Surveillance and Control Systems for Highway Tunnels

Unlike open highways, tunnels require special attention to maintain safety under normal and

abnormal traffic conditions. Most modern tunnels, including their approach roads, require a

centralized control system to meet these goals Al though not all tunnels require the same

attention or installed features, they all have the following general features. Note:

The dimensions shown in this chapter are indicative guidelines. All English unit equivalents

are soft.(rounded) conversions of metric.]

SURVEILLANCE AND CONTROL SYSTEMS

These systems provide means to

1. Monitor traffic flow and identi& impending congestion or stoppages caused by

breakdowns or accidents

2. Maintain a safe tunnel environment, responsive to traffic density and travel speed

3. Communicate travel restrictions to motorists approaching and passing through the tunnel

4. Mobilize emergency response to clear mcidcnts within the

5. Initiate, when appropriate, the necessary systems operation for emergency conditions

6. Monitor the status of tunnel service equipment to ensure continued operation and

availability when needed.

Central Control

The contml center is usually located in a tunnel ventilation or administration building and is

manned 24 hours a day. For low-volume rural tunnels or short-length tunnels that are really

extended underpasses, an alternative is part- time remote monitoring with tunnel equipment

operating automatically.

Human Control

The common control element is the need for human intervention to judge the extent and

se4verity of incidents, followed by initiation and supervision of corrective measures and

emergency response until conditions have returned to normal.

OVERVIEW OF AVAILABLE TECHNOLOGY

Tunnel Configuration

Most mad tunnels are dual-bored or immersed tubes each carrying two or three full-width

traffic lanes with an offset or minishoulder on both sides to safety barriers (see Figure 24-1).

Approach roadway shoulders are carried through short tunnels but are eliiiiinatéd or reduced

to offsets on high-construction-cost tunnels. A rule of thumb states the cost of tunnel

cónstniction will directly increase on an algorithmic scale with the tunnel diameter. Full-time

traffic monitoring has been shown to be more cost effective than providing full shoulders.

Thnnels are nornially designed for directional operation with provisions to operate btdirection

ally should the adjaceni boreltuhe be closed for emergencies maintenance. Crosspassages

between the tunnels are provided for emergency evacuation, access to fight tunnel fires, a

location to install equipment control centers, and in a number of long tunnels, vehicle

turnaround.

Tunnel Surveillance and Control

Equipment

The following traffic control devices, used to monitor vehicle flow, stop traffic, close

individual lanes and/or a binnel, and provide visual instructions to motorists passing through

the tunnel, are installed in the tunnel roadway on the walls or suspended from the ceiling.

Fig. 24-1. Typical tunnel cross section.

Vehicle detectors Loop detectors embedded in ech traffic lane with video radar/microwave detectors mounted overhead to support or replace the loop detectors are used to monitor vehicle volume, speed, and occupancy and, by processing this data, identify the probability of stoppages.

Signs and signals. Spaced at regular intervals over the roadway are 10- or 12-character variable-message sighs (VMS) with lane-use signals at both ends. The signs are spaced at regular intervals so that two units are visible ahead. Below the VMS and mounted horizontally is.a standard three-head: traffic signal. These units should be double-faced to provide a front to back display when the tunnel is operating reversed or bidirectional. This combination of sign and signals provides traffic control continuously through the tunnel (áee Figure 24-2) Alternatives to this arrangement, particularly where space is at a premium are - -

— The VMS sign centered between a dual-purpose lane-usel tiaf tic signal units - r

— Interval location of.VMS/signals/VMS/etc.

— Smaller (vertical) units at closer spacing

• TekvLcion cameras. Closed-circuit television (CCIV) cameras, either ceiling- or wall-mounted, are spaced throughout the tunnel to provide full coverage. They are coupled with the vehicle detector to provide the visual verification that an mcident has occurred.

• Emergency exits. The locations of cross--passage doàrs are marked with strobe lights mounted above or at walking level together with a flashing arrow and the word exit included on the wall side of the overhead sign and signal dispJays.

Safety and Environmental MotiltoHng

The following monitors are used to detect fires, measure air pollution levels, and sense dangerous spills in the tunnel:

• Heat detectors. Ceiling-mounted thermal- detectors or infared area -detectors provided as a backup alert in support of the CCTV system to detent a fire. See Chapter 19 for an in- depth discussion of detectors.

Fig. 24-2: Tunnel variable-message sign at cross-passageway

• Carbon monoxide monitors. Tunnel air is samplediso units such as infrared absorption analyzers can measure carbon monoxide (CO) levels. lmprovepents allow monitoring of NO1 to be coupled to CO monitoring. Readings from these sensors can be used for ventilation control (see Chapt& 20).

• Visibility monitoring. Reductions of visual range in the tunnel aie measured with a wall-mounted light transmitter and receiver that record the degree of obscurity caused by patti- des and diesel smoke. In tunnels with a high percentage of diesel-powered vehicles, ventilation is more often controlled by visibility requirements than CO.

• Air velocity monitors. Anemometers or ultrasonic transducers are mounted above the traffic stream to measure tunnel air velocity and direction of flow. This data is fed into the ventilation control system.

• Hydrocarbon monitors. Gas sensors in the tunnel drainage system detect quantities of potentially explosive and/or hazanions materials. See Chapter 23.

Voice Communication. A combination of radio and telephones is used to communicate directly with motorists through their car radios and maintain communication between tunnel and emergency response personnel within the tunnels and to units outside the tunnel. These systems and their role in fire safety are addressed in Chapter 19. They include

• Tetephone& Throughout the tunnels and ventllation buildings, there is a telephone system built around an electronic private automatic branch exchange (EPABX) for internal and external calling.

