Mixed-Traffic Bridge

a bridge for the simultaneous movement of different types of traffic, for example, railroad stock and motor vehicles. Mixed-traffic bridges may have the thoroughfares located at different levels, as on a double-deck bridge, or on the same level. In the first case, it is generally necessary to build a ramp to bring the traffic down from the upper level and to move the upper-level thoroughfare away from the axis of the bridge. A motor-vehicle roadway is usually located on the upper level, since the maximum permissible grades are steeper than those for a railroad track and the minimum radius for curves is correspondingly smaller. In the second case, two motor-vehicle lanes (for two-way traffic) are often situated on either side of the railroad tracks, and it is necessary to construct overpasses. Despite the additional expenditures necessitated by ramp or overpass structures, a mixed-traffic bridge is frequently more economical than separate bridges for each type of traffic, especially in urban areas. (See alsoMUNICIPAL BRIDGE.)