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.
- Provide continuity of access for bicyclists.
- Prevent significant detours for bicyclists due to unsurpassable natural or built barriers.
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- Width of travel lanes and existing walkways, length and height of span, and motor vehicle travel speeds and volume, should all be considered when determining the best place to provide space for bicyclists.
- Extra buffers may be needed for "shy distance" from railings or from traffic to protect bicyclists from sudden wind blasts or gusts.
- Bicyclist access on multi-modal bridges should be provided since these bridges connect with the existing street network. Separate facilities may be desirable to prevent long detours for bicyclists (if additional multi-modal bridges are infeasible) or to connect multi-use paths or separate corridors.
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Varies widely, depending on whether a new bridge is constructed or a retrofit of existing installation is provided. The type of facilities and changes implemented also affect cost.
For retrofit treatments, Portland examples include from $20,000 for restriping to add bike lanes on an existing deck cross section to $10,000,000 for adding a cantilevered shared path to an existing bridge.
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