Electrical installations for vehicular traffic tunnels

The safe passage of traffic through road tunnels requires 24-hour per day availability of the many electrically based systems provided in these tunnels. These systems have to operate under hostile environmental conditions, with limited opportunities for maintenance because of the paramount need to keep traffic flowing. For capital cost reasons they have to be designed and installed without, if possible, increasing the minimum geometric dimensions of the tunnel established to allow passage of the designed traffic. The author argues that safe passage of traffic may be said to be attained if the systems provided ensure that the flow of traffic can pass through the tunnel with about the same speed, degree of safety and comfort as is present along the adjacent stretches of road. Traffic flow can be safe and smooth only when sufficient visual information is available concerning the `run of the road´ and the presence (or absence) of obstacles, including vehicles and their movements