Operational tasks

Generally speaking, tunnels are considered to provide a suitable or even higher level of safety the the open road network, Nevertheless, the potential consequences of incidents (breakdown, accident or fire) may be far more serious in tunnels than in the open air. Moreover, as tunnels are very often obligatory crossing points and are sometimes bottlenecks on the network, each total or partial closure can lead to major traffic disruptions or can oblige users to travel long distances on alternative routes.

For these reasons, operators and road authorities have to ensure the operational continuity and safety of road tunnels. They must guarantee to the users crossing the tunnel a level of service quality and safety complying strictly with regulatory requirements in force.

Depending on national regulations, tunnel operators and/or traffic police have to manage the traffic in tunnels (and on the route where the tunnel is located). In particular, they need to cater for the safety of users and any staff who may be working inside the tunnel (operating staff, sub-contractors, etc.). In several countries, the traffic police are in overall charge of traffic management and traffic patrolling, while the operator is in charge of operational tasks such as maintenance, operation of tunnel equipment, traffic surveillance and traffic assistance.

Generally speaking, typical tasks for the operators are:

Traffic surveillance and operation of tunnel equipment
Major tunnels (in terms of length, traffic density and complexity of the tunnel) are usually managed from a Traffic Control Centre. Very often, the Control Centre is equipped with remote surveillance systems (e.g. closed circuit television, automatic incident detection) and can remotely control certain equipment (ventilation, signalling, tunnel closure barriers, etc.).

Traffic Patrols
In certain cases, the operator can also deploy patrols that can provide a direct surveillance of tunnel users. These patrols can intervene very rapidly in case of need.

Management of civil engineering works
Civil engineering works in the tunnel undergo regular inspections. There is also regular maintenance of facilities such as drainage systems, gutters and all secondary structures (premises inside the tunnel, technical rooms, etc.),

Management of equipment
In major tunnels, the operator deploys several types of equipment that in the operation phase are under its own control. Tunnels are also equipped with systems that allow the operator to monitor the status of equipment. The operator must cater for the maintenance of equipment fitted in the tunnel. Here again, it is possible to have access to computerised tools to assist in performing this task.

Management of emergency situations
Whatever the nature of the  incident, whether it is a problem related to traffic (accident, interlinked accidents, fire, etc.) or to equipment (loss of power supply, malfunctioning of data transmission network, etc.), to intervene or to inform/activate the pertinent service/authority is the standard duty of the operator in charge of the surveillance.

Technical and Administrative management  
In addition to tasks directly related to tunnel operation, the operator provides the technical and administrative services supporting the management of the infrastructure and, of course, the personnel. The operator caters for the design of any equipment upgrading, the direction of the works, the investment and operational budgets for the proper functioning of the tunnel. Lastly, the operator also develops statistics and monitors the achievement of its own objectives by preparing periodical reports on the operation of the tunnel/route (financial indicators, traffic indicators, etc.).

The Technical report 05.13.B "Good Practice for the Operation and Maintenance of Road Tunnels" deals with this subject in parts 2 and 4.

STAKEHOLDER co-operation

The management of road transport is a very complex task. It is even more complex within a tunnel environment. Part of this complexity is due to the fact that skills and competencies required for the management of tunnels are scattered among different services. The cooperation of the different stakeholders is clearly a vital pre-requisite for effective traffic and incident management. 

The main stakeholders that need to cooperate are:

• The tunnel operator;
• The operators of different parts of the road network who have to be notified in case of tunnel closure or traffic restrictions;
• National and local administrative authorities to whom reports have to be submitted as required under regulations;
• The tunnel owner (if this is not the same entity as the tunnel operator), who also has to be kept informed;
• Traffic police and fire and rescue services, with whom coordinated intervention plans have to be prepared so that they can intervene in an efficient manner in response to any type of incident;
• Other sub-contractors (cleaning, maintenance, breakdown services for users, etc.)

The Technical Report 2007R04 "Guide for organizing, recruiting and training road tunnel operating staff" defines the organisational tasks in a more precise manner.

Organisation of operations

Although the organisation of tunnel operations varies from one country to another, generally  it involves the following groups:

• Operating staff in charge of operation management and traffic assistance
• Technical staff in charge of the maintenance and management of the civil engineering works and equipment;
• Administrative personnel.

In a few cases, emergency rescue services are considered as part of the operating staff.

In some cases, a single organisation can be responsible for all the personnel required for tunnel operations. In other cases, operations may be shared by several public and private organisations. For example, the tunnel owner or the road administration may entrust a public or private organization with operation as a whole and then contract out specific operational tasks (e.g. maintenance tasks).

Incident management measures depend on national regulations and local requirements specific to each tunnel. Consequently, the organization of the operator and the traffic police depends on the local context.

Technical Report 2007R04 defines the organisation of operation in greater detail in chapter 4 "Operating staff: tasks and facilities".

Operation of complex underground tunnels

• 1. Traffic
• 2. Emergency evacuation - Emergency access
• 3. Ventilation
• 4. Communication with users
• 5. Interfaces and cooperation between stakeholders
• 6. Interfaces and cooperation between operators
• 7. Safety

The operation of complex tunnels and underground networks must take into account specific factors and in particular:

1. Traffic

The volume of traffic is generally a more significant factor and in high traffic volume conditions traffic congestion is much more frequent. It follows that the number of persons in the tunnel is much higher and in the event of an incident, the number of users to evacuate will be more significant. 

Ramp merge and diverge areas are important locations in terms of risk of accidents. 

The assumption, which is sometimes prevalent from the start of projects, that there will never be a traffic blockage must be analysed with much circumspection. It is indeed possible to regulate the volume of traffic entering into an underground network in order to eliminate all risk of bottlenecks. Nevertheless, this leads to a significant decrease in the capacity of the infrastructure (in terms of traffic volume) which often goes against the reasoning that justifies its construction. Over time, measures of reducing entering traffic must be relaxed, or even abandoned because of the need to increase traffic capacity.  The probability and recurrence of bottlenecks increase, disregarding the initial assumption upon which the network was based (particularly in terms of safety and ventilation during incidents).

2. Emergency evacuation - Emergency access  

Issues to take into account include:

• The potentially higher volume of road users needing to evacuate, and the consequent necessity of providing adequate information, communication and evacuation aids, 
• The complexity linked to the “network” and its numerous branches, the eventual multiplicity of operators and the resulting interfaces, the precise location of incidents and users to secure and evacuate,
• The delays in response times, taking into account the traffic and possible congestion of the surface network, a correct identification of the incident locations, and adequate definition of access points and incident engagement methods,
• The necessity of response teams to have a good knowledge of the network, leading to a reinforcement of training and practical sessions.

3. Ventilation  

Ventilation systems in complex tunnels and underground networks must take into account:

• The volume and classification of traffic, as well as its evolution over time,
• The traffic congestion risks, generally making the construction of a smoke extraction system essential, 
• Environmental constraints especially discharge points for polluted air, release methods and their acceptability. This may require:
  • The construction of discharge points that are remote from the main alignment and the construction of ventilation galleries independent of the tunnel for connecting the tunnel to the shafts, 
  • The implementation of in-tunnel air filtration systems before release into the atmosphere
• The multitude of network branches and the necessity of making them operationally independent of each other to prevent the spread of fumes throughout the network should there be a fire.

4. Communication with users  

Communication with tunnel users must be reinforced and adapted throughout the multitude of branches within the network. Communication must be able to be differentiated between the different branches according to operational needs, especially in the case of fires. 

Users must be able to identify their position inside the network, which would require, for example, the installation of specific signs, colour codes, etc. 

Directional signs and prior information signs at interchanges or ramps must be subjected to careful consideration, particularly the visibility distances with regard to signals and the clear legibility of the signage.

5. Interfaces and cooperation between stakeholders  

Attention must be given to the interfaces and cooperation between stakeholders, notably for traffic management matters and safety matters (especially fire incidents), including evacuation of users and intervention of emergency response agencies in response to fire incidents.

