Traffic Tunnel

a tunnel built at the intersection of heavily traveled urban traffic arteries to allow various types of vehicles to cross the intersection at different levels (see). Special structures or sections of roadway may be provided to allow pedestrians to cross traffic arteries (seePEDESTRIAN CROSSING). The placement of traffic tunnels is coordinated with the system of urban traffic circulation, the planning of streets and construction along them, and the installation of underground cables and sewers.

A traffic tunnel usually has a two-grade profile. As a rule, such a tunnel consists of one enclosed (tunnel) section and two open (ramp) sections that provide for the flow of traffic in two directions. Three lanes in each direction are customary in the USSR.

Traffic tunnels are constructed at a shallow depth and most often in open trenches. The enclosed section of a traffic tunnel is usually made of precast reinforced concrete in the form of a closed, two-bay frame. The open (ramp) sections consist of retaining walls, reinforced-concrete foundation blocks, and a drainage chute, which are combined into a single structural system by concreting the joints. Traffic tunnels are protected against water penetration by a waterproof lining. A reinforced-concrete framework is cast along the upper parts of the ramp walls and serves as a base for a parapet. Lampposts and the supports for trolley-bus power lines are usually installed on the parapet.