• QEJ1 boxes. Motorist and call boxes are located in the cross- passages to provide direct contact with the tunnel operator.

Facility radio. Operations and maintenance personnel use a two-way FM arid/or VHF radio system for communication between the control center, vehicles with mobile units, and personnel using handheld rransceivers.

• Miscellaneous radio. Separate radio systems and/or additional channels linked with the facility radio are provided for

police, fire department, and emergency medical response.

• AM/FM radio rebroadcast. The rebroadcast system provides continuous broadcast band reception for the motorist while passing through the tunnel. With this system the operator can interrupt commercial broadcasts to relay information directly to the motorists over their car radios.

Approach Koad Configuration

A plaza immediately in front of the tunnel portal or between the approach roads is used to transfer traffic from one roadway to the other, for bidirectional tunnel operations, to turn back oversize and hazardous materials carriers, and to provide access to the portal buildings. A typical arrangement

the plaza including the location and type of traffic control devices is shown in Figure 24-3.

Oversize Vehicles. The identification, stopping, and diverting of oversize and overheight vehicles requires a five- station layout that will extend one or mote miles before the tunnel plaza and tunnel portal. The location of these installations is centered around station No. 4, the last exit road before the tunnel. If there is a long gap from the last exit to the tunnel, the crossover plaza is then used to turn back vehicles. The linear arrangement of these installations are

1. Overheight Detector. Detection is made using an infrared light beam projected across the roadway just below clearance height (5 rn/I 2.5 It) with a transmitter on one side and a receiver on the other. When the beam is broken, a signal is sent to stations 2 and 3. The distance between stations 1 and 2 should be sufficient to trigger No. 2 flashing lights and gain driver recognition (5-sec minimum, or 135 rn [440 ft] at 100 kph [60 mph]).

2. Flashing Overheight Sign. Overheight detector signal activates two wig-wig flashing lights on a fixed panel sign that is downstream with the message, “When Flashing All Trucks Exit to Inspection Station Ahead.” The flashing time is usually set for 15 sec and may catch several trucks.

3. Inspection Station. The inspection station is configured similar to a weighting station. The No. I detector alarm alerts the station staff to be prepared to sort out the errant vehicle and direct it to the exit (see No. 4) or turn it back.

4. Last Roadway Exit. Jt is unlikely that once told to leave the roadway at the next exit the driver will continue and enter the tunnel; however, if this does happen or the driver does not stop at the inspection station, the vehicle will be detected again at the next checkpoint (No. 5).

5. Fail-Safe Overheight Detector. The fail-safe detector is similar to the first detector, but when triggered all signs and

-signals ahead leading into the tunnel are turned to stop/red, thus bringing the total traffic stream to a halt and preventing the errant truck from entering the tunneL The police or tunnel staff will then sort out the traffic jam and aporehend the violator. The linear arrangement of the above installation in urban settings may be severely truncated or replaced by an overpass structure with minimum clearance immediately before the tunnel portal.

Fig. 24-3. Tunnel portal plaza.

In urban tunnels, where detection and stopping over- height vehicles occurs in a plaza immediately before the portal, a crash curtain consisting of weighted-blocks chain suspended at clearance height acràss the detector location gives a sound/impact alert to the driver.

Hazardous Materials. Some classes of materials—explosive, toxic, and poisonous—are prohibited passage in tunnels. There are circumstances, however, where flamma

ble and other hazardous materials are allowed passage because alternative routes are long or will pass through local streets, which is considered more of a hazard. To allow for this passnge, vehicles are directed to -a -holding area as shown on Figure 24-3 and at scheduled times are escorted through the tunnel -

Approach Road Traffic Con troL The combination of fixed panel signs, variable-message signs, and traffic and lane signals is used to familiarize motorists with the sign and signal arrangements they will see in the tunnel. These control devices will be used to stop and maneuver traffic to single lanes or direct traffic to cross over to the other tunnel.

Approach rood signs and signals. The overhead signs and signals are larger than the tunnel units so as to be visible from a greater distance and attract the attention needed Normally, three sets of sign/signal units are needed to advise action ahead, initiate this action, and confirm -the travel restriction (see Figure 244). The traffic signals should be paired with the signing to replicate standard intersection arrangements.

Approach road CCIV. The outdoor cameras are fined with a remotely controlled mechanism to pan and tilt the camera and zoom the lens for area scanning and close-up viewing. A minimum of two cameras, one looking into the portal and the other looking away from the portal down the approach road, is required to supplement the series of in-tunnel cameras and view the approach road (see Figure 24-5).

TRAffIC CONTROL CONCEPTS

Modes of Operation

The tunnel arid approach roads should be equipped to make all changes in traffic operation using the sign and signal units described previously. As there is usually no time to call for police or tunnel staff to manually assist in traffic control for accidents, the control devices and their use must

10 CHARACTERS

LANE USAGE SIGN ir TFtAFFIC SIGNALS’

MESSAGES:

NO ENTRY • LEFT LANE CLOSED • CAUTiON FOG

NO PASSING — GO STOP AHEAD

STOP HERE .- STOP GO • MERGC—---->

RIGHT LANE • CAUTION ICE AHEAD • <--—MERGE

CLOSED • FLASHING OR MOVING CHEVRON

Fig. 24-4. Approach road signing..

be foolproof and easy to understand. Traffic changes fall into two major categories: scheduled changes and incident response. The former is a timed action with manual support staffing out on the approach road. Incident response is a yeaction requiring quick sign/signal response at the incident site and tunnel portal and then travel back to intercept approaching traffic to close lanes or redirect tunnel entry. Far

Fig. 24—S. ca-V camera arrangement.

incident response, the first objective is to stop entry of traffic into the tunnel. The holding point is the approaãh crossover (see Figure 24-3). Inside the tunnel there are always some

motorists trapped behind the incident, thus creating a need for dual response to deal with the stopped vehicles and to clear the traffic stream behind.

