Pedestrian overpasses and underpasses allow for the uninterrupted flow
of pedestrian movement separate from the vehicle traffic. However,
they should be a measure of last resort, and it is usually more appropriate
to use traffic-calming measures or install a pedestrian-activated signal
that is accessible to all pedestrians. This is also an extremely high-cost
and visually intrusive measure.
Such a facility must accommodate all persons, as required by the ADA.
More information on the specifications for accessing overpasses and underpasses
can be found in the Draft Guidelines for Accessible Public Rights of
measures include ramps or elevators. Extensive ramping will accommodate
wheelchairs and bicyclists, but results in long crossing distances and
steep slopes that discourage use.
Studies have shown that many pedestrians will not use an overpass or underpass
if they can cross at street level in about the same amount of time.8, 9 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. Grade separation is most feasible and
appropriate in extreme cases where pedestrians must cross roadways such
as freeways and high-speed, high-volume arterials.