6. Interfaces and cooperation between operators  

A complex underground network is usually operated by numerous operators whose cultures, skills, objectives and organisations are multiple and often different. However, the safety conditions inside the network and the level of service provided to users require good coordination between all the operators, together with excellent mutual understanding and confidence.

A Coordination Committee with a strong leadership is therefore absolutely essential.

Control centres must take account of the interfaces within the network and between diverse operators. They must allow the transmission of common information which is essential to each operator, and facilitate the possible temporary hierarchy of one control centre over another. The architectural design of the network of control centres, and of their performance and methods, must be subjected to an overall analysis of organisations, responsibilities, challenges and risks.  This analysis should reflect a range of operational conditions such as during normal and emergency scenarios and should review the interaction between the different subsections of the network and the respective responsibilities of each control centre.   

7. Safety  

The safety conditions of a complex underground network do not differ fundamentally to those of a standard tunnel. However, everything is more complex, due to:

• the geometrical complexity of the network, its numerous branches and all the associated infrastructures,
• the multiplicity of the operators, their various cultures and experiences, as well as their perimeters of very diversified actions
• the multiplicity of the interfaces and the need for coordination and solidarity,
• specific intervention difficulties for the emergency teams, in particular regarding the location of the event (especially of a fire), feedback on the magnitude of the event and the situation of the users concerned, as well as the intervention strategies.

Excellent knowledge of the networks and the conditions faced within the network during an emergency are therefore absolutely essential. Certain tools may be helpful, such as:

• a 3D virtual model of the infrastructure and the facilities,
• a virtual model and simulator for good knowledge and understanding of ventilation performance and operation, its aeraulic efficiency and the actual behaviour of the network.
• comprehensive contingency emergency plans for all possible scenarios integrated into a computer data bank. An expert system can then suggest the scenarios best suited to the event to be processed.

However, although these tools are necessary, they will never replace training and basic human factors such as the capacity for initiative and adaptation which remain fundamental for coping with a large-scale event.

Operating instructions, minimum operating conditions, emergency plans

Every tunnel operator produces and updates written procedures (sometimes called "Operating instructions") which define the objectives and criteria of possible actions by different internal service providers, which can affect the tunnel or road. All types of operational events need be taken into consideration for the procedures, including routine incidents, serious accidents and emergencies. The "Operating instructions" contain the basic actions to be carried out with associated procedures and existing constraints.

The operator's staff also needs an emergency plan for both intervention after a road accident and technical failure of equipment in the tunnel. This plan usually meets regulatory requirements and includes operational procedures and instructions involving, at minimum, the tunnel operators and the intervention personnel in case of an incident or technical failure. The emergency intervention procedures should be coordinated with those applied by emergency and rescue services. The detailed content of this plan could be defined by national instructions or directives specific to each country and needs to be tailored to the specific technical and organizational aspects of the tunnel.

Technical Report 2007R04 defines the organisation of operation in greater detail in chapter 4  "Operating staff: tasks and facilities"

Operational strategies for ventilation

The tunnel ventilation system should ensure adequate air quality during normal operation and maintenance activities, as well as providing the desired smoke management in case of fire. Moreover, the escape routes should be kept free from smoke.

However, when selecting and operating a ventilation system, normal operation and smoke management cannot be considered independently.

During normal operation, it is required to keep the pollutant level inside the tunnel below defined threshold values for visibility due to particulates, or toxic gases in each section of the tunnel. Some tunnel ventilation systems can be primarily designed and operated in order to minimize the impact on the environment at the tunnel portals. Further information on design criteria for normal operation can be found in the specific section of the page on "Design and dimensioning".

Control for normal operation should be achieved at minimal operating costs. It is conventional to control the operation of the ventilation system through measurement of the relevant pollutants (including opacity and either or both CO and NOx), to optimise the use of the system. In some cases, tunnel operators need to use SCADA systems to check the proper functioning of automatic control systems. For further information see the page on "Control and Monitoring".  

Other objectives are occasionally pursued e.g. to minimise the risk of condensation occurring on the windscreens of vehicles and preventing the entrainment of fog from outside the tunnel. For maintenance work in the tunnel, the tunnel ventilation has to ensure the air-quality criteria for longer exposure of workers.

In case of a fire in a tunnel, the ventilation system must be operated in order to establish and maintain appropriate conditions for self-evacuation and rescue operations.

During the self-evacuation phase (also called the self-rescue phase, during which tunnels users would, of their own volition, attempt to evacuate from the tunnel), the ventilation system aims to create and maintain a tenable environment for the evacuation of tunnel users. Specifically, this environment consists of acceptable visibility and air quality levels.

During the fire-fighting phase, the ventilation system operation has to be decided by the head of emergency operations, who should choose the best solution taking into account the possibilities of the ventilation system and the operational needs of the firemen.

Further information can be found in section 8.3 "Operation of smoke control systems" of the PIARC report 2007 05.16 "Systems and equipment for fire and smoke control".  

In contrast with normal operation, where conditions in the tunnel change rather slowly, the conditions during a fire may change rapidly, leading to deteriorating conditions within the tunnel. The designer initially defines the objectives of the ventilation system, sizes the necessary equipment and proposes what actions the operator should take under various scenarios. The designer, therefore, needs to understand the behaviour of the smoke, what the tunnel user might do (human behaviour), and what the operator, and later emergency services, should do in response to an emergency.

Different ventilation strategies may be used in tunnels. The choice between them is generally guided by fire safety considerations; the use of the system in normal operation is adjusted to suit.

The PIARC report 1999 05.05 "Fire and Smoke Control in Road Tunnels" provides extensive details on smoke management and PIARC report 2011 R02 "Road tunnels: Operational strategies for emergency ventilation" discusses different ventilation methodologies and operational strategies..

For tunnel operators this is reflected in a series of choices that can be made about the configuration of existing ventilation equipment. Usually these choices are based upon pre-planned equipment usage configurations, hence the following questions are to be considered:

• What is the intention of the design?
• How should the system be operated to achieve that intention?
• Independently of the design – what can the ventilation system achieve and how?

The objectives of the design should provide a useful means of characterizing the potential operational performance of the ventilation system, whereas the actual characteristics of the system define the achievable result from an operational perspective. In responding to a real incident this distinction may be critical – and the importance of the design-operator interface crucial.

In addition, it is essential to establish standard operating procedures for road tunnel fires. The development of an integrated Emergency Response Plan is an essential first step in planning the operational responses to tunnel emergencies. The plan should specify particular responses to various types of incidents, including the description of how the ventilation system should be used. For its preparation, a proper coordination and interaction between the tunnel designers (in some cases), the tunnel operators, and all outside agencies that might ultimately become active responders to an emergency incident within the tunnel, is required.

In the case of urban or complex underground systems, tunnel operators have to face additional challenges: during normal operation to properly control the fresh air flow inside the tunnel and make sure that all branches can received the required amount of air for pollutant dilution; and in case of incidents with fire, to minimise the harmful effects of smoke by isolating different tunnel sections to avoid smoke contaminating the whole tunnel network.

Further information on main issues related to ventilation of these tunnels can be found in chapter 6 "Ventilation" of the report 2016 R19 "Road Tunnels: Complex Underground Road Networks".  

Operational costs

Experience shows that a kilometre in a tunnel is always more costly than a kilometre of the same road outside. Underground structures require systems and equipment that ensure safe operation under normal operating conditions  and allow the protection and the evacuation of users and the intervention of rescue services in case of an incident, accident or fire. These facilities not only  involve considerable investment costs but also result in particularly high costs for operation and maintenance. Thereby the role of the operator is to ensure the continuity and the safety of operation in a context of controlled costs.