Sign/Signal Displays

The operator’s tools to orchestrate operations are packaged sign/signal displays, known as sign/signal plans, resident in his computer. The plans, using messages shown in Figure 24-4 with associated signals, can be prepared using the following operating procedures to organize the displays.

Basic Signing Plans

Five basic sign/signal plans (displays) are needed to control traffic, with several supplemental plans to modify these five basic plans. The following two-letter designations used to develop sign/signal plans are shown for a typical two-lane bidirectional tunnel port of a dual two-lane facility.

• NN—Both lanes operating in the normal mode at posted

• NC or CN—One lane open, the other closed. This plan is used for scheduled closure of one lane, left or tight, with the adjacent lane operating normally at reduced speed.

• CC—Both lanes closed. This plan is used to clear the tunnel for maintenance with the adjacent tunnel in two-way operation. Two or more steps are needed to reach the final closure state.

• NE or EN—One lane open, one closed. This plan is used for response to a minor incident in which traffic is allowed to continue flow past the incident, or the first stage of a tunnel closure to allow trapped vehicles to exit the tunnel.

• EE—Major incident plan. ‘Ibis plan, like the minor incident

plan, reacts from the incident site closing the tunnel upstream

while the lanes downstream remain open to allow traffic to

clear.

All signing/signal plans must include transition stages from an existing state to any of the other states or back to normal (NN) (see Figure 24-6).

Condition Change

Most- changes to traffic flow can be accomplished by using a two-step sequence of individual arid coordinated sigWsignal displays. The initial display should be advisory or warning (e.g., Right Lane Closed Ahead), followed by the

Fig 24.6. Response plan logic diagram.

action or restriction display (e.g., Keep Left, Right Lane Closed).

Supplemental Plans

These plans call for action by flashing command messages and then returning to the basic plan. Displays can be flashed on and off or kept in a momentary steady state to stop traffic.

Oration. This plan will alert drivers to reduce speed and set in line the next plan. The plan can be used as an automatic alert with incident detection to want motorists and give the operator time to follow with the appropriate action

Speed Change. Reduction in speed on the approach roadways as a result of fog, ice, or snow.

Flow ControL Driving through a tunnel is a traumatic experience for many motorists, causing overcaution andlor a complete disorientation, and resulting in the need for signing plans to stabilize traffic flow. A common occurrence in subaqueous tunnels is the loss of speed on the downgrade caused by overreaction to brake lights. This is followed by a loss of orientation and failure to accelerate on the upgrade, resulting in a sluggish crawl that greatly reduces throughput of the tunnel. This condition can only be broken up by platooning traffic to break the inertia or, in this case, lack of inertia. Plaboning is accomplished by stopping entry at the tunnel portal much like a signalized intersection; When released, traffic will flow freely through the tunnel until it reaches the end of the crawl. Traffic should again be stopped one or more times until smooth flow exists throughout the tunnel length.

Stopping time should be limited to a maximum of 3 nun, which is about the extent of motorists’ patience. The tunnel signs (Figure 24-2) should also• include messages such as “Maintain XX kph” or “Upgrade, Accelerate.”

Stop. This command is used to momentarily halt traffic approaching the tunnel to allow the turn back of restricted vehicles or escort of vehicles through the tunnel, or as the initial stage in estabJishing bidirectional flow in the other tunnel.

Action/Advisory. Action message include “Turn on Radio,”“Evacuate the Thnnel,”“Stay in Lane,” etc.

Normal Operation

Most urban tunnels have more traffic lanes on the approaches than in the tunnel; thus, the demand exceeds the tunnel madway capacity. After entering the tunnel, traffic becomes unstable and slow, which further reduces the flow. The dividing line betw&n free flow and unstable flow can be related to traffic density. As traffic density increases to the optimal flow rate (veh/hour), free flow exists. Beyond this point, as the density increases, flow and speed decrease (see Figure 24-7). A means of gauging these traffic changes is the monitoring of lane occupancy by providing occupancy readouts per lane in the control center. A green display for a traffic density of 0—20% indicates uncongestedt flow, a yellow of 20—30% indicates unstable or impeding congestion, and red for over 30% indicates congestion. Once notified of unstable flow, the operator has the following options or combinations of options to use:

Traffic monitoring. Flow control or reducing the number of

approach lanes.

Motorist advisoiy Flash tunnel signs to read “Maintain XX kph,” or prompt the motorist to regain free flow over the radio rebroadcast

Fig. 24-7. Traffic now diagram.

Incident Response

The first alert of a possible incident will be received from the lane sensing of a disruption in flow (breakdown or acci— dent). (See Figure 24-8.) The alert will automatically switch the console CCTV monitors to display the incident site. After examining the situation, the operator can verify the in— cident or reject the alami as a false alarm. Should the opera— tor not respond or delay his response, the sign/signal program will be triggereth initiating the Caution Plan and a prompt waiting for further instructions from the operator. The usual sequence after verification is for the operator to select the appropriate response plan. As the display changes are sent to the field devices, the feedback status is compared with the phange command to verify proper execution. While calling up the sign/signal plans the operator will take the following steps:

• Emergency response. Alert the emergency response crew to the location and extent -of the inéldent. Select the access mutes -to reach the site eitherby counter flow in the incident tunnel or through the adjacent tunnel and cross-passages.

• Radio broadcast. Flash tunnel signs to read ‘Turn on Radio” and then begin broadcasting instructions.

Off-site assistance. Notify-police, fire, and medical assistance with routing instructions to reach the incident site.

