Traffic evaporation
2022-11-12 → 2026-08-08
What is traffic evaporation?#
Traffic evaporation describes the reduction in motor-vehicle trips that can follow a road closure or reallocation of road space. Some drivers use another route, but others change when, where, or how they travel or do not make the trip.
Is it real?#
A review of more than 70 cases across 11 countries found that congestion was rarely as bad as pre-project predictions (which tend to be “excessively pessimistic”): on average, 21.9% of the vehicles previously using the treated road or area (median 10.6%) could not be found anywhere in the surrounding area afterward. The traffic disappeared rather than diverting to nearby streets.
Cases#
Cheonggyecheon#
Seoul removed 5.8 kilometers of elevated highway and four of eight surface lanes to restore Cheonggyecheon. OECD’s review of before-and-after monitoring found that most of the former traffic did not reappear on adjacent streets or elsewhere in the urban area. The principal responses were shifted departure times and a significant increase in Metro use.
Pontevedra#
The city of Pontevedra saw a ~90% drop in car traffic after pedestrianizing its historic center.
Barcelona#
Nello-Deakin (2022) studies the case of Tactical urbanism in Barcelona: traffic on 11 intervention streets fell 14.8% relative to the rest of the city while immediately adjacent parallel streets gained only 0.7%, meaning most of the displaced traffic evaporated rather than diverting.