In all cases, even a high standard of tunnel operation may not allow an optimisation of operational costs, if the design and the construction of the tunnel have been undertaken to a low quality level. Operational costs therefore need to be a major  consideration during the different phases of the project and the work execution. Solutions need to be found well before becoming an issue during the operational phase.

Operational activities have to be organised at an adequate level in order to ensure that the expected lifecycle of the equipment  is met, without compromising mandatory operational performance requirements. The lifecycle of equipment in tunnels is normally shorter than in other environments, since the atmosphere in tunnels is particularly corrosive.

The Technical Report 05.06.B "Road Tunnels: reduction of Operating Costs" is entirely devoted to operating costs and in particular focuses on how to reduce them.

Staff-related issues

Tasks entrusted to the operating staff are essential  for safety and the overall efficiency of tunnel operation. Moreover, the context is evolving, with operational issues growing in importance and operating systems becoming increasingly complex.

The staff in charge of tunnel operation therefore need to satisfy the following requirements:

• They should be well selected through a recruitment process
• They should be well trained before taking up their functions
• They need refresher courses throughout their career
• They should participate in exercises, possibly organised in cooperation with external services.

During recruitment phases, the qualifications required for the future operators must be defined according to the nature of operational tasks.  Even if the tasks are similar in all countries, the people responsible for executing them do not necessarily belong to the same kind of organisation in each country. Nevertheless, the skills and aptitudes required should be similar.

While designing the staff training (initial or permanent), the following two issues need to be addressed:

• What kind of training needs to be provided to the operating staff (or, what should be the obligatory training)?
• What criteria are to be applied by the operations manager for validating the quality of the training and the results obtained?

If there are no national rules on the content of training, the operating body has to adapt its training programme to the specific characteristics and requirements of its tunnels.

The Technical Report 2007R04 "Guide for organizing, recruiting and training road tunnel operating staff" specifies the recruitment and training of personnel in greater detail, chapters 7 "Recruitment of operation staff" and 8 "Training operating staff" .

Feedback from operation and incidents

The collection of data regarding incidents and accidents and their analysis is essential both for the evaluation of the operation criteria and for the assessment of risks in the tunnel. All of this is important with a view to a continuous improvement in tunnel safety. In particular, the collected data enable the frequency of events to be evaluated. Data also provide feedback regarding the consequences of events and also the  effectiveness of safety measures and equipment. They also provide additional information on the real behaviour of tunnel users.

The collection and analysis of data regarding incidents and accidents should allow the following two objectives to be achieved:

• At a local level (i.e. at the level of each single tunnel): they form an important basis for the definition and evaluation of improvements, to be decided by the owner of the tunnel. They are also a decision-making aid for the general improvement of safety in a given road network;
• At a national and international level: they form the key basis for the reference framework allowing authorities to formulate and adapt the general policies related to tunnel safety. In particular, they allow an assessment of the magnitude (in terms of frequency and severity) of critical events that can cause a danger to the life of users. They also allow the efficacy of safety installations to be measured and in certain cases, a comparison of the level of safety in a given tunnel with national or international safety data.

Lastly, they provide information (national statistics according to the type of tunnel) that is useful for the analysis of risks relating tunnels that are in project stage (ie. in development) or tunnels under operation that do not yet have an adequate database.

The lessons drawn from the operation, particularly during incidents and accidents, should be analysed. In fact if the results of these analyses reveal deficiencies, there is an opportunity to intervene by improving strategies and/or operating instructions.

The Chapter 3 "Collection and analysis of data on road tunnel incidents" of Technical Report 2009R08 defines in detail the conditions for analysing data from incidents and/or accidents.

Operation during maintenance and refurbishment works

Maintenance tasks are not very different from one tunnel to another when there is similar equipment. However, some tunnels have specific features (dense and non-stop traffic, very long diversion route, etc.) that make total or even partial closures of the tunnel very difficult. In this case, the operator may have to maintain a certain operational level, while maintenance interventions are being carried out. This is possible only by deploying special measures that should take into account not only the safety offered to the users but also the safety of the maintenance staff.

Chapter 2 of technical report 2008R15 "Operation of existing urban road tunnels" defines the conditions for carrying out maintenance when the tunnel is in operation.

The same difficulties as those mentioned above are likely to be encountered during a refurbishment of equipment in a tunnel that cannot be closed down easily. With regard to maintenance interventions, this type of works may require several weeks, or even several months to be completed. Consequently, more elaborate (and often costlier) measures have to be planned.

Chapter 6 of technical report 05.13.B "Renovation of tunnels" discusses aspects relating to refurbishment.

Short tunnels and/or very low trafficked tunnels

The recommendations presented in the previous pages of the chapter "Operation" are not always relevant (or may be difficult to implement) for short tunnels, or very low trafficked tunnels, or tunnels located in remote areas with low population densities.

For these particular tunnels, it is recommended to carry out a detailed specific analysis for each tunnel (or group of tunnels located on the same road network), taking into account:

• geographical and climatic conditions,
• local or regional resources available in the vicinity: authorities, operator, emergency services, etc.,
• economic context,
• exposure to risk and level of risk.

This analysis will then make it possible to organise and to implement the most suitable operating system, according to the specific conditions of these tunnels.

Maintenance of equipment

Throughout the life of the tunnel, the operator should carry out both the maintenance of civil engineering works and the tunnel equipment. (See Report 05.13BEN "Good Practice for the Opereation and Maintenance of Roads Tunnels"). The maintenance of civil engineering structures is not described in this paragraph.

The maintenance operations on equipment can be classified into two groups:

• Preventive measures that are carried out at fixed intervals with the objective of maintaining the equipment in a good operating condition. Preventive maintenance offers the advantage of preventing, as far as possible, unforeseeable failures and is easy to plan in advance. It can however lead to high costs if the interventions are too frequent. They therefore need to be suitably optimised. There are two kinds of preventive maintenance: systematic maintenance and predictive maintenance.
• Corrective actions that are carried out when a system or a part of a system has failed or been damaged. Corrective maintenance offers the advantage of using a system to the maximum extent of its service life. Its disadvantage however, is that it cannot be planned and therefore emergency repairs are normally carried out with a significant surplus cost and consequences for the traffic flow.

It is recommended to use preventive maintenance where possible and for those systems that are not redundant and are related to safety. Preventive maintenance allows the joint planning of different maintenance tasks in the event of every closure of the tunnel to traffic. Moreover, it helps maintain the equipment in a good operating condition. It may be noted however that even when preventive maintenance is carried out very well, the operator cannot avoid corrective interventions. However, preventive maintenance will ensure costly corrective maintenance is kept to a minimum.

Usually the operator's staff do not carry out all maintenance tasks; the operator normally entrusts contractors and several options are consequently available:

• It is possible to contract only those maintenance tasks related to a specific technical level. The operator can thus contract tasks that present no technical complexity (cleaning, washing, ...) or it can contract only very complex tasks (supervision system, radio retransmission equipment, ...)
• It is possible to contract all tasks of one or more equipment groups (all ventilation systems, all remote surveillance installations, etc.).

Chapter 7 of Technical Report 05.06.B entitled "Cost of maintenance", chapter 4 of Technical report 05.13.B entitled "Maintenance and operation" and chapter 6 of Technical Report 2007R04 entitled "Organising operating staff", give more complete information on the subject of maintenance.

If they exceed a few hundred meters in length, road tunnels are to be provided with equipment for ensuring the safety of users under normal conditions or in case of disruptions to normal operation. Because of their involvement in the global safety chain of the tunnel, this equipment must be selected and designed with great care, with regard to maintenance, inspection and refurbishment. Hence a report has been produced to assist the operator or operating body with the issue of maintenance and technical inspection.

The technical report 2012R12EN entitled "Recommendations on management of maintenance and technical inspection of road tunnels" gives recommendations for the management of maintenance, essentially in the domain of equipment. The aspects relating to light civil engineering are listed and described only very briefly.