• Equipment operation. Change and activate tunnel service equipment—set -ventilation mode/levels, pressurize water mains, open drainage holding tasks, -stan standby power generator.

• Response supervision. Maintain overall control of response activities using CCTV, phones, and radio.

• Nonnalize. After incidcnt clearance, return traffic control devices and tunnel equipment to normal operating mode.

Tunnel Evacuation

Some accidents may require evacuation actions prompted by sign displays, radio instruction, and tunnel staff which direct motorists to leave their vehicles and exit the tunnel through cross-passage or portal. In a fire emergency, evacu

Fig. 24-8. Incident management diagram.

of stranded motorists is critical. Tunnel fires are usually identified by CCTV when viewing incidents; however, traffic queues can block the view or secondary incidents in the queue may result in a fire, which establishes the need for backup detectors. Operator action is essential as motorists may attempt to fight the fire with portable extinguishers available from tunnel niches or in vehicles. They usually will not flee the area until there is a flare-up and smoke. When smoke buildup occurs, quick, forceful instructions for direction to flee should be issued using -the rebroadcast radio, strobe lights, and signs at the cross-passages to prompt this action.

flELD HARDWARE

Detectors

The efficiency of incident detection -depends on the reliability of the vehicle sensing unit. Present practice employs

detector loops cut into the approach road and tunnel pavement. Standard traffic controllers like the 170 with programmable logic and communication medium can be used with several detector amplifiers to collect and process traffic data. Since most tunnels prohibit lane changing in the tunnel, the sensing of a stoppage can be accomplished in seconds using developed algorithms such as the queuing and flow-discontinuity programs commonly known as the California algorithm. With a 180-rn (400-ft) spacing of detector loops in each lane, the traffic controller will poll the loop amplifier at 1/60-sec intervals to summate 1-sec measurements of lane occupancy over the loop. This data is then processed locally or at the control center to develop 1-mm avenges of lane occupancy that are updated every 20 sec and fed into the algorithm. The sensitivity parameter built into the program will usually be set to accept a high (2:1) false alarm rate in order to generate quick alarms. This detection procedure is very successful when the -traffic flow exceeds 400-600 vph per lane. Detection is uncertain during periods of low volume and at night when lane changing enforcement is improbable, or it can occur when a vehicle pulls off onto a partial shoulder offset. A second algorithm based on vehicle accounting can be used to warn the operator when there appears to be a stalled vehicle somewhere in the tunnel.

Freeway traffic management systems are now using video! radar/microwave detectors to measure flow as a means to identify congestion and incidents. These units could furnish the vehicle speed input to the algorithm and eliminate the need for dual occupancy loops. However, until tested and proven in tunnel use, detector loops are recommended for queuing and counting detection.

Television Cameras - -

It is important that the tunnel be fully covered by the CCTV system to provide clear images to the operator. The tunnel cameras are fixed-focus and -mounted on the ceiling

or high on the sidewall to view approaching traffic. Positioning cameras to face oncoming traffic prevents trucks, buses, etc., blocking the camera sight lines. It is possible to add remotely controlled pan and tilt mechanisms to provide double camera coverage of an incident site, but this requires higher tunnel headroom.

Solid State Cameras. The cameras are compact charged- couple devices (CCD) fitted with 12.5-mm (0.5-in.) lenses. They are free from image lag, blurring of images. blooming, image burn, and damage from direct light. Although each camera with a fixed focal lens can cover more than a 300-rn (990-fl) length of tunnel, the cross section restraint I knits the effective range to 200 m (660 ft). Horizontal or vertical changes in alignment may reduce this range significantly, possibly to 75 m (250 ft).

Camera Spacing. A practical method for spacing the cameras in the tunnel begins with a camera looking in at the exit portal, then going back against the flow locate a camera at 200 m (660 ft) spacing (see Figure 24-5). Followiu this layout, it is possible to plot the camera sight lines on the tunnel plan and profile to see if full coverage is available. If not, cameras are added and spaced at less than 660 ft (200 m) to obtain full coverage. It should be noted the camera vision cone will not produce wall-to-wall, pavement-to-ceiling coverage immediately in front of the camera, and thus a 25 m (80 ft) sight overlap between cameras is needed.

When selecting the remaining components of the CCTV system, a balance and assurance of quality is needed. The camera should have high resolutioji and b housed in a weatherproof case. Fiber optic or coaxial cables should be used to transmit the video signals directly back to the control center. Solid state monitors with high screen resolution are standard for control room display. Since the CCTV sys tem is so important to operations, its configuration should use quality components and be simple, easily maintained, and free from unneeded fixtures such as transmission multiplexing, split-screen monitors, etc.

Outdoor Cameras. The outdoor cameras should be fitted with a remotely controlled motorized zoom lens (1:10 or 1:16) enclosed in a weatherproof case with window washeriwiper. The camera is mounted on a pan (350°) and tilt (90°) unit. Two outdoor cameras are recommended at each portal. One is located over the exit roadway to view the immediate portal area and normally is set looking into the tunnel to complete the tunnel coverage. The second camera is mounted high on the portal and will view the approach roads.

Additional approach road cameras may be needed if the surveillance length is extensive or road alignment and terrain obstructs the view. The camera height above the roadway also determines the distance viewing is effective;

increasing height increases depth of view.

Traffic and lane Signals

The traffic and lane signals each have separate use. They are mounted separately and not mixed together, so as to

avoid conflict in meaning. The traffic signals are used to stop traffic and should have 200-mm (8-in.) diameter lenses using standard three-signal heads with fiber optic light source. The outdoor signals are similar, but should have 300-mm (12-in.) lenses. The lane signal is used for lane control and is mounted over the centerline of each lane using a 300-rum (12-in.) fiber optic light point for green arrows, yellow slanted down arrows, and red crosses.

