Bicycle Safety Guide and Countermeasure Selection System
Example of shared-use path between two highway bridges. http://www.pedbikeimages.org/ - Margaret Gibbs
Barriers to movement such as rivers, freeways, canyons, and railways may present severe impediments to bicyclist travel. 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 minimizes hazards to bicyclists. Bridges should also be well-lit. The traffic volumes and speed, as well as bridge length, will all help determine the appropriate accommodation for bicyclists. In locations where bicyclists are expected to ride in the travel lane, a shared-lane marking may be appropriate. It is important to also consider the future growth to the area as bridges are built to last over 50 years.
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). 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 a buffer of two feet 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) recommends a railing height of at least 42 inches.
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.
Bridges and overpasses built for all modes of travel provide continuity of access for bicyclists and prevent significant detours for bicyclists due to unsurpassable natural or built barriers.
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 million for adding a cantilevered shared path to an existing bridge.
Bicycle and pedestrian overpasses are generally very expensive, though some cost savings can be realized depending on the materials used. Cost information is typically provided as a lump sum cost, but can also be presented as a cost per square foot.
Overpasses (not included in table below) have a range from $150 to $250 per square foot or $1,073,000 to $5,366,000 per complete installation, depending on site conditions.
The cost for specific types of bridges can vary substantially, based on the specific situation, materials, and other factors, as demonstrated in the table above for wooden and pre-fab steel bridges.
Authors and Acknowledgements