Pedestrian and Bicycle Bridges and Tunnels

Pedestrian and bicycle bridges can range from short connections over streams to extensive structures over freeways and major highways.

This underpass in Boulder, CO provides students with a route to school that does not require crossing a busy street.

Pedestrian and bicycle bridges and tunnels are sometimes appropriate to improve street or route connectivity or provide routes over or under roadways. Overpasses and underpasses are most appropriate when children would otherwise be forced to cross freeways or major multi-lane, high-speed arterial streets to travel safely to or from school. There are also situations where pedestrian signals are not warranted and/or feasible and overpasses and underpasses may be useful during these times. Such separated crossings are most feasible where terrain conditions allow for crossing over or under the roadway without having to provide long ramps or steps. ADA guidelines require that all facilities be accessible to all users, including those in wheelchairs and the visually impaired. Pedestrian bridges and tunnels can be very costly to build. Bridges over an arterial street will likely cost more than $1,500,000 and will often require extensive ramps. The high cost of such grade separation should be considered along with security issues, drainage problems, lighting needs and maintenance.

Pedestrian and bicycle bridges and tunnels can range from short connections over streams to long bridges with extensive approach ramps over highways. The location selected for any bridge or tunnel is an important factor in its effectiveness. Like all pedestrian crossings, any facility that is inconvenient or requires an indirect path will simply not be used. The effectiveness of a grade-separated crossing depends on its perceived ease of use by the users. Pedestrians will weigh the perceived safety benefit of using the bridge versus the extra effort and time it will require when making a decision about where to cross. Often it is best to redesign the crossing or modify the traffic control at the at-grade crossing instead of building an over- or underpass. Some schools assign adult school crossing guards at nearby bridges to assure that students use them.

Treatment: Pedestrian and Bicycle Bridges and Underpasses


Pedestrian and bicycle bridges and underpasses separate pedestrians and bicyclists from vehicular traffic and allow for safe, uninterrupted pedestrian and bicycle traffic flow. They are most appropriate for crossing a freeway or other high-speed, high-volume arterial street or rail-line.

Expected Effectiveness

The effectiveness depends largely on the likelihood that they will be used by pedestrians and bicyclists as an alternative to at-grade crossings. For bridges and underpasses that are used by a large proportion of pedestrians and bicyclists, studies have found that pedestrian-related crashes decreased by 91 percent.[24] However, other studies have determined that if the walking time to use an overpass is 50 percent longer than crossing the street at-grade, then the bridge or underpass will not be used and will be ineffective in reducing crashes.[25]


Costs range from $500,000 to $4 million, depending on required right-of-way acquisition and site characteristics (NCHRP Report 500, Volume 10, 2004).

Keys to Success

  • Bridges are best suited in areas where the topography allows for a structure without ramps.
  • Underpasses work best when they can be designed to feel open, well-lit, and safe.
  • Both bridges and underpasses should be accessible to all pedestrians, including those in wheelchairs.

Key Factors to Consider

  • Bridges and underpasses will not be used if a more direct route is available.
  • These structures need to be located to minimize the travel required to access them. Fencing may be needed to channel pedestrians and bicyclists to the bridge or underpass.
  • It may be difficult to obtain funds and meet ADA guidelines for ramps that require extensive right-of-way.
  • Crime, vandalism, graffiti, lighting, and drainage issues may also cause problems.

Evaluation Measures

  • Number or percent of pedestrian and bicycle crashes and changes in probability of being involved in a crash once treatment is in use.