Approach Road and Tunnel Signing

Directional Signing. Directional signing should be avoided if possible at the tunnel entrance, within the tunnel, and just outside the tunnel exil However, in many urban facilities and where there are entrance and exit roads in the tunnel, this signing is necessary. Logic shows that the outdoor signing standards are not suitable nor really necessary in a tunnel. With the tunnel confinement, it is difficult to see more than 75—150 m (250—500 ft) ahead, and therefore the signing panel and lettersize can be greatly reduced. A second consideration is that the motorist has little time to read and comprehend lengthy texts; therefore, the message must be concise. Using standard 300-mm (12-in.) letter heights for two lines of text arranged to read left to right will result in a compact 900-mm (36-in.) height sign pane (see Figure 24-9). If there are several such signs in the tunnel, the ceilr ing height can be set to accommodate 900-mm (36-in:) signs. If there are only a few, all or a portion of the sign height may be fitted into a ceiling notch. If this type of signing is used extensively within the tunnel, similar arrIngements with larger lettersshould be used on the approach road to familiarize the motorist.

Regulatory Signing. Regulatory signing is used on the approach roads and in the tunnels to support the traffic and lane signals. For example, they are used to warn (“Left Lane Closed”), to impose restrictions (“Stay in Lane”), to provide motorist advice (“Turn on Radio”), or to command action (“Evacuate Tunnel”). There are several types of variable- message signing units (blank-out, rotating drum, fiber optic, or LED matrix). The matrix type can provide almost limitless numbers of messages and has the capacity to illuminate the letters/symbol points, which is preferred for use in tunnels and approach roads (see Figure 24-10).

Fig. 24.9. Directional signing panels.

Fig. 24-10. Matrix variable-message signs.

Overheight Vehicle. The infrared beam transmitter and receiver may be mounted on an overhead sign bridge, bridge abutment/pier, or on their own poles. To eliminate false alarms caused by vehicle aerials or birds flying through the beam, a minimum break time is needed to trigger an alarm. The beam can also be coupled with detector loops to prove the presence of a vehicle. For bidirectional roadways where it is not possible to erect poles between opposing travel lanes, two sets of beams are needed with a breaking logic to. determine the direction of the vehicle.

Fire Detection and Equipment

The frillowing discussion of fife detection and equipment

relates primarily to surveillance and control aspects. For a

discussion of the fire protection aspects, see Chapters 19,

20, and 23.

The first line of fire and smoke detection should be the CCTV system, but standard detectors are needed to provide backup and to identify hidden fires. Heat detectors should be. used throäghout the length of the tunnel, subdivided into alarm zones. The detectors, high-wall- or ceiling-mounted, can be individual point detectors set at a temperature level and rate of rise, linear therrno cables, or infrared area scanners.

Smoke Detection. Alarms can be generated by the visibility monitors when levels fall below set levels. These uniti are effective for small fires, which can generate large and dangerous quantities of smoke. To provide effective sensing, the number of monitors and their spacing should be increased.

Fire Extinguishers. Small fires can be easily controlled with powder or foam extinguishers, which most motorists know how to use. Extinguishers should be located in tunnel niches at each entrance door. A control center alarm should be activated when the extinguisher is removed from its

holdet

Air Quality Monitors Carbon Monoxide Monitors.

The most effective car-

boa monoxide (CO) monitor in terms of reliability, ability to

produce accurate measurements, and need/ease of maintenance and calibration is the pumped sample infrared absorption type. Each unit is equipped to handle six to eight sampling ports. The ideal location for the analyzer unit is at each portal, with sampling ports some 15—30 m (50—100 ft) inside the tunnel on both tunnel walls. This arrangement will provide dqal measurements in each tunnel, and the short sample tube lengths will enable minimum time readings. Other similar installations should be at the mid-tunnel and/or quarter point locations.

Visibility Monitors The visibility monitor consists of a light transmitter and receiver, usually mounted on the tunnel walls, to measure the smoke/particle content of the tunnel. The measurement of obscurity is directly related to the degree of visibility in the tunnel, and when concentrations reach set values fresh air is supplied to dilute this concentration. These units should be located in similar positions to the CO monitors, where the expected concentration is highest and where dual readings can be obtained for comparison.

Air Velocity Monitors. The measurement of air movement in the tunnel—velocity and direction—is needed for control and/or measurement of the ventilation system efficiency. This is accomplished by installing, inside each portal of both tunnels, ultrasonic transducers on the walls to point a signal at approximately 3.65 m (12 ft) above the roadway angled across the roadway at 45° to the receiver on the opposite wall. The analyzer unit can be housed together with the CO and visibility units.

Communication Equipment

The rebroadcast systçm contains an outdoor receiving antenna, broadband amplifiers for the standard AM and FM bands (530—1620 kllz and 88—108 mHz), a radiating tunnel antenna, and an operator switching/microphone/VHS cassette recorder.

Two-Way Radio. This system will be used by tunnel staff in vehicles or with handhe]d transceivers for communication between individuals. It is coordinated by the control center

operator. A dedicated VHF channel must be obtained for this two-way FM communication system. Local police, fire, and medical assistance may also be included in the system.

Telephone. A direct dialing telephone system for communications within the portal building, between cross- passages, and externally is provided by the EPAUX.

Motorist Call Boxes. The motorist call boxes provide direct communication with the contcol center operator, who can organize assistance as required. The call boxes should be installed at each cross-passage and on pedestals on the immediate approach road. They should be hands-free speaker- microphones with a call button. The operator will receive an alarm tone coded to indicate the location of the call box and

will then activate the unit.

