercise
• conduct a post exercise analysis
• evaluate the result of the exercise.

Technical report 2008R03 "Management of the operator-emergency teams interface in road tunnels" further elaborates on emergency exercises. The report highlights the necessity for contingency planning, for tunnel familiarization, for periodical exercises and for post incident analysis.

Making exercises as realistic as possible is commonly emphasized in post-accident analyses of incidents or fires and debrief reviews of emergency exercises. It is also important to ensure that emergency exercises remain acceptable in terms of staff safety, in terms of inconvenience to tunnel users and in terms of impacts on equipment.

Lessons learned from several major incidents have shown the necessity to form a partnership between the operators and the emergency services.  Both parties can be familiarised with practices through visits and emergency exercises.

Exercises where operators and emergency services train together may include:

• table-top exercises without using operational processes that put people on alert. Such exercises test communication, or provide staff exercises, or consist of written exercises simulating the operational activation and control procedures
• partial exercises that employ limited materials and personnel so as to test a precise part of the contingency planning for rescue
• full-scale exercises, that activate and control the whole of the contingency planning for a serious event such as a lorry fire, or an incident with numerous casualties, etc.

Table top exercises are very useful for all emergency response services. This kind of exercise is of great value from a cost-benefit point of view to all parties involved in tunnel safety. It can successfully be conducted throughout the whole chain of response, from the operation centres, through the commanders and to the operative intervention personnel. Exercises using computer based simulator programs are regarded as both useful and effective, and enable the personnel to exercise in a virtual reality mode.

From time to time, the operator and emergency services need to organise joint rescue exercises with the participation of all possible emergency response services such as the traffic police, the operator or the owner of the tunnel, the medical services and the emergency services. Joint rescue exercises help all parties involved in a tunnel incident to understand each other’s responsibility as well as the expectations that rest upon the different parties during an operation that aims to save lives and or to minimize damage to a tunnel, the installations or to the environment. The results of each such exercise should be analysed. If lessons drawn from an exercise reveal any deficiencies, the intervention strategies should be reviewed.

Training of emergency services

Emergency services liable to be called on to intervene in road tunnels obviously need to have the general training required to help people and combat fires in any type of infrastructure. Tunnels are confined spaces in which a crisis or fire can very quickly render rescue operation conditions more complicated. Over and above their technical skills, fire fighters therefore need to be trained specifically for this type of intervention. This training must develop their behavioural knowhow and enable them to deal appropriately with the complex situations they may be confronted with in a tunnel. This knowhow is particularly crucial for the supervisory staff who must be capable under all circumstances of adapting the operational methods initially envisaged, if needed. In order to fulfil this mission, good coordination with the tunnel staff is decisive, requiring meticulous preparation, follow-up and implementation of intervention plans, emergency exercises, and training based on feedback from actual experience.

In the case of cross-border tunnels, attention needs to be drawn to the collaboration required between the countries concerned in order to ensure effective coordination between the rescue teams in crisis situations.

With respect to the rescue teams, the following aspects are emphasized in technical report 2008R03 "Management of the operator-emergency teams interface in road tunnels":

• the most relevant lessons learnt from the most serious tunnel fires of the last decades (Chapter 1 "Lessons learned" of report 2008R03)
• information and recommendations for best practice. These are based on experience and lessons learnt (Chapter 2 "Detailed recommendations" of report 2008R03).

Emergency services are advised to exercise regularly so as to be able to face any situation that may occur in road tunnels. Exercises should always be according to pre-planned operations based on local risk analysis and risk assessment. In addition to these formal exercises, experience shows that it is very important for emergency teams to regularly organise technical visits of the tunnel, its equipment and safety facilities.

Technical report 2007R4 "Guide for organizing, recruiting and training road tunnel operating staff", gives information on the general principles for the training planned for a first response team. This training should include the following aspects in total or in part:

• internal organization and procedures including the knowledge of the services and professions present in the operating structure, methods of working, record-keeping procedures, reports, etc.
• knowledge of the layout of the tunnel and associated infrastructure
• knowledge of all access means to the tunnel (including escape means)
• knowledge of the location of all the technical rooms of the structure (e.g. control cabinets for fire safety systems or ventilation).
• knowledge of the location and use of all the safety facilities within the structure
• available means and possibilities of intervention from the control centre (communication means with the operator and their mode of use)
• use of special incident response equipment