Electrical power supply

Most of the tunnel equipment and systems require electrical energy to operate. Therefore, equipment for supplying power to the tunnel must be installed. This installation has to satisfy two essential requirements:

• Supply safe and sufficient power to allow all the equipment to operate
• Meet the needs under all operational situations (normal, degraded, critical, emergency).

The power required for supplying a tunnel is directly related to the nature and number of equipment installed in it. Depending on the amount of electrical energy required (kWh), power may be supplied in low voltage or high voltage (Fig. 1).

Each country has its own regulatory requirements with regard to tunnels and a specific structure in terms of distribution networks: therefore, the architectures retained may be significantly different in tunnels with similar characteristics. However, some identical principles can be noted, such as:

• The presence of a standby power supply (redundant supply, diesel generator, etc.),
• The installation of a device that can compensate for a total loss of power supply. This system (uninterruptible power supply (UPS), diesel generator., etc.) supplies electricity to equipment critical for safety, during a limited period of time.

Tunnel lighting system

In the majority of tunnels, the natural penetration of light does not allow satisfactory visibility for users. It is therefore necessary to install artificial lighting to improve visibility conditions and comfort.

In terms of functionalities, the lighting installation must allow for:

• normal lighting that provides appropriate visibility for users, both day and night
• safety lighting that provides minimum visibility for users, to enable them to leave the tunnel in their vehicles in case of power outage.
• evacuation lighting, such as evacuation marker lights, to guide tunnel users on foot in the event of an emergency.

Normal artificial lighting usually includes two successive zones:

• an entrance zone (also called a reinforcement zone) where the lighting level is reinforced at the tunnel entrance and gradually decreases further along the tunnel
• an interior zone that corresponds to the rest of the tunnel. In this area the lighting level is constant and much lower than in the entrance zone.

In some tunnels, where there is a risk of glare at the exit, there is an exit reinforcement zone.

Entrance lighting

Motorists approaching a tunnel entrance will often experience what is known as the “black hole effect”. This is because luminance levels inside the tunnel are much lower than those outside and our eyes have difficulty adapting to the sudden difference. To alleviate this effect, a higher, “reinforced” level of lighting must therefore be provided at the tunnel entrance. This will ensure that drivers can see objects within the correct stopping distance before entering the tunnel. It will also help to prevent them from slowing down, which is important to maintain optimal traffic flow.

The amount of light required to avoid the black hole effect will depend on the bness outside the tunnel (sunny or cloudy weather). Luminance measurements at portals are normally used to determine and adjust the lighting levels required for the entrance zone.

In order to enable drivers’ eyes to adapt from the entrance zone lighting to the interior zone lighting, the entrance lighting level is gradually reduced as drivers move along the tunnel.

Interior zone lighting

Once drivers have adapted to the lower luminance levels in the tunnel, sufficient lighting is needed in the interior zone for safe passage. Luminaires in the interior zone are therefore spaced at regular intervals, throughout the rest of the tunnel. Daytime and night-time levels of interior zone lighting are controlled by a photoelectric cell.

The design of a lighting installation should respect several criteria, notably those relating to the:

• level of luminosity and lighting on the pavement
• level of luminosity and lighting on the side walls
• uniformity values for the different operating regimes
• glare values.

Several types of installations are possible; the most common are symmetrical lighting and counter-beam lighting.

Symetrical lighting

In symmetrical lighting systems, light is distributed symmetrically with respect to a plane perpendicular to the axis of the tunnel. An equal amount of light is sent towards each end of the tunnel. This system is generally used in the interior zone. It may be used in the entrance zone for tunnels which have a slow approach speed or where there is not enough room to install lighting fixtures above the carriageway.

Counterbeam lighting

Counterbeam systems project light in the direction of motorists, in conditions that avoid dazzling. This type of system, which should be fitted above the carriageway and facing the traffic flow, uses the photometric properties of the pavement (bness and specularity). It is suitable for use in entrance zones if there is sufficient room to install light fixtures above the carriageway. It has advantages in terms of investment costs and operation costs, especially when the approach speed is relatively high (>70 km/h).

In addition to the type of lighting system, attention should also be paid to coatings on the side walls of tunnels which can affect the overall efficiency of the chosen system. For symmetrical lighting, wall coatings should preferable be light coloured.  In the case of counterbeam systems, darker, but more specular coatings are preferred. 

