Types of tunnel monitoring and control system can range from virtually nothing to complex interactions of values, images and sounds that have to be made sense of. Once this array of information has been prioritised, the system may need to initiate actions, whether manually or automatically, with the aim of maintaining the safety of those using or working in the tunnel, guarding against any threats to security, and maintaining an optimum level of operational economy. In all of this, tunnel operations have to cope with the far from predictable behaviour of the public, fires and fumes.

Operational complexity generally increases with the number of passages included, their length, junctions, and the levels and variety of traffic. The type of traffic, such as freight vehicles, may include potential and often unknown hazards.

For all but the least trafficked tunnels an operational decision-making framework is necessary, not only for the different variations of ‘normal’ working, but all foreseeable types and locations of hazardous situations. In addition to the tunnel operator’s own staff the framework should include and be integrated with the plans of any necessary outside organisations such as fire and rescue teams, police and contractors.

During ‘normal’ operation the tunnel control system has to manage situations such as:
• night and day operation;
• other light changes due to weather variations;
• high levels of usage producing excess exhaust emissions or dust;
• extremes of temperature with possible freezing or mist creation;
• user vehicle breakdowns;
• maintenance access required to equipment and tunnel bores.

Fire has naturally dominated safety and tunnel operational design thinking in recent years. The usual causes are hot or ignited materials being brought into the tunnel on vehicles or collisions (especially with flammable loads or large fuel tanks). However, there are many other scenarios of possible emergency incidents. Non-fire incidents can include:
• vehicle collisions, possibly involving hazardous materials – permitted or illegal;
• large fuel, lubricant or chemical leakages;
• failure of the tunnel fabric or equipment;
• erratic/dangerous driving including driver health failures;
• terrorist or similar threats or malignant actions with dangerous materials involved.

Integrated control
There are many different types of monitoring devices to check and measure environmental conditions and hazardous incidents, and of course tunnel equipment has its own control systems, but relatively few companies supply complete control systems. One company that does is Siemens.

In its systems each alarm has a priority FLAG. The tunnel operating system has an alarm management protocol that works through the alarrms according to the priority flags and current incident level.

The control systems of tunnel equipment can be interlinked with automatic responses programmed in, where meaningful. However, according to Siemens, many tunnel owners and operators still prefer to initiate incident responses manually, including during an emergency. The current trend is towards semi-automatic systems that allow the tunnel operator up to one or two minutes to initiate a response, or failing that there is a preprogrammed response.

Siemens also supplies control systems to help reduce the number of traffic jams, and thus tunnel congestion and queues, with optimised traffic flow guidance. This is no small achievement since, according to the Federation of German industries, clogged roads cost over EUR1bn (USD1.2bn) a year in Germany alone, and obstructed tunnels can be a particular problem. For example, dealing with breakdowns and fires is considerably more difficult in tunnels than on open highways.

Siemens has developed a system that recognises overheated truck brakes, even before tunnel entry, so that an alarm can be sounded in the event of danger. Also, a radio–frequency identification (RFID) system registers information regarding the contents of vehicles with hazardous, or even high-fuel, loads, and relays the information to the control centre so that fire services have the appropriate extinguishing agents on hand should fire break out. Tests of the new system were due to begin in the Aubing Tunnel near Munich.

Siemens systems are also used in many other tunnels’ fire protection systems in tunnels on Zurich’s A3 western bypass and the A4 link between Zurich and central Switzerland.

P Ducker Systems (PDS) has also developed a road tunnel monitoring system fully integrating plant light, video, audio, ventilation, electrical power, pumping and traffic data together. The Matrics system can be used to test whole tunnel systems before installation, delivering a substantial reduction in project time-scale, cost and risk, and forms the basis of all tunnel systems being installed in the A3 Hindhead Tunnel in England. PDS says that Matrics co-ordinates data to enable improved situation analysis and event response, and can be configured to provide recommended response to emergency situations where action is needed based on predetermined event plans. See below for particular reference to lighting control.

Fire detection
Siemens fire protection starts with its Surveillance video smoke detection technicology with patented edge extraction process. This enables intervention forces to gather valuable information remotely on smoke characteristics and changes inside the tunnel. For more targeted fire response this is combined with the FibroLaser heat detection and locating system. This redundant fibre-optic cable can detect fire within one minute and pinpoint its locations within three metres of the ignition point. Each cable can be up to 4km long, divided into thousands of ‘individual sensors’ by dedicated electronics and software. The system is constantly tested automatically to ensure high availability.