Life Cycle Cost (LCC) aspects have become an important issue for private tunnel owners, as well as government agencies. Sound knowledge of life cycles helps to optimise investment costs during the early stages of designing a system. It is also helpful in organizing the periodical maintenance of technical equipment. The technical report 2012R14EN entitled "Life cycle aspects of electrical road tunnel equipment" outlines how LCC aspects support the design of equipment as well as maintenance concepts. Bearing in mind that investment decisions are often technology-driven and that equipment costs have risen dramatically in the past years, the report helps to understand the life cycle process and the aging process of material. The report provides background knowledge on LCC aspects, which could be of use for further investigations. Specific focus is given to the surrounding ambient conditions, e.g. temperatures, which have a significant impact on the aging process.

Life cycle of tunnel equipment

The increasing variety of tunnel equipment means that life cycles may vary considerably from one type of equipment to another.

Some equipment may have a lifespan of more than 20 years (power supply, ventilation ...); others will only last a decade or so (notably equipment with a lot of electronics). For some, its lifespan may even be less than 10 years.

It is therefore essential to examine the lifespan of each family of equipment, with particular attention when this lifespan is low (10 years or less). The purpose of this review is to identify the factors that have a strong influence and that can be acted upon to ensure the lifespan of the product, or even improve it.

It is particularly useful to take into account factors such as temperature, humidity, mechanical stress and the environment.

A life cycle analysis can be conducted at different stages of the life of a tunnel (and its equipment):

• Preliminary design phase,
• Design phase,
• Construction and commissioning phase,
• Operation phase,
• End of operation phase.

Technical reports 2016R01 “Best practice for life cycle analysis for tunnel equipment” and 2012R14 “Life cycle aspects of electrical road tunnel equipment” provide further information on this issue.

Technical inspections

The equipment of a tunnel is highly varied. From electromechanical equipment (power supply, ventilation, lighting ...), to operating equipment using more recent technologies (video surveillance, SCADA, automatic incident detection...), it requires more or less frequent interventions to maintain functionalities.

Interventions to be performed on equipment can be grouped into three broad categories:

• Maintenance,
• Control,
• Renewal.

Maintenance can be defined as a set of actions that maintain equipment in a specified state, restore it to this state or ensure that it can provide a specific service. These actions can be preventive in nature (referred to as preventive maintenance) or remedial (corrective maintenance).

Maintenance control, in the broadest sense, aims at ensuring that the maintenance actions carried out allow satisfactory operation of the equipment and that the financial resources allocated are adapted to requirements.

An assessment can be carried out by conducting technical inspections at specified periods:  

• at commissioning of the equipment (initial inspection),
• during the tunnel operation phase (periodic inspections).

The initial inspection must be carried out before equipment is put into operation. It aims, on the one hand, to check the quality and performance of the installations and, on the other hand, to ensure that the tunnel and its equipment comply with regulations, in particular with regard to safety.

The initial inspection, which provides a reference on the condition and performance of the tunnel at commissioning, should be followed by further inspections throughout the tunnel’s life. These inspections must be carried out periodically at an interval that may vary from one country to another, but which is, in most cases, of the order of several years.

The results obtained during these various inspections therefore make it possible to verify that maintenance is well adapted and that the expenditure and financial budget  makes it possible to achieve the objectives set.

When the equipment approaches the end of its life, these inspections also enable refurbishment or renewal actions to be planned.

Further information on technical inspections can be found in technical report 2012R12EN: Recommendations on management of maintenance and technical inspection of road tunnels.

Maintenance of complex underground tunnels

1. Responsibility of each operator

2. Commitment of each operator in the context of the overall maintenance strategy

3. Coordination between the Operators

4. Sharing of best practices

Maintenance in complex tunnels is a holistic and interrelated issue where a contribution of one sector must be proactively complemented by the contribution of other sectors. The purpose of maintenance in underground and complex tunnel structures is to improve the serviceability of the infrastructure and to reduce operational costs. When maintenance is performed at the time of the tunnel life cycle it optimises the available equipment, minimises the risk of accidents and largely contributes to public safety. Tunnel operators, particularly those involved in the maintenance of large underground and interconnected infrastructures are reminded of the need to optimise their maintenance strategies and to enhance public confidence in the use of these infrastructures by making them safer, efficient and continuously available for use.

The strategic components related to maintenance in tunnel networks may be divided into four categories:

• The responsibility of each operator,
• The commitment of each operator in the context of an overall maintenance strategy,
• Coordination between the operators,
• Best practices to be shared.

1. Responsibility of each operator

Each operator is responsible for the safety level of its infrastructure, which contributes to the overall level of safety of the entire complex. Each operator is responsible for informing the lead operator of its maintenance demands and the demands of the others. A global maintenance coordination plan should be established among all operators and adjusted to the individual operators. Focus should be on global benefits and minimizing the time of restricted tunnel operations is essential.

At same time, each operator has responsibilities that may be impacted by actions of other operators. The Lead Operator of the underground tunnel infrastructure is responsible for the overall co-ordination and communication process.  

2. Commitment of each operator in the context of the overall maintenance strategy

Each operator is responsible for managing and maintaining its own equipment. Each operator must establish the list of equipment under its responsibility and share it with the other operators.

Some equipment could be considered as strategic equipment, necessitating collective responsibilities. The list of this strategic equipment must be established, discussed and shared. It has also to be clearly defined who is in charge of what.

It is crucial to acknowledge that the collective efforts of operators will trigger combined responsibilities for all participants in the process.

3. Coordination between the Operators

The coordination process in the context of the underground interconnected complex tunnels entails the following:

a) Organizational Behaviour

There is a need to develop group work which is only achievable if the organisational behaviour is aligned to the needs of the infrastructure (refer to Operation of complex tunnels).

b) Maintenance of one has implications on the others

• Where interfaces are unavoidable, it is important that each operator fully respects its obligations in a timely manner. This may have a direct impact on the road tunnel users and on the overall quality of service being offered to the public.
• Interfaces entail teamwork, proactiveness and compromise. No improvement works should be undertaken if they lead to complicated situations for other tunnel operators. 

4. Sharing of best practices

Best practices in tunnel maintenance will also require a coherent effort from the key players and stakeholders. This can be achieved by defining a set of principles and procedures set out in the operator’s procedure manual generally known as the inventory manual. Tunnel operators are encouraged to be acquainted with all key components of the inventory manual which are applicable to their functions and have been developed by PIARC over many years.

Winter maintenance

• 1. Introduction
• 2. Considerations
• 3. Problems, Preventive actions, Corrective actions and Constraints
• 4. Construction and design considerations
• 5. References
• 6. Presentations made during PIARC Winter Road Congresses

1. Introduction

Winter creates very difficult conditions for road tunnels. For example, under the effect of the cold, water infiltrations can produce cracks in the concrete, cause slabs to heave, make the pavement in the tunnel slippery or form icicles above the roadway. When water freezes, it can block or break drain pipes and render fire safety systems inoperative. Snow storms, hail and freezing rain make roads slippery and dangerous, particularly at the entrance and exit of tunnels (fig 1). The risk of an accident or pile-up therefore increases, and it is also more difficult for emergency services to get to the site of an accident, especially during peak traffic hours.

2. CONSIDERATIONS

The considerations that impact the winter serviceability of road tunnels are both numerous and varied. The operator, whose mission is to ensure user safety, must therefore make every effort to counter the adverse effects of winter as well as ensure that users benefit from safe conditions in circumstances that are sometimes very difficult, such as extreme weather events. The operator must adequately coordinate its tunnel de-icing and snow-clearing teams, which can be challenging and slow in busy traffic. Visibility in tunnels further decreases during the winter months, as lighting fixtures become dirty and due to the spray deposits along the walls, which also affect surveillance cameras and air quality sensors. The operator must assure the operational availability of all safety and fire protection equipment, which must also be protected from freezing.