Depending on the characteristics of the tunnel and the type of lighting system, the light fittings may be installed in one or more rows, above the road or at the top of the side walls.

Tunnel ventilation system

The term « ventilation » combines several functions: pollution ventilation, smoke extraction, and sometimes ventilation for environmental protection purposes.

As explained on the page "Ventilation principles", in certain cases, ventilation in road tunnels can be achieved without the need of mechanical equipment (natural ventilation). However, in most of the tunnels with a length above some hundred meters, mechanical ventilation is unavoidable, which requires the design of a tunnel ventilation system (see the page on "Design and dimensioning").

The characteristics of the ventilation equipment to be installed strongly depend on the type of ventilation system for normal operation and fire scenarios.

Longitudinal ventilation systems utilize the tunnel tube as the “duct”. With the help of an air-jet placed in the tunnel air column, the flow resistance can be overcome by converting the jet momentum into static pressure.

The air jets can be placed at the tunnel entrance (Saccardo), blowing outside air into the tunnel or as ducted fans (usually called jetfans) along the tunnel, each one accelerating part of the tunnel air flow. Jetfans can work in both tunnel directions. (see section IV.2 “Longitudinal ventilation” of the PIARC report 1996 05.02 “Road Tunnels: Emissions, Environment, Ventilation”).

When a fan is installed into a tunnel a considerable decrease in the thrust occurs when the unit is close to the soffit or wall of the tunnel or in a niche. In those cases, it is recommended to use additional devices in order to maximize the installation factor. Examples are deflectors, inclined metal sheets, inclined silencers or nozzles. Section 4.4.4 "Ventilation" of the PIARC report 2017 R02 "Road Tunnel Operations: first steps towards a sustainable approach" provides some examples of efficiency improvement in longitudinal ventilation.

In some countries, air filtration systems have been put in place to mitigate the impact of vehicle emissions on ambient. Section 4.4.5 "Air cleaning" of the PIARC report 2017 R02 "Road Tunnel Operations: first steps towards a sustainable approach" provides some examples and approaches in different countries.

Jetfans operating in a tunnel can generate high noise levels, and can have adverse effects on speech transmission between people in the tunnel. This may become a safety issue when the noise level prevents the tunnel users from understanding what they are asked to do or when it makes it difficult for the firemen to communicate with each other. Therefore, some care must be taken in the assessment of sound emission by the jetfans.

Transverse ventilation uses ducts that run parallel to the tunnel. Two kinds of ducts are typically utilised:

• Fresh air ducts are used to inject fresh air into the tunnel in order to dilute the polluted gases produced by the vehicles;
• Extraction or exhaust ducts are used to remove vitiated air or smoke and hot gases produced by the fire from the tunnel volume. In some cases, the extraction capacity may be used in order to limit the longitudinal velocity in the tunnel under normal operation.

Extraction for smoke control is usually concentrated to a zone smaller than the length of the duct by the addition of motorized, remotely controlled dampers, also known as “point extraction”. The fans serving the ducts are often located in ventilation plants close to the tunnel portals or shafts; however, many variations can exist.

The extraction fans must be sized to ensure the required extraction airflow rates for all fire locations in the tunnel. In the past, extract ducts were typically connected to the tunnel with a number of small, evenly spaced open vents. This concept has since evolved by replacing the small, open vents with larger vents equipped with remotely controlled motorised dampers and spaced further apart. The use of thermal fuses and panels has been assessed and found to have adverse effects: the effectiveness of the smoke control system using such thermal devices was found to be compromised by the untimely opening of some dampers and/or the opening of dampers in non-optimal locations.

The thermal resistance of the fans must ensure that the extraction of the hot smoke is possible with any configuration. Cables, junction boxes and all other non-protected parts of the ventilation system should have the same fire resistance as fans. For more details on fire resistance of other equipment, see section VII.5 "Fire resistance of equipment" of the 1999 PIARC report 05.05.B "Fire and Smoke Control in Road Tunnels". Additional information on maximum temperatures measured during the Memorial Tunnel and the Zwenberg Tunnel fire tests can also be found in this PIARC report 1999 05.05.

To fulfil their function, dampers must be able to withstand normal tunnel environmental conditions and to operate under emergency conditions.