Another cable-type multipoint heat detector, recently introduced to the market, is the SecuriSens MHD 535 from Securiton. It has been specified after tender by the Swiss federal roads office (ASTRA) for the 9.25km-long Seelisburg Tunnel on the A2 motorway, part of Switzerland’s north-south transport access. When completed in 1980 the Seelisburg was the world’s longest double- tube road tunnel and is still Switzerland’s longest. Since its opening it has undergone a steady programme of improvement works, including current preparations for a large-scale overhaul including replacement of the fire alarm system.

The SecurSens MHD535 has numerous sensors, in clearly defined positions, that signal any rise in temperature or infrared radiation. Securiton claims ultra-sensitivity and fast response and calculation times. Apart from the cable the system also includes the cable terminal signal processor and software. According to the software programming the processors determine whether to trigger a pre-alarm or a full alarm. Temperature values are transmitted to a management system via a serial interface. The system is reliable in temperatures of –55 to 125°C and 100 per cent relative humidity, and is maintenance free.

The fibre-optic linear heat detection (Distributed Temperature Sensing – DTS) system from AP Sensing has been the subject of field trials under authentic environmental conditions carried out in co- operation with the SP Technical Research Institute of Sweden (Koffmane & Hoff 2010). The trials detected test pool fires within 30-40 seconds after ignition, which is about half the time required by the German RABT standards. A trial involving wooden pallets took two minutes to detect due to slower fire development. In all cases the first alarm was initiated by rate-of-rise temperature before the actual temperature value trigger point had been reached. The sensor cable survived all tests despite high temperatures, allowing continued monitoring.

In a review of current fire detection systems for road tunnels featuring the Securiton MHD 535 cable system, Dr Arnd Rogner of Metaphysics (Rogner 2010) concluded that for the automatic detection of tunnel fires and the subsequent initiation of cost sensitive fire ventilation and fire brigade alarms, linear heat detectors are the only 100 per cent reliable detector with a minimum of faulty alarms. However, the system must be able to react to temperature gradient since a tunnel vehicle, such as a car, cannot tolerate a temperature above 50°C .

Visual analysis
It is well known that closed-circuit television (CCTV) can be important to monitor what is going on and, with recording facilities, post- incident analysis. More recent developments, such as the previously mentioned Siemens Surveillance technology, have added various facilities for live image analysis that can greatly enhance anti-intruder security processes and for identifying unusual situations automatically.

Sound Transit in Seattle has a particular problem in controlling access to the dual- transport Downtown Seattle Transit Tunnel (DSTT) with multiple possible access points with short distances. In addition to a careful analysis of the problem (Cummins 2010), Sound Transit is developing a solution to re- establish a ‘Critical Detection Point’, the lack of which is currently necessitating the stationing of a law enforcement response force to prevent any unauthorised access through a blind-spot of the normal access security officer. The solution uses CCTV and removes the human factor until the operator’s attention is drawn to a specific camera or location once a set of established parameters (including unauthorised encroachment on the light rail right of way) has been met. The solution under development includes the AISight System by BRS Labs, claimed to be the world’s only cognitive video analytic system. It will ‘learn’ the normal activity of the DSTT and recognise and alert for abnormal behaviours.

Kenneth Cummins, chief security officer of Sound Transit, has said. “This (AISight) system is different from traditional rule or algorithm-based analytic systems. The Strength is a system with less complexity and set-up criteria that results in a more adaptive, effective and accurate system reducing the impact on Link Light Rail service caused by false alarms.”

Ventilation
Correct control of tunnel ventilation fans and dampers can be one of the most difficult functions of tunnel control systems, especially in emergency situations. There have been many approaches to the correct ways of fire and smoke control through ventilation, since location, fuel and oxygen availability are all vital factors. The relatively simple task in one-way road and rail tunnels (providing escape ways are clear), can be much more complicated in some underground structures.

The maximum relevant monitor data collection is therefore vital so that tunnel users can be directed to the safest escape routes and so that fire and rescue teams can be fully informed of the situation on arrival. Large tunnels may have a round-the-clock fire and rescue team present, but in most cases the local teams are trained specially to react in critical tunnel situations in the best way in co-operation with tunnel management, including on-site training.

Expert analysis of tunnel performance at the design stages, with incidents at all feasible locations, must be carried out so that emergency action scenarios and correct actions can be determined in advance. In complex situations it is possible to programme control systems for automatic actions once the location and nature of the hazard has been determined, or human tunnel operators relied upon in simpler situations.

Specialist ventilation consulting engineers such as HBI-Haerter draw up plans for both normal ventilation requirements and airflow and smoke control during incidents, including refurbishment of existing structures with new or improved systems. In the latter cases provision must also be made for the safety of tunnel workers and users (if permitted) during temporary situations.

Ventilation can be a high proportion of tunnel energy usage. Siemens approach to keep a check on this is to calculate energy consumption on normal daily operation, and also with ‘standard’ incidents. In the case of major incidents requiring large increases in fan power, specific agreements are set up with local power providers.