Operational continuity is of the utmost importance for the operator. However, according to the nature of the problems experienced in winter, any major event forcing a closure or a reduction in operations will inevitably have repercussions on the entire network, resulting in socioeconomic costs related to delays and user complaints. More so than any other season, winter compromises operational continuity. A sound management of the network is therefore essential.

Communications make it possible to transmit information in order to facilitate the management of difficult situations. At all times, the operator must provide useful information to the media in order to quickly inform users of road conditions, closures and snow removal operations. In a transport organisation, efficient communications structured in a well-defined decision-making hierarchy make it possible to effectively manage extreme weather events that require major decisions, such as lane or tunnel closures, whether for safety reasons or de-icing operations.

3. PROBLEMS, PREVENTIVE ACTIONS, CORRECTIVE ACTIONS AND CONSTRAINTS

Table 1 below presents a list of the particular problems inherent to the winter conditions that road tunnel operators must face. It also presents a non-exhaustive list of preventive and corrective actions, in addition to the usual constraints that operators must deal with when conducting operations.

Table 1

Problem	Preventive actions	Corrective maintenance	Constraints
Water infiltration	- Program to identify and seal leaks and infiltration - Monitor waterproof joints	- Manage infiltrations - Install heated temporary pipes - Repair waterproof joints	- Maintaining traffic flow - Heavy traffic periods - Permit to close lanes temporarily for maintenance (closures usually at night or on weekends) - Difficult work conditions in road tunnels
Formation of icicles or stalactites		Locate icicles and stalactites and conduct de-icing operations as needed when user safety is compromised	- Availability of snow removal teams and equipment - Heavy traffic periods - Permit to close lanes temporarily for maintenance - Difficult work conditions in road tunnels
Frost or snow on the roadway - Unexpected slippery conditions in road tunnels - Motor vehicles and heavy vehicles have difficulty exiting tunnels during snowstorms, causing traffic slowdowns, traffic jams and accidents - Risk of skidding in sloped accesses, causing motorists to lose control, accidents	- Inspection of snow removal equipment after use and before storage - Application of de-icing agents when precipitations begin - Installation and use of roadway de-icing systems (heating cables, hydronic heating, etc.) at tunnel - Predictive diagnostics to preheat equipment that is sensitive to extreme cold	Remove and transport snow and apply de-icing agents (abrasives are to be avoided as they can block drain pipes)	- Budget - Availability of snow removal teams and equipment (24/7) - Heavy traffic periods - Permit to close lanes temporarily for maintenance - Restrictions on the use of de-icing agents (environmental impact, toxicity, storage and application precautions, recovery, transport and destruction) - Efficiency of de-icing agents relative to temperature - Risk of damage to the concrete structure caused by de-icing agents (e.g. salt).
Debris and formation of ice in drain pipes	- Periodic inspection program - Clean pipes, bore holes as needed - Verify the operation of heating cables - Monitor low temperature alarms in protected systems	- Flush pipes - Remove ice in gutters - Bore holes in pipes as needed - Replace defective drainage components	- Maintaining traffic flow - Heavy traffic periods - Permit to close lanes temporarily for maintenance (closures usually at night or on weekends) - Difficult work conditions in road tunnels
Accumulation of dirt on tunnel walls, ceiling and equipment, such as surveillance cameras, lighting fixtures, air quality sensors, signalling equipment, escape route indicators, etc.	- Visual inspections - Maintenance operations, including cleaning surveillance cameras, walls and lighting fixtures outside busy traffic hours	Maintenance operations, including cleaning surveillance cameras, walls and lighting fixtures outside busy traffic hours	- Low temperatures - Heavy traffic periods - Permit to close lanes temporarily for maintenance - Restrictions on the use of cleaning products (environmental impact, toxicity, storage and application precautions, recovery, transport and destruction) - Efficiency of cleaning products relative to temperature - Difficult work conditions in road tunnels
Corrosion of doors, anchors, equipment, cable and equipment mounts	- Use of products and materials that are compatible with the aggressive environment in tunnels - Periodic inspection program - Use of stainless steel or composite components where applicable - Inspection and maintenance operations, including lubrification and/or rust protection	Replace rusted components and equipment as needed	- Standards applicable to road tunnels - Resistance to fire, water, humid and corrosive environments
Cracking, fragmentation of concrete debris falling on the roadway, heaving of concrete slabs, contamination of concrete	- Waterproof membranes - Protective coatings - Periodic inspection program with damage and contamination surveys - Surface repairs	Repair the concrete Seal cracks Rehabilitate the infrastructure	Budget Permit to close temporarily for inspections Maintaining traffic flow during work Degraded modes of operation Measures to reduce impact on users Difficult work conditions in road tunnels
Increased energy consumption during winter, peak power demand  and impact on the electricity network Uneven  between seasons and impact on billing	- Analyse and follow up energy consumption and peak power demand - Intelligent energy management system and measures to reduce demand - Selection of energy-efficient equipment - Use of alternative energy sources where possible and cost-effective - Storage of energy during low consumption periods to balance energy use - Technological watch		- Budget and cost-effectiveness of performance-enhancing solutions - Availability of space for required equipment (e.g. storage) - Availability of alternative energy sources - Resistance to changing operational and energy consumption habits - Laws, regulations, political pressure, sustainable development
Erratic operation of electronic equipment due to cold and humidity	- Use of products that are compatible with the cold, humid and aggressive environment in tunnels - Monitor alarms - Periodic operational tests and calibration		- Permit to close temporarily for inspections - Maintaining traffic flow during work - Degraded modes of operation - Measures to reduce impact on users - Difficult work conditions in tunnels

4. CONSTRUCTION AND DESIGN CONSIDERATIONS

Usually, the construction of roads through mountain ranges may require tunnels at high altitudes. Above 1.000 meters over sea level, special maintenance activities are required to provide acceptable traffic conditions inspite of the risk of snow or ice formation. This situation becomes critical in the proximity of tunnel portals.

At the north of the province of Huesca, in Spain, where several tunnels above 1.100 meters above sea level can be found, several important factors are to be considered to deal with temperatures which can go below -20ºC.

Water is the hardest enemy to fight: causing infiltration due to low temperatures, producing cracks and even spalling in vaults and side walls.

At the tunnel portal, an adequate construction of pavement and good quality of road painting are key factors for their durability. High quality materials are required because snow plough circulation and extreme meteorological conditions can cause their deterioration.

To fulfil the requirements of Rd635/2006, the transposition to the Spanish law of the European Directive 2004/54 on minimum requirements for road tunnels safety, several types of equipment must be installed which can be severely affected by malfunctioning or even breakdowns when needed.

Suspended power supply lines are exposed to ice formation which is the origin of outages which, if regular, can affect the durability of UPS and diesel generators.

Water tanks to supply fire hoses of the tunnel must be carefully constructed to avoid the appearance of cracks. In addition, continuous water circulation is advisable.

Water supply pipes must be protected with thermal protection and, if possible, emptied. Opening elements of fire hydrant and hoses can be also affected and the technical rooms containing pumping machinery should be above 0ºC.

In addition, proper maintenance of the vehicles used for operational and emergency purposes is crucial, including the use of adequate antifreeze products for motor and fuel and water tank protection.

And last but nor least, both the difficulties in the relief of the operation staff and appropriate clothing (not only warming or waterproof aspects but also visibility improvement) must be considered.

5. REFERENCES

1. DEBS A., "Challenges related to winter operations in urban highway tunnels», reference RR361-076, AIPCR, 2014
2. LÓPEZ GUARGA R., "Proyecto de las Instalaciones y Equipamientos del túnel de Somport. Parte española", Ministerio de Fomento, 1996
3. DEBS A., "Winter operation of road tunnels in Quebec. The Ville-Marie and Louis-Hippolyte-Lafontaine tunnels", International Winter Road Congress, Quebec, 2010.
4. V. LANGNER, B. HAGENAH, GRANER GUNBH (Autriche), T. CRONVALL, VR TRACK OY (Finland), "Ice formation. Aspects of planning and measures for climate impact", 15° International Symposium on Aerodynamics, Ventilation & Fire in Tunnels, Barcelona, September 2013.
5. Agencia Estatal de Meteorología. Datos estadísticos

Maintenance and monitoring of civil works

 

 

 

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General planning

Due to the amount of technical equipment in an urban road tunnel it is of utmost importance to keep all documentation about the equipment up to date, not only after major refurbishments, but whenever a change is made.