Cellular Telep hone. Provision should be included in the tunnel for the installation of a 800-MHz cellular telephone system. There is an increasing use of mobile telephones to alert tunnel operators of conditions in the tunneL

l!4uipment Locations

The layout of the tunnel services can best be accomplished by using a modular arrangement or spacing to unify power feeds, remote terminal units, and maintenance areas in the cross-passage. Using a 100-m (300-ft) spacing, equipment can be installed cross-passage. This matrix arrangement shown in Table 24-1 illustrates modular spacing and preferred mounting locations in the tunnel cross section.

CONTROL (DENThR

The contml center is designed for the man—machine interface requirements, for without the need for human intervention, the computers could happily mu alone in a dark room. Much of the tunnel operation can run automatically using programmed schedules based on the time of day and limiting levels for changes. It is only when there is an abnormality that the Operator is needed.

The control center is therefore configured to first provide displays of operating status for all equipment and then providé means to change operation status (see Figure 24-1 1).

There may be some need for manual controls and hard- wired connections to field equipment, but the basic configuratiou and communication to remove equipment is deetronic code and computer-aided.

Status Displays

Means should be available to status of monitor all display devices, sensing monitors, and operating equipment, but not

Table 24-1. Tunnel Control Ariangement

Fig. 24-11. Control ceuten

all at one time or even continuously. The priority level of status addressing should be arranged in the followitig order.

First Priority. Traffic incidents or major equipment events that require urgent operator response include

• Traffic accidents

• Firefsmoke detection

• Power failure

• Dangerous levels of CC)

• Hydrocarbon spillage

• High water levels in sumps

Second Priority. This level includes condition alerts such as detection of a possible inciident, equipment failure. or communication shutdown. These alanns require operator acknowledgment and are then recorded. The computer simplifies recordkeepiOg both by one-line printout of a hardcopy (paper) record and by logging in computer file storage.

Third Priority. Every change in traffic control and

equipment operation is logged for record purposes.

Control Procedures

Three means of control should be -available to the operator and tunnel stalL

Computer ControL The primary control system allows the operator to send commands to the computer using the keyboard or a mouse and computer graphics to call up preprogrammed traffic management plans, ventilation plans, etc. These plans will be conflict-proof and can be run concurrently with each other, but not layered.

Manual ControL Using the computer terminal, manual switches, or both, the operator can make individual changes to any device or piece of equipment. Changes made manually may not be conflict-proof and may change again with the introduction of a command using preprogrammed plans. Manual control is usually used for testing and maintenance.

Local Con froL At the remote location of the device or piece of equipment, control is accomplished by using its local intelligent or manual control (PC or switches). Changes can be made here in the event of a communication failure from the control center or for testing and maintenance.

Map Display Panel

This floor-to-ceiling display is arranged in a semicircle to provide a panoramic view of the status displays to the operator. Centered in the panel are three large color video terminals to display computer graphic text, macro/micro line diagrams of device/equipment configurations, and their operating status. The central or primary screen will usually show a mmimap of the tunnel and approach roads with the current traffic control plan in place. The two flanking screens are used for backup and concurrent status call-up as pages from the status menu. Running just above or below are the TV monitors arranged in direction to traffic flow (top right to left, bottom left to right). If there is room to spare on each end of the panel, it is used as a special enunciating display.

CCTV Monitory. For short tunnels with a few CCIV cameras, the display panel will contain one monitor for each camera. With a larger number of tunnel cameras, monitor sequencing is recommended with 3—10 tunnel cameras coupled to each monitor in the map display panel. The sequence should not be a rotation on individual monitors but a rolling sequence through the tunnel. For example, with a 3:1 ratio of cameras to monitors, 1/3 of the tunnel would be displayed moving through the tunnel. In this way a continuous section of the tunnel can be shown. Two separate monitors, one on each end of the panel, are for the portal approach road cameras. The first sequencing monitor can also be dedicated to the second outdoor camera.

Incident Viewing. Upon alert of an incident the tunnel section display can be centered on the incident site to show conditions upstream and downstream. The operator can pull down to the console monitor the camera showing the incident and return the panel monitors to tunnel sequencing.

Control Console

The operator’s position will enable the viewing of the entire map display panel, two master video display units

(VDUs) for CCTV displays, and computer dialogue, each built into the console. Arranged around this operating position are switching panels and radio/telephone handsets. The console is U-shaped to provide desk working areas.

Annunciating or Switching Panel

The type or need for annunciating or switching panels depends on code or operating practice particular to the location of the tunnel. A fire annunciating panel may be required here and at the tunnel portals to conform with local regulations. The panel may also contain secondary or backup manual switches for some or all of the tunnel equipment.

Supen4sor or Dispatch Desk

A second controllsupervisorfcominunication desk can be located in the control center or at a secondary or remote location. The use of computer control and digital communication allows this operating freedom. For large facilities with one or more tunnels, bridges, toll, or maintenance facilities to manage, the communication needs will require this second desk. With dual VDUs, switching, and communication devices, this subcenter can provide parallel and backup control with the prime center subject to operations protocol.

Computers and Peripherals

The system is built around two industrial-grade minicomputers or PCs to provide 100% redundancy (see Figure

• 24-12). Each computer (CPU) is sized and equipped with dual disk drives, clocks, a watchdog unit, and a cotnmunicalions unit, so that individually each CPU can support all operationlalertfrecording requirements. Both CPUs are supplied with operating programs, but they are not expected to perform parallel processing. The operating software is configured to

allow the backup to assume command by simply polling status of displays and operating levels. Included in the computer room is a program desk with a terminal and keyboard to be used for testing and maintenance. This station, as with all computer input terminals, should be tied

Fig. 24-12. Cennal control layout.

into access passwords to protect access and use of the computer systems.