The monitoring instrument range from SICK-Maihak includes mainly carbon monoxide (CO) determination and various environmental conditions that can be determined through visibility measurement through scattered light intensity. As a toxic gas, CO emissions from exhausts or low- oxygen combustion are one of the most dangerous air contaminants in tunnels. In addition to CO, the Vicotec range has models to determine smoke, nitrogen dioxide (NO2), nitrous oxide (NO) and general visibility. The Smotec450 smoke detector has a heated chamber for evaporation of droplets, and contamination control, to ensure correct measurement of smoke, It also has facilities for automatic control.

The Flowsic200 air velocity measuring device has no moving parts but determines flow direction and (optionally) air temperature over tunnel and shaft diameters up to 35m. Visibility devices are also useful in controlling traffic control, including warning of inadmissible (overheight) vehicles. One such is the Hisic450, which, due to the necessity to mount it outside the tunnel to prevent large vehicle access, is protected against extremes of weather including an optional built-in lens heater to prevent condensation and icing.

Similarly the Sigrist Photometer range of instruments is used in road and rail tunnels for early fire and smoke detection, dust concentration and general visibility through scattered light intensity measurement. In the Sigrist FireGuard the scattering angle, measuring arrange, response threshold and signal processing are optimised for smoke and fire detection. There is also a temperature sensor for localisation of the temperature incident, and an optional heater for elimination of fog. Calibration is claimed simple even in high dust concentration.

Lighting
Adjustment of lighting can be one of the most important functions of tunnel control under normal conditions. Variations of light at the portals, from nighttime to bright sunlight, must be balanced by graduated lighting into and on exiting the tunnels to allow drivers’ eyes to accommodate the change without being temporarily blinded. Lighting control can also be important for better energy consumption economy.

P Ducker Systems and Thorlux Lighting co-operate to provide what is described as ‘a reliable, energy efficient and user friendly solution for road tunnel applications.’ ‘Soft start’, digitally dimmable control equipment regulates each lamp output according to external lighting conditions. Extended maintenance periods and substantial running cost savings are offered.

Mayer’s road tunnel lighting control system complies fully with international standards published by the Commission Internationale de l’Eclairage (CIE) in order to avoid the ‘black hole’ effect on drivers using the tunnel. Its main components are a light sensor for continuous measurement of luminance of the tunnel entrance and portal, a stand-alone controller for automatic luminaire switching at the tunnel entrance, and an illuminance meter for measuring and recording light (incident lighting) with the tunnel to ensure lighting levels conform to specified parameters.

Optimal lighting, and consequently its monitoring, has been the subject of particular development in recent years, not only at the tunnel threshold but also within the tunnel to avoid driver boredom and fatigue. LEDs and electrodeless lamps are in development from which potential future tunnel lighting can be produced. In a recent poster session at ISTT Frankfurt (Buraczynski et al 2010), the authors say that the design for the ideal tunnel lighting system should include an understanding of symmetrical and asymmetrical lighting, the various light sources, the different tunnel lighting zones, current lamp and ballast technologies, etc.

Communications
Contacting tunnel users to warn them and advise them of correct actions during an incident have long been problematical, with conventional intercom systems often drowned out by noise in the tunnel. In road tunnels warnings can be transmitted via drivers’ radios, if they are switched on as usually advised.

In metro systems GSM repeaters have been installed, as in Frankfurt (Ries, 2010), to enable passengers to use mobile phones for emergency calls. The repeater system also covers staff handheld radios throughout the underground area. Fixed emergency phones have also been installed in a wide range of locations, allowing the caller to contact the control centre of the metro operator. CCTV connected to the control centre also monitors the phones. Existing public address was retained but brought together at a command post to enable emergency use by the local fire department.

Signage
Another aspect of tunnel control is signage, which is very important for controlling or stopping traffic movements, and for showing users the escape routes and equipment that might help in evacuation operations. Of course for signage to have any chance of working, it must be noticed (detection), and must be understood (identification), particularly in environments of difficult visibility such as smoke.

Work has been undertaken in measuring the visibility of notices in tunnels (Schneider & Koennecke 2010) related to size, contrast and visibility distance.


The Vicotec smoke and noxious gas detector from SICK-Maihak Testing the components of Siemens’ RFID system to identify hazardous loads Infrared image of a truck before tunnel entry showing hot spots [Siemens press photo] Actuation of ventilation dampers is an important element of ventilation for smoke control and fire oxygen starvation [Photo: HBI Haerter] Jet fans offer considerable flexibility in ventilation control [Photo: HBI Haerter] Thorlux lighting near the portal of a road tunnel with Scanlight control from P Ducker Systems Quickly noticeable and understandable signage is vital for both normal traffic control and incident management [Siemens press picture]