A refurbishment usually requires updating documentation of:

• Technical details of the tunnel and equipment;
• Procedures for normal operation;
• Procedures and scenarios for emergency response;
• Procedures for inspection and inspection frequencies;
• Procedures for maintenance and maintenance frequencies;
• Procedures for education, training and exercise.

When planning a major refurbishment it is recommended to use the same approach as for a new design.

General recommendations on refurbishment can be found in the PIARC Report 2008R15EN "Urban road tunnels : recommendations to managers and operating bodies for design, management,operation and maintenance".

Safety issues

If the tunnel design and equipment no longer fulfil the requirements of the operator, the tunnel users or legislation, it may be necessary to refurbish and/or upgrade the tunnel.

During refurbishment or upgrading, it is important to:

• maintain a minimum safety level for the traffic,
• ensure the safety of personnel working in the tunnel,

Safety of both workers and tunnel users can be influenced by completing refurbishment/upgrading activities in the shortest period possible and every effort should be made to avoid delays in the progress of work.  Well planned and efficiently implemented works can effectively reduce the length of these periods.

For both tunnel users and workers, total closure of all tunnel tubes during refurbishment/upgrading obviously provides a much higher level of safety. Workers are protected from traffic and teams can work on all facilities throughout the full length of the tunnel. For traffic, accident risks linked to the implementation of temporary traffic control measures within the tunnel are avoided.

In certain cases it is impossible to close the tunnel entirely. For instance, if the tunnel is the only reasonable means of crossing a strait or a mountain ridge, where alternative routes are not possible, not practicable or very expensive. In these cases refurbishment/upgrading of structures and installations have to be performed while the tunnel remains in service.

Partial closure of one or more lanes is possible during refurbishment/upgrading activities, but working in a tunnel while traffic is present is dangerous for the personnel and requires specific measures to protect them (e.g. the construction of temporary barriers to separate workers from the traffic).

In twin-tube tunnels, one tube can be closed for refurbishment while bi-directional traffic flow is allowed in the other tube. However, this solution is far from ideal and should only be adopted if it is not possible to divert traffic onto an alternative route. Whilst it obviously protects the safety of workers, this situation leads to the users driving in opposing directions within a tube where they are accustomed to traffic moving in only one direction. This can induce a potential increase in accident rates and should be avoided in heavily trafficked tunnels. In tunnels with low to moderate traffic, the risk of accidents can be reduced by the use of VMS and overhead lane control signs. In the case of three-lane tubes, the centre lane should, if possible, be kept free of traffic and act as a buffer safety zone.

In all cases where there are plans to alter the usual traffic configuration in a tunnel, additional safety measures should be implemented: reduced speed limit, closure of slip roads in the vicinity of the tunnel and the implementation of safety exercises in collaboration with emergency services under similar “works” conditions.

Finally, each time the lane/tube/tunnel is reopened to traffic following a closure, great attention must to be given to clearing and cleaning the road to prevent accidents caused by tools and materials in the tunnel or on the road. Similarly, any temporary or uncompleted works must be satisfactorily secured and made safe for the following operating period.

Additional information on refurbishment/upgrading can be found in chapter 6 "Renovation of tunnels" of technical report 05.13.B. 

Environmental QUESTIONs

Tunnel refurbishment/upgrading should be conducted in such a way that the negative impact on the environment is as low as reasonably practicable. This can be obtained by:

• requesting that selected suppliers apply a sustainable process for building material production and means of transport,
• reducing the distance required to transport materials to the tunnel,
• favouring materials which have the lowest carbon footprint, or by recycling materials already used elsewhere.
• installing energy-friendly equipment, etc.

Tunnel refurbishment/upgrading can in many cases provide an opportunity to improve the environmental impact of the infrastructure as a whole, either through changes to the tunnel’s design or to its equipment.

In terms of design, an example of a major refurbishment project conducted with environmental issues in mind is the Croix Rouse tunnel in Lyon (France). In order to upgrade the tunnel’s safety standards, the initial tube has been linked to a new parallel escape gallery via cross-passages every 150 metres, thereby enabling the evacuation of users. The tunnel owner wished to give additional functions to this escape gallery by allowing its use by public transport (buses) and environmentally-friendly modes such as pedestrians and cyclists. This is an interesting example of the sustainable use of infrastructure for purposes other than those for which it was initially intended.

In terms of tunnel equipment, refurbishment/upgrading can provide an opportunity to reduce energy consumption. The main energy-consuming families of equipment in a tunnel during normal operation are lighting, ventilation, safety devices (signalling, closed circuit television CCTV, etc.) and pumping facilities (in subsea tunnels or when there is water seepage). The respective share of each of these energy-consuming systems varies greatly, depending on the specific characteristics of the tunnel: length, gradient, water ingress, etc. In terms of optimization during refurbishment/upgrading, lighting and ventilation systems are those which provide the highest potential energy savings.

Actions taken on lighting during refurbishment/upgrading are primarily designed to better define the lighting requirements in the entrance zone, which is the most heavily lit. Solutions implemented may:

• provide light sources other than through lighting devices;
• vary the level of lighting provided by devices to adapt it as much as possible to requirements linked to external light conditions
• adapt the level of lighting in the entrance zone to the average speed of traffic (e.g. in case of traffic jams) or to the variable speed limit of the traffic
• use more efficient dimming systems (e.g. LEDs, which allow a total and quick variation of light)
• use new lighting technologies, like LEDs sources

Other actions may concern the optimization of interior zone lighting. At the moment, most experiments, and in some cases test sites, involve the use of LEDs (light emitting diode) sources.

An example of energy-saving measures implemented to ventilation during refurbishment/upgrading is the installation of jet fans with inclined outlets. It has been shown that these jet fans can enable a significant improvement in the in-tunnel thrust obtained and a reduction in energy consumption.

Outside air quality (at tunnel portals or vitiated air extraction systems) can be improved during refurbishment/upgrading, through increased stack heights or by the installation of vitiated air treatment systems (air cleaning systems). In some countries, vitiated air treatment systems have been put in place (Spain, Japan, Italy, Norway France….). However, after some years of use, the conclusions regarding the efficiency of air cleaning are different from one country to another. The decision to use such systems therefore has to be carefully analysed, taking into account several criteria (investment costs, efficiency, maintenance, etc.).

Finally, tunnel refurbishment or upgrading can provide an opportunity to assist in the preservation of the animal species living around the tunnel. Measures that can be implemented include restoring passageways for certain species or preserving reproduction areas.

General environmental questions related to the design, construction, operation and refurbishment of tunnels are dealt with in the technical report 2017R02EN “Road tunnel operations: First steps towards a sustainable approach”.

Questions relating to the tunnel impact on outside air quality are dealt with in report Technical Report 2008 R04 "Road Tunnels: A Guide to Optimizing the Air Quality Impact upon the Environment".

Construction site organization

 

 

 

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traffic Management

Tunnel refurbishment or upgrading may require:

• total closure of the tunnel during the entire duration of the works,
• total closure of the tunnel during periods of low traffic (nights, weekends….),
• partial closure of one direction for a single tube tunnel or one tube for a twin-tube tunnel, potentially with alternate traffic
• partial closure of one or several lanes in the tunnel (in one direction or in one tube).

If possible, total closure of the tunnel for refurbishment/upgrading is strongly recommended during the entire duration of the works as it undeniably provides the best solution in terms of safety for both workers and users. When possible, it is better to implement closures over short periods and during low traffic (night, weekends etc.).