Communication Network

The most expensive element of the control system is the communication network. Cost and limitations of a hard-wired system have led to the use of single cable for multiplexing data transmission. flpical single cables of twisted-pair, coaxial and/or fiber optic are now used with time-division (1DM) and/or frequency-division (FDM) multiplexing.

Advances in the use of programmable controllers (PECs) has also relieved the data processing load in the control center CPUs and the volume of data interchanged between field units and the control center. This concept of distributed intelligence with multiplexing transmissions is the basis of a supervisory control and data acquisition (SCADA) system (see Figure 24-13).

SCADA Configuration

The communication system is made reliable by usingtwo techniques. The first technique is distributed processing, which involves the spreading of control processing throughout she network to minimize the severity of a single failure. Coupled with this is network redundancy. If the primary route of communication has failed, then communication s transferred to a secondary route- In simple tenns, the control center is usually in a state of waiting, receivingdevice and equipment status reports from remote terminal units (RTIJs). When called into action, they send execution commands to the RTUs and then verify that the proper change has been carried out. The RTUs control. the various downline 4evices and equipment, which include

FIg. 24-13. Network.

1. Traffic detectors sending data back to the control center

2. Traffic control equipment on hold waiting for commands, which send basic status to the control center to confirm availability

Distributed Intelligence

The control center will have the capability to interrupt and when necessary take over the duties of any downline R1’U using reserve capacity built into the communications network. Depending on the size and number of RTUs, there may be a need for two levels of downline data processing. An example of this would be a local master RTU controlling severalsubsystems that have RTUs at each piece of equipment. One or more of these master RTUs would feed information and receive commands fron the control center, and supervise the RTIJs to create a self-contained operating unit. These master RTIJs can assume command in the event of a communications break from control center.

Cable Network

The communication cable network should be configured on a semi- or, preferably, fully duplex loop to transmit and receive data simultaneously. Should a break occur within the loop, it will automatically switch to semiduplex operation. The use of independent communication loops can allow the grouping of devices and equipment having similar priority and need for high-speed transmission rate and data refreshment Other pieces may only need periodic contact at slow speeds and can be grouped on separate cabling loops. Codes of practice may also require separate cabling as for fire detection or alarms.

Software

Recent developments of computer control for industrial applications have made real-time multitasking systems available in several software packages that can be used for the general-purpose software. By using these general application packages, the amount of purpose-written software is reduced and made easier to prepare. The tunnel system package loaded into the central computers and downline in the programmable controllers should meet the following requirements.

Input/Output (110). Measurements from field monitors and change commands form this link. This data is usually translated to digital code. The 1/0 processing speed of this data is critical and must be optimized to handle the number of I/Os to be scanned while maintaining an acceptable level of responsiveness.

Man—Machine Interface (MMI). The preferred interface is computer graphics with simulated network, control panels. and logic diagrams for visual displays. Data may be input via keyboard commands, although using a mouse or trackball to manipulate a graphical user interface is more common. Programmed sequencing of group commands is essential for critical action, particularly when a trained operator

is not available. Using these devices, the operator should be able to window in quickly for status, operating, or diagnostic plans that give an overview or point display of all systems. Sound alarms including voice simulation are gaining use for MMI and are recommended.

Operating Plans and Algorithms. Within the software will be routines ranging from complex data manipulation at the central computer to relay-ladder-logic at the PLCs. These operating plans and modifications of parameter are resident in the system’s operating plans.

Database. The organization setup is housed here to assign locations, sequencing, alarms, timing, and reporting for all functional subroutines. Included are historical backgrounds of actual operating experience for input into the operating plan.

Communications Network. The SCADA network should conform to an industry standard for a local area network (LAN).

t’urpose-Wxitten Software

Title headings for tasks to be included in the application

software are

• Monitoring. Incident detection, CO levels, visibility, heat and smoke detection, sump water levels, power and equipment failures

• Man-machine interface. Computer gtaphics, alarm priority

• Operating plans. Traffic control, emergency response management, ventilation control, plant management

• Security. Entry surveillance, computer usage, watchdog, emergency power, system shutdown

• Recordkeepihg. Event logs, operating timing, traffic and ventilation histograms

• Maintenance. Operating logs, servicing alarms

• Training. Operation simulation

SYSTEM SEIJECUON

There are concerns for cost cutting and the question of whether certain features are really necessary. The basic system requirements for a short tunnel in the country and an urban high-volume tunnel are very much the same: attention to tunnel user needs. An answer to the cost question is non- quantifiable, but how well a tunnel performs is its most visible feature. Since there is such a large investment in building a tunnel, why compromise with its operational capabilities?

Basic Requirements

The basic components that should be included in the surveilmance and control system are

Traffic service. A full-time means toidentify stopped or disabled vehicles in the tunnel, their verification, and availability of on-call emergency response

• Fire service. A proven means to identify or detect fire or smoke, and the means to fight fires and evacuate trapped motorists in the tunnel

• Environment. Continual monitoring of levels of tunnel pollution and a means to dilute excessive amounts

• Lighting. Full-time tunnel illumination with battery backup to prevent total darkness

Flooding. A drainage system including sumps. pumps, and

outfalls/storage -

• Power. Dual sources of power supply or a built-ia standby diesel electric power unit

DESIGN AN!) IMPLEMENTATION

System design employs engineering techniques from traffic engineering, computer/communication design, and software development. To produce a successful end product, their combined input is required from design inception to final acceptance testing and hand over to a client.

