OPERATION

In order to successfully and efficiently operate and manage a road tunnel, operational tasks and the responsible body for carrying them out, need to be established in order to ensure that all actions required are handled in a consistent and safe way (see page on Operational tasks). The level of safety provided for tunnel users is highly dependent upon the specific characteristics of the tunnel, but it also depends strongly on operational procedures and the people who are in charge of the tunnel.

The people in charge do not necessarily need to belong to the same organisation: stakeholders and roles can be quite different. For example, the traffic police are normally in charge of traffic, but the task is sometimes carried out by a road administration, and in some cases, several tasks are entrusted to a private company/operator. Moreover, the same task (for example: traffic management) can be performed by many different bodies (operating staff, police, subcontractor), so the relative roles and responsibilities have to be specified as well as recommendations to improve the behaviour of people involved in tunnel operation and their level of cooperation (see page on Stakeholder cooperation).

In each case, the organisation of the operation and coordination with all the different bodies must be defined by written procedures and protocols that are simple and straightforward, so that they are clearly understood by all parties and are robust under pressure in emergency situations.

The organisation of operation can be quite different from one tunnel to another; consequently it is difficult to define an overall common framework. However, it is convenient to assess for each tunnel or group of tunnels the most suitable organisation to be adopted both during standard operation and in the event of an emergency situation (see page on Organisation of operations).

Specific organisational and operational procedures are often required for complex tunnels and underground road networks. The following types of tunnels may be considered as “complex”:

• A sequence of successive tunnels,
• Multimodal tunnels,
• Tunnels giving access to business and commercial centres (for public access and freight delivery). These infrastructures usually comprise a multitude of interfaces between numerous operators which represents a significant part of their complexity,
• Tunnels with a dual function as transit and access to underground car parks,
• Tunnels with reduced vertical clearance,
• Underground infrastructure with numerous entrances and exits, as well as underground interchanges.

All the above-mentioned infrastructures share several similar characteristics:

• Their complexity,
• Their location - essentially in urban and suburban areas,
• Their numerous interfaces with other infrastructures or neighbouring networks to which they are connected, thus creating as many interactions between the operators of various infrastructure and networks.

More information on such infrastructures, with specific case studies, can be found in the PIARC technical report 2016R19EN Road Tunnels: Complex Underground Road Networks.

Moreover, it is essential to establish standard operating procedures as well as minimum operating conditions and emergency plans. This is in fact a key step in planning the operational response to possible tunnel emergencies for which there need to be appropriate specific responses to various types of incidents (see page on Operating procedures).

Ventilation strategies must also be defined right from the design stage. Different strategies are possible. The longitudinal strategy consists in creating a longitudinal air flow in the tunnel, in order to push all the smoke produced by a burning vehicle onto one side of the fire. If users are present on that side, they may be affected by the toxic gases and reduced visibility, so the use of this strategy in bidirectional and/or congested tunnels requires great caution. The minimum air velocity for successful smoke control depends on the design fire size and tunnel geometry (slope, cross-sectional area).

The transverse strategy takes advantage of the buoyancy of fire smoke: smoke tends to concentrate in the upper part of the tunnel space, from where it can be mechanically extracted. The system is designed so as to preserve a fresh air layer in the lower part of the cross-section (correct visibility, low toxicity) which allows self-evacuation. It is therefore important to keep the longitudinal air flow as low as possible in the fire region to avoid de-stratification and excessive longitudinal spread of smoke. This strategy is applicable to any tunnel, but the design, construction and operation of the system are more difficult and expensive.

The choice of ventilation strategy is generally guided by fire safety considerations (see chapter 5 of report 05.05.B 1999 "Ventilation for fire and smoke control"

The management and day-to-day operation, as well as the maintenance of a tunnel, involve high operational costs and funding requirements. In fact, tunnels are among the most costly parts of a road network to be operated (in terms of energy requirements, staffing and monitoring). The definition and optimisation of the different cost elements in a tunnel and appropriate recommendations to reduce them have been analysed by the PIARC tunnel committee. The efficient use of energy and the progressive reduction of energy consumption should be considered, with a view to delivering a sustainable operation of the road network (see page on Operational costs).

The final objective is clearly to guarantee an appropriate level of service and quality to the users. The achievement of this objective obviously depends on the nature and overall performance of the facilities and equipment. The performance of the equipment often depends on how this equipment is operated by the tunnel staff in terms of timeliness and appropriateness. Therefore the staff called to perform operational tasks must be well selected when recruited, well trained before starting their tasks and continually throughout their careers (see page on Staff-related issues).

The safety level and the traffic capacity in a tunnel are influenced by changes characterising the road network and the evolution of the traffic itself. The tunnel operator may occasionally need to make minor or major changes to the system or to the management criteria to cope with these changes. It is therefore necessary to monitor changes and accidents using information and feedback, to continuously and systematically improve tunnel operations.

The operator needs to receive feedback from actual operation experiences, which can be analysed and used to propose improvements (see page on Incident Feedback).

When the tunnel equipment no longer satisfies the needs of the operator, the requirements of legislation or when the nature or the level of traffic changes, it may be necessary to upgrade or refurbish the tunnel. For the refurbishment of an existing tunnel, recommendations mainly concerning measures to facilitate the management of the traffic network. Equipment reliability and durability and whole life costs also need to be defined (see page on Maintenance and Refurbishment).

The present chapter essentially concerns tunnels of medium to long lengths, with medium or heavy traffic volume, located in places where prompt external emergency interventions are possible. These tunnels are operated with a specific organisation, dedicated to one tunnel or a group of tunnels, which are part of the same road network.

The page Short / Low traffic tunnels presents the specific conditions concerning short tunnels, or tunnels with very low traffic, or scattered tunnels situated in areas with low population densities.