However, these two solutions mean that a deviation route becomes obligatory and the impact on a given road network can be considerable, especially in urban areas.

Depending on local circumstances, the traffic diversion route may be very long. The risks and costs of a long detour over a short period must be balanced against the risks and costs of a partial tunnel closure over a longer period. It is possible to calculate the costs of detours, including the extra kilometres and delays, to back-up and/or support a decision. Any planned closures must be coordinated in advance with the operators of the roads used for rerouting traffic.

If it is technically possible, if the traffic is low and diversion roads are not practical, an alternate traffic system may enable the tunnel to remain open.

In the event of closure, good advance preparation is essential and can significantly reduce disruption. Regional and/or nationwide publicity in advance of the closure is important (e.g. television, radio, internet, billboards, publication of telephone numbers for information and complaints).

Once the tunnel is closed, diversion signs and signals should be used to provide information to users as far upstream as possible, before the relative points of choice, which are sometimes located at a considerable distance from the tunnel. For users who are relatively close to the tunnel, they must be informed of the closure and the alternative route before the last point of choice.

When it is inevitable that refurbishment/upgrading work must be carried out while traffic is present, specific traffic management measures must be adopted upstream from and inside the tunnel. In tunnels with two or more tubes, it is possible to close a tube completely and either establish bi-directional traffic in the other tube or establish a deviation route for users of the closed tube. If bi-directional traffic is established in the other tube, there is less inconvenience to users, as they do not have to take a deviation route. However, in terms of safety, this solution is far from ideal (and should be avoided in heavily trafficked tunnels) since it leads to users driving in opposing directions and hence an increased risk of accidents. This risk can be reduced by the use of VMS and overhead lane control signs. In the case of three-lane tubes, the centre lane should, if possible, be kept free of traffic as a buffer safety zone. Additional traffic management measures such as speed limit reductions and the implementation of an obligatory distance between vehicles should also be envisaged.

Where a tube is not completely closed to traffic and simple lane closures are implemented, they should always start before the entrance portal. Traffic should first be merged into the slower moving lane, then moved to the lane available at the incident site before entering the tunnel. In urban tunnel approaches this may not always be possible. Preferably lane closures should run for the full length of the tunnel. A situation where traffic is required to change lanes inside the tunnel is generally not recommended. However, in the case of longer tunnels, it may be advantageous to allow traffic to diverge and use all lanes once clear of all of the work sites. A risk assessment can result in the safest method for the situation.

Once again, additional traffic management measures such as speed limit reductions and the implementation of an obligatory distance between vehicles should also be envisaged.

Addition information on traffic management measures during tunnel closures can be found in PIARC report 2008R15EN: “Urban Road Tunnels: Recommendations to Managers and Operating Bodies for Design, Management, Operation and Maintenance”.

Ventilation issues

Following construction, the unavoidable deterioration of tunnel ventilation equipment reduces the ability of the system to maintain the required safety and performance levels. In addition, new safety measures may be required for technical reasons or because of changes in the tunnel environment.

Appendix A.5 "Ventilation systems" of the PIARC report 2012 R20 "Assessing and improving safety in existing road tunnels" identifies some examples of weak spots for existing tunnels, explaining why it is often necessary to make modifications to the ventilation systems of existing tunnels, including among others the following:

• Modifications of the applicable regulations,
• Changes in the type of traffic, either due to an increase in the number of vehicles, or due to a change in dangerous goods traffic,
• New construction of infrastructure close to the tunnel, which influence its safety or operating procedures. 

In addition, chapter 6 "Ventilation" of the PIARC report 2016 R19 "Complex Underground Road Networks", explains the reasons that make the refurbishment of the ventilation systems of the complex networks considerably more complicated than in conventional tunnels and section 3.1 "General aspects relevant for design and refurbishment" of the PIARC report 2008 R15 "Urban Road Tunnels: Recommendations to managers and operating bodies for design, management, operation and maintenance" explains some general aspects that also impact the capacity to conduct refurbishment programs for this kind of infrastructure.

Tunnel impact on outside air quality

In the field of road tunnels, air quality is traditionally considered in relation to the level of concentrations of vehicle exhaust inside a tunnel. However, the concentrations of pollutants outside a tunnel can be harmful or annoying to people. Such pollutant concentrations rapidly reduce from a portal or exhaust shaft to the surrounding environment according to complex mechanisms such as the speed and direction of the wind and the neighbouring topography. Consequently, it is recognized that air quality in the vicinity of tunnel portals or other exhaust points is of interest when the traffic intensity increases and when tunnels are constructed in an urban environment.

Above a tunnel, the air quality is expected to be better than if an open air road section was situated at the same location. However at the portals and shafts, polluted air is set free when a longitudinal or transverse airflow is discharged by the piston effect of traffic and/or by ventilation systems.

Depending upon background concentrations and other sources localized close to a tunnel portal or shaft, the concentration levels of pollutants can exceed the maximum levels set by authorities. In that case measures must be taken to improve the air quality in the vicinity of the tunnel. Measures may include civil or mechanical works, planning of the land use around the tunnel, etc. Most often it may be possible reduce the pollution concentrations based on operational measures such as changes in the ventilation regime. Chapter III “Environment” of the 1996 PIARC report 05.02 “Road Tunnels: Emissions, Environment, Ventilation” provided background information on the behaviour of a tunnel air jet from portals.

PIARC has published the Technical Report 2008 R04 "Road Tunnels: A Guide to Optimizing the Air Quality Impact upon the Environment", which focuses on outside air quality related to tunnels and it is a guide to enhancing the urban environment by altering the emissions from vehicles and changing their spatial distribution within the space surrounding a tunnel. The guide considers a wide range of design and operation opportunities to mitigate the impact of tunnels on outside air: from the selection of the most optimum location of a tunnel, to gradients, ventilation type, air discharge management, traffic management, tunnel maintenance and finally (if still useful) contaminant removal techniques (see also Section 4.4.5 "Air cleaning" of the PIARC report 2017 R02 "Road Tunnel Operations: first steps towards a sustainable approach").

The environmental issues linked to ventilation, besides the energy consumption and the related carbon footprint, are linked to the localised, concentrated discharge of polluted air from the portals and stacks. Reducing their impact on the tunnel surroundings is part of good environmental design : see Section 4.3. "Tunnel air dispersion technique", Section 4.6. "Operational aspects" and Appendix D. "Overview of dispersion modeling in designing ventilation systems" of the PIARC report 2008 R04 "Road Tunnels: A Guide to Optimizing the Air Quality Impact upon the Environment".

Additional information specific for complex tunnels can be found in section 8.1 "External Air Quality" of the PIARC Report 2016 R19 “Road Tunnels: Complex Underground Road Networks”.

Noise and vibration

Noise is generally regarded as one of the key nuisances perceived by humans, which can significantly affect urban areas. It should therefore be taken into account in the design of tunnels, especially for those urban tunnels that have a high concentration of acoustical receptors in the immediate vicinity of portals and shafts.

Traffic-generated noise is not specific to tunnels. Underground infrastructures are generally regarded as having a positive influence on the acoustic environment, but there might be specific issues near the portals in some configurations. In most developed countries, noise impact studies are performed for every new infrastructure project (or significant modification), and the existence of tunnels is, of course, to be taken into consideration.

The main source of noise impacting the environment surrounding tunnels is the traffic. Part of the noise from vehicles running inside tunnels is reflected by the tunnel lining and reaches the portal that itself becomes a source of noise. Under certain conditions the noise level near the portal of a tunnel can be higher than the noise level of a related open air section. However, this kind of effect is significant only for those acoustic receptors lying in the immediate vicinity of the tunnel portal. Moving away from the portal, noise levels rapidly diminish, since the noise coming from the tunnel is attenuated by the prevailing effect of noise generated by vehicles in the open air sections.

