Current practice of many agencies that operate and maintain highway tunnels is recorded, and guidelines that past experience suggests will produce generally acceptable fulfillment of motorists needs over a wide range of conditions are presented. An agencies operating policies, because they determine how much traffic delay is acceptable, what procedures are used for controlling ventillation and lighting, and how much dirt may accumulate before walls are cleaned, will determine the extent of the continuing problems and costs encountered in tunnel operation. To minimize the traffic problems associated with the restricted lateral and vertical clearances, many tunnels have some method for traffic and surveillance control. Such methods include monitoring by personnel, television or vehicle detectors, portal signals, variable message signs, and photocells to detect overheight vehicles. Hazardous cargoes are prohibited. The frequency of washing of tunnels (monthly, weekly, or semi annually) depends on traffic volumes and types, geometrics, weather and other factors. The equipment used consists of a detergent spray truck and a rinse truck. Burned-out lamps may be replaced as they occur or once a week, by special platform trucks or bucket trucks. Tunnel ventilation may be transverse, semitransverse or longitudinal and large fans are used to assure an adequate supply of fresh air. Two or more independent sources of electric power are available at most tunnels. Comments are made on personnel training. Specific features which require consideration in tunnel design include the following: lanes should be at least as wide as on approach roadways shoulders should be provided where feasible and vertical clearances should be the same as on adjacent highways; equipment should be off-the-shelf insofar as possible; and standard sign colors and messages should be used.
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