Staring at the road can interfere with drivers' ability to pass safely, says research study

December 23, 2000

Overtaking and passing other cars is considered one of the more dangerous situations facing drivers. New research based on driving simulations suggests that staring at the road while driving at a high-speed may put drivers at greater risk for rear-end collisions when they attempt to overtake and pass another car. These findings are reported in the December issue of the American Psychological Association's (APA) Journal of Experimental Psychology: Human Perception and Performance.

Focusing on the road in front of your car for too long can be hazardous say psychologist and lead author Rob Gray, Ph.D., of Nissan Cambridge Basic Research and co-author psychologist David Regan, Ph.D., of York University. "Motion adaptation - which is a change in the motion-detecting cells in your brain produced by prolonged viewing of moving objects - can occur when driving on a straight empty road. This can have detrimental effects on visually guided motor actions such as overtaking another car and can lead to a fatal error."

"It is not uncommon during highway driving that we are exposed to the type of repetitive motion that can produce motion adaptation," said Dr. Gray. "For example, when driving straight ahead on an empty highway, a driver's visual image continuously expands and objects such as the road markings and trees continually move past our eyes. As the driver continues to drive and gets closer to the trees, the image of the trees keep getting bigger and bigger. The trees actually move from the center of the driver's windshield towards the edge of the windshield until they disappear out of view. When we look at something that always moves in the same way it causes the motion-detecting cells in our brain to adapt to that motion," explains Dr. Gray.

In our study, we examined the effects of motion adaptation -produced by driving on a virtual highway - on overtaking maneuvers in a driving simulator. Eighteen 19 to 36 year old experienced drivers participated, said Dr. Gray. The driving simulator consisted of the frontal two-thirds of a Nissan 240SX convertible and a wide-field-of-view (60 degrees horizontal X 40 degrees vertical) display of a simulated driving scene. It provided realistic feedback through the torque in the steering wheel and audio feedback consisting of engine noise that increased with faster car speeds, according to the study.

Following five minutes of driving on a straight empty highway, drivers initiated overtaking of other vehicles substantially later (by 0.2-0.5 seconds) than comparable maneuvers made following five minutes of driving on a winding country road, said the authors. "This delay in the initiation of overtaking appears to be caused by an overestimation of the time to collision with the lead vehicle (i.e. the driver has the illusion that she/he has more time before a collision will occur) caused by motion adaptation. To make matters worse, we also found that motion adaptation caused our participants to drive considerably faster (by 5 mph on average)."

These changes in driving behavior resulting from motion adaptation substantially reduce the margin for error and place the driver at a much higher risk for a rear-end collision, said Dr. Gray. If a driver delays the initiation of overtaking, it increases the chance that they will clip the rear corner of a car when trying to pass. Motion adaptation it also dangerous because it occurs without the driver being aware that it is happening. Drivers in our experiments did not know that they were driving faster and initiating overtaking later.

Motion adaptation can also cause problems when a driver exits a highway and enters an off-ramp, said Dr. Gray. The increase in driving speed resulting from motion adaptation can cause drivers to lose control when going around a sharply curved off-ramp. Unequally spaced white stripes painted across the road leading up to an off-ramp have been used to create an illusion that counteracts motion adaptation and reduces driving speed.

This intervention has been reported to reduce the number of accidents and is now commonly used on roundabouts and off-ramps. However, it does not solve the problems associated with overtaking and passing. "We are currently exploring strategies for reducing the build-up of these dangerous aftereffects during driving. For example, dashboard displays which elicit eye movements and prevent the driver from staring straight ahead," said the authors.
Article: "Risky Driving Behavior: A Consequence of Motion Adaptation for Visually Guided Motor Action," Rob Gray, Ph.D., Nissan Cambridge Basic Research and David Regan, Ph.D., York University; Journal of Experimental Psychology: Human Perception and Performance, Vol. 26, No. 6.

(Full text of the article is available from the APA Public Affairs Office or at )

Rob Gray, Ph.D., can be reached by telephone at 617-374-9670 or by email at

The American Psychological Association (APA), in Washington, DC, is the largest scientific and professional organization representing psychology in the United States and is the world's largest association of psychologists. APA's membership includes more than 159,000 researchers, educators, clinicians, consultants and students. Through its divisions in 53 subfields of psychology and affiliations with 59 state, territorial and Canadian provincial associations, APA works to advance psychology as a science, as a profession and as a means of promoting human welfare.

American Psychological Association

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