There are also sources of noise that are associated with the tunnel infrastructure, the main one of which is the ventilation system. In the case of transverse ventilation, or longitudinal ventilation with extraction shafts, fans and air flow through inlets and outlets may generate significant noise, and in some cases they have to function even at night time when noise environmental standards are set at lower targets. One solution may be to reduce the use of the ventilation system by optimising its control, but this can only be achieved to a limited extent.

The most effective solution is to take these problems into account at the design stage. Considering that the most prominent noise effects are geographically limited, air inlets/outlets may be located as far away as possible from neighbouring buildings, but this may result in significant increases in cost. The air velocity should be kept at relatively low values at air inlets/outlets to reduce noise generation by making the size of these openings large enough. Additionally, silencers are most often necessary to prevent the noise generated by the fans from "leaking" out of the ventilation plant.

In the case of longitudinal ventilation, the noise impact from fans on the environment is generally moderate because, on the one hand, jet fans should not be located too close to the portals for maximum efficiency (consequently the noise of fans is "diluted" within the traffic noise), and on the other hand, silencers are usually fitted to the fans to maintain an acceptable noise level inside the tunnel. However, for particularly sensitive configurations, it might be necessary to select specific designs or operational measures.

Traffic-generated vibration is rarely a significant issue in the operation phase of a road tunnel (unlike rail tunnels, because trains generate much more vibration than road vehicles). Should such a problem occur, there is generally little that can be done apart from prohibiting access to the heaviest vehicles. Another source of vibration is the fans. These should be carefully balanced to avoid excessive vibration. However, fan vibration is generally not perceivable in the environment; it primarily affects the machine itself, and can compromise its longevity. It can also become a safety issue because jet fans, for example, may lose parts or even fall down from the tunnel ceiling due to excessive vibration. Vibration monitoring is crucial for the reliability and safety of jet fans.

Vibration is much more problematic during the construction phase, especially when explosives are used. Tunnel construction and related environmental measures are outside the scope of the PIARC committee on road tunnel operation; specific recommendations are published by the ITA.

Water impact

The impact of road infrastructure on water quality can be very significant during both normal operation (leaking of hydrocarbon products, tyre wear, etc.) and accidental situations (spilling of large quantities of pollutants).

The existence of a tunnel does not change the problem very much. As on any road, there is a need for water treatment (decanting, removal of pollutants) before releasing it into the environment. A few tunnel-specific facts should however be taken into account when designing water management systems. First, tunnels need to be cleaned on a regular basis, as often as every month for heavily trafficked urban tunnels. This generates large amounts of waste water containing cleaning products. Second, tunnels in which dangerous goods transports are allowed are generally equipped with specific gutters in order to limit the spread of flammable liquids on the pavement. If an accidental spill occurs, the flow rate of pollutant liquid in these gutters may be higher than what is encountered on a regular road surface, and the water management system should be capable of coping with these flow rates.

Very challenging issues related to water may be encountered during the construction phase in sensitive environments, for example regarding the turbidity of the construction site effluent. Appropriate measures should then be taken. In some cases, they represent significant constraints and cost for the construction works. Tunnel construction and related issues are outside the scope of the PIARC committee dedicated to road tunnel operation. The reader is therefore encouraged to consult ITA recommendations for further details.

Water impact is another aspect that has to be analysed during the life cycle of an infrastructure as tunnel.

Most of the impact of tunnels on water (and water on tunnels) happens during their construction, but some of the impacts remain for a long time and can become a hindrance to the tunnel operation and maintenance. Due attention must be given to these processes during the tunnel planning and design stages, in order to avoid adverse, and costly, consequences. Detailed investigation of surface and subsurface hydrology should take place before and during construction. The least damaging route (and structural elements) should be chosen to obtain minimum interruption and alteration of hydrological patterns and processes.

Theoretically, tunnels can be: impermeable (allowing no ingress of water and developing the full water pressure on the lining), permeable or semi-permeable (allowing some ingress of water and avoiding the development of full water pressure on the lining). In practice most tunnels are permeable during their construction and impermeable or semi-permeable during their operation. As a general rule water ingress into road tunnels are normally not accepted as it may have severe impact on the tunnel structure and in special cases can cause severe deformations, displacements, settlements and unwanted stresses leading to deterioration and in worst case collapse of tunnel walls and ceiling (bursting and squeezing of bare rock as well). For mechanical and electrical installations it may impact their functionality and lifetime expectation.  

Minor water ingress is tolerated if it can be completely controlled. This covers  tunnels located in specific rural areas and with extremely low traffic. This has been done in several locations in the period 1970 to 2000. In recent years,  rock tunnels have been constructed a with semi- or full inner-lining due to experience with tunnel collapses etc.. As a general rule (see national and international standards, codes etc.), all tunnels nowadays are designed with waterproofing systems to be delivered as completely waterproofed tunnels.

In unlined tunnels (or with a permeable lining), water ingress can be important. Fig. 2 shows water flowing through a permeable basalt layer in Canada.

The drying up of groundwater levels caused by the manner of building infrastructure is a topic which is becoming more and more important. The effect usually does not finish during tunnel operation, and the groundwater original levels almost invariably go down, with an irreversible impact on water supply wells.

The water entering a tunnel can dissolve the free lime hydroxide in the concrete lining, becoming more alkaline and releasing solid deposits in the drainage systems. This effect is more frequent in old tunnels with out-dated drainage systems. Fig. 3 shows drainage water flowing and lime calcium hydroxyls precipitating in a concrete lined tunnel. Fig. 4 shows a similar effect in a construction joint.

Sustainable tunnel operation

Road operators and road authorities are increasingly expected to promote an efficient use of energy and to adopt sustainable methods for the construction and operation of public roads.

Throughout its history, PIARC has published several reports aimed at improving the efficiency of tunnel operations, reducing operating costs and mitigating environmental impacts.

With the world population increasing, and several natural resources running scarce, sustainable development has justifiably become a topic of interest in various domains of society over the past decades. The field of infrastructure is no exception.

However, within this field, there are few guidelines and best practices available that specifically address the sustainability of road tunnels.

Moreover, so far, the World Road Association has not issued any recommendations for road tunnels which reflect the current ‘state of play’ in various countries. This is understandable, as road tunnels are just a small part of the road network as a whole. On the other hand, given that road tunnels are complex and expensive objects, with a life cycle that normally spans more than 100 years, it is clear that the concept of sustainable road tunnel operation is of great relevance.

The technical report 2017R02EN "Road tunnel operations: first steps towards a sustainable approach" was therefore developed as an initial means of making up for this shortfall.

Sustainable energy consumption

Optimizing the operating costs of a tunnel and in particular those related to energy consumption, is a task that must be undertaken from the early stages of the tunnel design. PIARC has shown that a significant part of operating costs is determined by the choices made during the design and implementation phases (Report 05.13.B Good practice for the operation and maintenance of road tunnels). 

It is also important to adopt a global approach that takes into consideration the three pillars of sustainable development: societal, environment and economic (report 2017R02EN: Road tunnel operations: First steps towards a sustainable approach). More specifically, it is important to avoid implementing a solution that is advantageous in terms of initial investment, but which entails an excessive annual energy consumption.

This naturally leads to applying an approach based on the cost of tunnel ownership as a whole, taking into account not only the initial cost of equipment, but also operating costs throughout the tunnel’s expected lifetime (Report 2016R01EN Best practice for life cycle analysis for tunnel equipment).
 
As the equipment present in tunnels is numerous, diverse and has lifespans that vary considerably from one type to another, it is often more efficient to conduct a specific optimization approach for each large family of equipment.

Finally, although, as we have said, the optimization work must be started during the initial design phases, the technical provisions chosen and the equipment implemented require constant monitoring, if they are to maintain their performances over time. Regular and thorough maintenance is therefore necessary so that all the actions undertaken to optimize the energy consumption of a tunnel remain efficient (Report 05.13.B Good practice for the operation and maintenance of road tunnels).