Barriers to movement such as rivers, freeways, canyons and railways may present severe impediments to bicyclist travel. According to the Institute of Traffic Engineers’ Innovative Bicycle Treatments², the City of Eugene, OR, determined through a users’ survey that bicycle and pedestrian bridges were needed every 1.6 to 2.4 km (1 to 1.5 mi) to cross a geographic barrier through town – in this case the Willamette River. Bridges built to accommodate all modes of travel are typically preferable since they connect with the existing street network. If separated bicyclist/pedestrian facilities are provided, security issues must be addressed. Bridges must be properly designed to provide safe, accessible approaches, with sufficient space for bicyclists to navigate ascents and descents as well as across the overpass, and safe riding surfaces that take into consideration expansion grate design and seam placement that minimize hazards to bicyclists. Bridges should also be well-lit.

If retrofit measures are needed for existing structures, space on the bridge may be provided on the street, on walkways if they are wide enough to safely accommodate pedestrians and bicyclists, or even on a separate deck as was done on the Steel Bridge in Portland (see case study #2). If sidewalk access is provided, ramps should provide bicyclists direct access from the street. Sidewalk access may be desirable if traffic volumes and speeds are high, the bridge is long, and there is insufficient roadway space (outside lanes or shoulders are narrow) to safely accommodate bicyclists.

When bicyclist space is provided near bridge railings or near motorized traffic, extra horizontal width or buffer of 0.6 m (2 ft) or more is recommended to protect bicyclists in the event of a crash or wind blast, especially on higher speed bridges or high spans where wind gusts may be strong. Railings should also be provided. The American Association of State Highway and Transportation Officials (AASHTO)³ recommends a railing height of at least 1.4 m (4.5 ft).

Access from adjoining streets should be as direct as possible to reduce out-of-the-way detours for bicyclists, and designs should endeavor to minimize conflict points at entrances and exits.