Toronto, Ont. August 30, 1999 -- If the traffic next to you appears to be moving faster than you, do not change lanes because it may only be an illusion.
A new study, led by Dr. Don Redelmeier, director of Clinical Epidemiology for Sunnybrook and Women's College Health Sciences Centre and professor of medicine at the University of Toronto, suggests staying in your lane will get you to your destination safer and at about the same time as more aggressive driving. The study found that people over estimate the speed of vehicles in the next lane and thereby make undue lane changes.
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."
He says an understanding of the highway illusion may encourage drivers to consider some safety strategies. "People should recognize the illusion and resist small temptations to change lanes. The gains may be an illusion but the risks are always real."
Motor vehicle trauma is a common cause of death and disability. On an average day in Canada ten people step into a vehicle and do not come out alive. The causes of motor vehicle trauma usually reflect driver error rather than failures in the vehicle or roadway. "Falling prey to the roadway illusion may be one such error," says Redelmeier.
An inappropriate lane change may be associated with substantial risks. It causes drivers to straddle traffic flows and be exposed to two streams of vehicles. It creates a distinct hazard from vehicles approaching along the driver's blind spot. It also disrupts the traffic pattern for following vehicles.
The three year study was funded jointly by the University of Toronto and the Ontario Ministry of Health. The results are published in the Sept. 2, 1999 edition of the journal Nature.
Sunnybrook & Women's College Health Sciences Centre was formed by an act of the Legislature on June 26, 1998 which brought together Sunnybrook Health Sciences Centre, Women's College Hospital and the Orthopaedic and Arthritic Hospital, in partnership with the University of Toronto.
Steven de Sousa
U of T Public Affairs
Materials provided by University Of Toronto. Note: Content may be edited for style and length.
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