Traditional Design

Thete are two basic design and contracting methods used to implement the system—the traditional preparation of design plans and specifications for contractor construction, or the

system manager approach. For the former, the designer prepares either a materials/installation specification or a per

-formance specification for typical contract bidding to furnish/install or design/purchase/install. This method can be successful only by contracting directly with prequalified control system contractors. When this specialty work -is lost within a large tunnel civil contract, it is difficult to stop this element from being slighted by the prime contractor and viewed as a nuisance to be passd piecemeal to subcontractors. Success is seldom certain.

System Manager

The system manager is -a selected firm working under an engineering service contract to design, prepare procuremeat and installation contracts, and be responsible for system integration, documentation, and training. Underthis method there is freedom to make changes as the system is being developed without the responsibility of claims for extras. The system manager provides the application software, which is the key element-in a successful operating system. -

The complete services package associated with a control system should include the following:

Operating manuaL The design and installation reflect specific operating procedures to define goals that should be spelled out in this manuaL This document should be flrstorganized in the system inception stage and then refmed -and updated throughout the design and installation process.

- Maintenance manuaL This is an organized reference of original designs, shop drawings, manufacturers’ pedifrcations, and maintenance procedures with parts listed for all hardware

items. The software manual should include descriptions of source programs and programming instructions for diagnostics and parameter changing.

Training. Formal book and classroom training may familiarize staff with the system, but the opportunity for hands-on involvement with the contractor/system manager during installation, testing, and commissions is far superior.

Initial operatioa Provisions to supply a management staff during start-up for a specified period to further train the takeover staff, debug the software, and apply corrective inaintenánce is a sound investment It also gives greater assurance that the warranty/guarantee response will be prompt and complete.

Warranty/guarantee. This provision ensures responsibility for a specified period for all components including nnnufacturer product in-house warranties that may have expired

OPERATION AND MAINTENANCE

There are two types of tunnel facilities: tunnels with tolling and those without. The former tend to become kingdoms unto themselves, while the later will contain essential staff and equipment and thus better illustrate the basic needs for operating and maintaining a tunnel.

Organization

The tunnel organization is made up of day staff working a regular 8-hour day, 5 days a week, and shift workers assigned to the day shift from 6 A.M. to 2 P.M., a night shift- from 2P.M. to 10 P.M. or the graveyard shift from 10 P.M. to 6 A.M., on a ‘7 days a week operation. The number of employees needed to man the shifts will be 40% more than the actual number to cover a 7-day week, holidays, vacations, etc. The thy staff perform routine administrative and maintenance tasks. The shift workers monitor traffic, inspect and perform routine maintenance, and are on call for êmergencies. During the graveyard shift, most of the major maintenance work is carried out. The permanent tunnel staff supervise temporary or contracted laborers and specialists.

Permanent Key Staff

The permanent key staff is divided into three divisions having the following duties (see Table 24-2):

Management.

• Tunnel manager Provides overall facility management, maintains dealings with government agencies, the community and contracted services.

• Supervisors. One supervisor is assigned to each of the three shifts to supervise the day-to-day operation and management of the tunnel, working staff, and contracted services. Assumes command for emergency response.

• Administration. An administrator, secretary, and clerk handle correspondence, budget, finances, and purchasing.

Table 24-2. Permanent Key Staff

Operations.

• Control center operators. The center is manned continually with an operator who monitors traffic and equipment operation. The shift supervisor provides his relief

• Response crew. This crew is manned by two members on both the day and night shift and one for the graveyard shift. They are the manual arm for the control center operator to man the emergency response wreckers, check prohibited vehicles, assist motorists, enforce traffic control, and keep the roadways clear.

Maintenance.

• Technical specialists. This four-member crew, three on day shift and one on graveyard shift, perform routine inspection and equipment maintenance and supervise contracted services work. Included in this crew are technical specialists in mechanical, electrical, and electronic equipment.

• Maintenance crew. Included with the shift workers is a labor force to assist the technical specialists to perform general janitorial, cleanup, painting, patching, replacement, and repair work. This crew can be permanent staff, part-time drawn from a larger Highway Department, or included in contracted services (i.e., janitorial, tunnel washing).

Contracted Services. Many large transportation authorities serving a number of facilities including tunnels have their own workshops, staff, and equipment to be almost 100% self-maintaining. However, for most individual tunnels it has been found beneficial to contract out all maintenance work except for the day-to-day caittaking. Included below are the professional and technical services suitable for on-call and off-site service:

• ProfessionaL L.egal, labor relation, employment service, engineering, facility inspection, accounting

• Site maintenance. Structural repairs, paving, lighting, lamp replacing, signing, pavement marking, painting, tunnel washing, janitorial

• Equipment repair Fan motors, pumps switchgear, electronic equipment

• Equipment servicing. Computers, radios, telephones, data transmission, office equipment

Tolling Facilities. There are few tunnel facilities where tolls are not needed: no tolls, no tunnel. For tunnel operation, a toll plaza is a godsend where oversize or hazardous

cargo vehicles are easily dealt with. It provides a built-in traffic crossover or turn—back area and can be the excuse for traffic delays.

Toll Plaza Layout. The usual transition and number of toil booths in the plaza are three booths per throughroadway traffic lane arranged with a truck lane(s). The booth should be arranged to gap automatic collection with manual collecdon. There is a strong move to introduce automatic vehicle identification (AVI) for toll collection.

Plaza Locaáon. The tolling facility may be located immediately in front of the tunnel portal to consolidate tunnel operations and tolling.

• Toll supervisor Stationed in the support building (administration or toll building) with an overview of the plaza operation; the supervisor maintains supervision of toll plaza operations.

• Toll collectors. Shift workers in the collection booths to handle manual and truck booths. A plaza supervisor is included to oversee operations and provide relief.

• Revenue security. The collection of manual and automatic collection bàoths revenue is bandied by this group together with the assembly of change packages and the accounEing of return packages. Coin and token counting is also handled by this group.