Considerations for Overpasses and Underpasses

A woman jogs up a ramp toward a pedestrian overpass in San Luis Obispo, Calif.Pedestrian over- or underpasses (tunnels or bridges) are only helpful for busy pedestrian crossings across wide, high speed, or extremely high volume streets where there is no other safe way to get pedestrians across the street. While over- and underpasses can work well to keep pedestrians safe from busy or high speed vehicle traffic, they are also very expensive and obtrusive. Additionally, underpasses may involve significant crime, drainage, lighting, and maintenance concerns. Overpasses will result in better security, but will result in complaints from nearby homeowners about the loss of privacy and aesthetics. Also, in some locations, pedestrians will not use the over- or underpass if they believe they can save time by dashing across the street. This puts them in greater jeopardy.

Since ramps for overpasses (and underpasses) must be gradual enough to accommodate wheelchair users (with a maximum slope of 8.33 percent), they can be very lengthy and can greatly increase the distance traveled to cross the street.

A tunnel enables students to walk under the road in Boone, N.C.These ramps require a considerable amount of space on both sides of the bridge, which adds to the cost. The construction of underpasses can be very disruptive to traffic for a significant amount of time. Pedestrian underpasses or bridges can cost$1 million or significantly more. Accordingly, over- or underpasses should usually be constructed as a last resort. Overpasses work best when the topography allows for a structure without ramps (e.g., overpass over a sunken freeway). Underpasses work best when designed to feel open and accessible.

More information about overpasses and underpasses can be found in the Facility Design section.