Barrier Effect
The barrier effect (also called severance) refers to delays, discomfort and lack of access
that vehicle traffic imposes on nonmotorized modes (pedestrians and cyclists). The barrier
effect is equivalent to traffic congestion costs (most traffic congestion cost estimates
exclude impacts on nonmotorized travel). In addition to travel delays, vehicle traffic
imposes crash risk and pollution on nonmotorized travelers. The barrier effect reflects a
degradation of the nonmotorized travel environment. This imposes indirect costs by
reducing non-drivers’ accessibility, which tends to be inequitable, and forces people to shift
from nonmotorized to motorized travel, which increases various external costs. Studies
described earlier indicate that many people would like to walk and bicycle more but are
constrained, in part, by heavy roadway traffic.
Swedish and the Danish roadway investment evaluation models incorporate methods for
quantifying barrier effects on specific lengths of roadway (Litman 2009). Both involve two
steps. First, a barrier factor is calculated based on traffic volumes, average speed, share of
trucks, number of pedestrian crossings, and length of roadway under study. Second,
demand for crossing is calculated (assuming no barrier existed) based on residential,
commercial, recreation, and municipal destinations within walking and bicycling distance.
Estimated Benefits: Scandinavian and Canadian estimates indicate that the barrier effect
averages 0.5¢ to 1.5¢ per vehicle mile under urban conditions.