"Road congestion" refers to heavy traffic and overcrowding on the roads, when there are too many vehicles trying to use the same space, causing delays and slower movement. Full definition
The company suggests a new «transit tax system» to fund subway repairs, that charges based on road congestion at given times, rather than on the type of travel vehicle. (ny.curbed.com)
Also road congestion pricing schemes have been implemented in a limited number of urban areas as a transportation demand management tool to try to reduce traffic congestion and air pollution. (en.wikipedia.org)
Today, plagued with swelling road congestion and rising air pollution, we tend to think of the two as increasingly incompatible. (scientificamerican.com)