Computer models of vehicles traveling on a congested roadway were developed to test perceptions of highway traffic speed. In the model, the next lane generally appeared to be moving faster even if all lanes had the same average speed. Videotape recordings of actual Toronto traffic were screened to driving students. These studies, also showed that people believed the next lane was going faster even if it was slower. It s an illusion, says Dr. Redelmeier.
Vehicles spread out when going fast and pack together when moving slowly.
Thus, a driver can pass many vehicles in a brief time interval whereas it takes much more time for the driver to be overtaken by the same number of vehicles. The illusion gets worse if roads are congested or drivers tailgate. Psychological factors also contribute to the traffic illusion, says Redelmeier. Drivers direct more attention ahead rather than behind, consequently, vehicles that are passed, mentally turn invisible whereas vehicles that overtake stay conspicuous. Comparison glances at the next lane are also more frequent when drivers are more idle.