The railroad bridge designer is frequently involved in planning for the replacement of an existing bridge that is carrying operating tracks. The designer must know the owners tol erance for detouring trains and/or the time the track can be out of service and make these constraints part of the design-erection procedure.
Grade separation projects to take vehicular and pedestrian traffic under operated tracks requires the bridge designer to understand and utilize the owners requirements to ensure safe train operations. Railroad owners may provide their own design criteria to supersede or augment AREMA recommendations. Also, a state Department of Transportation (DOT) may use its specifications for part of the design. Designers need to understand the interests of all parties as well as their responsibility to the bridge owner. Note that the term underpass is sometimes used, denoting a structure that carries the railroad traffic over the other entity.