Ventilation equipment should meet a number of specifications, including resistance to fire and acoustic performance. Chapter 4 "Ventilation" of Report 2006 05.16 and its appendices 12.3 "Jet Fan calculation procedure", 12.4. "Smoke dampers" and 12.6. "Sound impact of jet-fans" provide additional information on ventilation equipment for longitudinal and transverse systems.

Life cycle aspects need also to be accounted for in the design and selection of tunnel ventilation equipment. Additional information can be found in the PIARC report 2012 R14 "Life Cycle aspects of electrical road tunnel equipment".

In some cases, as for complex or urban tunnels, specific considerations need to be considered in the equipment requirements, as described in chapter 7 "Other equipment & operating facilities" of the PIARC report 2016 R19 "Road Tunnels: complex underground road networks".   

Ventilation tests

Because the ventilation system plays a major role in tunnel safety, it is essential that it operates properly and effectively at all times. To achieve this goal, sets of tests have to be defined and adapted to specific tunnel specifications The primary objective of road tunnel ventilation system testing is twofold:

• to verify the functionality of all elements of the system, both at the time of ordering (factory and acceptance testing) and in-situ (functionality testing at specified intervals);
• to verify the in-situ performance of the system and its component parts by comparing it to the design specifications.

Three kinds of tests are usually performed in order to check the equipment and the safety objectives of the ventilation system:

• Reception (factory) tests: are aimed at checking that the equipment actual performance matches the specified requirements. The test guidelines generally point out the procedures for these test operations.
• On-site unit tests: are aimed at checking that equipment operation is in accordance with the project specifications.
• Integration tests: are aimed at checking that the safety objectives match, especially with regard to smoke control. The first set of integration tests may be performed without a fire in order to quantify the ventilation capacity, and a second set of tests may involve a calibrated fire in order to account for the buoyancy effects and to visualize the smoke development.

It is generally impossible to perform integration tests with fires as large as the design fires. Most commonly, the main purpose of these tests is to train tunnel operators and members of the fire brigade.

The list of tests and corresponding timetables must be adapted to each particular tunnel, and depends on the installed equipment, traffic volume and degree of utilisation of the installations, and cover several aspects, including:

• Visual Controls
• Electrical Measurements
• Airflow Measurements, Fan Pressure
• Airflow Measurements in Ventilation Exhausts
• Airflow Measurements at Smoke Dampers
• Noise Measurements: at air intakes and ventilation equipment outlets in order to determine the condition and aging of the silencers and the fans and in the machinery rooms to verify protection of workers.
• Shelters and ancillary rooms ventilation
• Fire Trials

Chapter 8 "Operational responsibilities for emergencies" of the PIARC report 2007 05.16 "Systems and equipment for fire and smoke control" describes in more detail the appropriate ventilation tests for ventilation systems.

Supervisory Control And Data Acquisition systems (SCADA)

In a road tunnel, the equipment plays a vital role for the safety of users. The operator therefore has to monitor such equipment continuously to determine its status (operational or faulty) and/or its operating mode (automatic, manual or stopped).

Many devices are servo-controlled by sensors and operate automatically (e.g.lighting, ventilation.) according to pre-determined thresholds. Others are activated or deactivated depending on the operating conditions. It is thus useful for the operator to be able to remotely control them (such as signals, variable message signs, barriers, ventilation as fig. 1, lighting, pumps ...).

As the equipment may be operated very differently (continuously, occasionally, or very rarely), it is necessary for the operator to have information on the operational duration (hour used) of each item.

 

Surveillance, control-command and data archiving are very often performed by a single system: the Supervisory Control And Data Acquisition system (SCADA): see Fig.2

Several SCADA systems are available worldwide and their performance is being improved constantly. The systems installed in road tunnels of comparable characteristics are therefore rarely completely identical, even for the tunnels belonging to the same operator. Even so, the architectures follow certain rules that are widely prevalent:

• Collection of information via loop networks
• Intelligence (programmable logic control notably) installed near the equipment
• Separation of networks: acquisition, transport and supervision
• Redundancy of certain sub-assemblies to improve their dependability.

With the development of internet and connected devices, SCADA are becoming increasingly vulnerable to cyber attacks. As they are the core of the safety process, efforts must be made to  protecting them from this new threat.