by municipalities of installing a fee structure
for the use of motorways, bridges or tunnels during high
use periods for the purpose of moderating traffic flow
. Congestion pricing, which is based on simple supply and demand principles
, has been used effectively in high density urban
centers such as London and Stockholm that use electronically-collected toll
systems . In the U.S. it has been limited
to high-occupancy toll roads with mixed results in reducing traffic flow on non-toll highways.