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Study: Driver Response Slower When Using Cell Phone Than When Drunk
Knight Ridder
March 23, 2002

New research sponsored by a British auto-insurance company concludes that talking on a cell phone while driving can be more dangerous than being drunk behind the wheel.

The Direct Line study, carried out over three months by the Travel Research Laboratory, involved testing the reaction times and driving performance of a panel of volunteers using a driving simulator. Researchers tested how driving was affected by talking on a hand-held phone, a hands-free phone, and when drivers had consumed enough alcohol to be above the legal drink-drive limit.

In the study, drivers' reaction times were, on average, 30 percent slower when talking on a hand-held phone compared to being drunk and nearly 50 percent slower than under normal driving conditions.

According to the tests, drivers were less able to maintain a constant speed and found it more difficult to keep a safe distance from the car in front.

Using a hand-held phone had the greatest impact on driving performance. On average it took hand-held phone users half a second longer to react than normal, and a third of a second longer to react compared to when they were drunk. At 70 mph, this half-second difference is equivalent to traveling an additional 46 feet before reacting to a hazard on the road.

Participants in the study stated that they found it easier to drive drunk than when using a cell phone (hand-held or hands-free).

In addition, drivers using either a hands-free or hand-held phone significantly missed more road warning signs than when drunk.

Direct Line commissioned the TRL research following a 2001 survey it conducted that found that four out of ten British drivers -- equivalent to around 10 million UK motorists -- admit to using a mobile phone behind the wheel.

The TRL Driving Simulator was used to provide a realistic driving task in a safe and controlled environment. Twenty healthy experienced drivers were tested in a balanced order on two separate occasions. The drivers were males and females aged 21 to 45 years. Before starting the test drive, they consumed a drink, which either contained alcohol or a similar looking and tasting placebo drink. The quantity of alcohol was determined from the participant's age and body mass using the adjusted Widmark Formula (the UK legal alcohol limit 80mg / 100ml, equivalent to the U.S. standard of .8).

The test drive had four driving conditions: on an expressway with moderate traffic; maintaining a safe distance when following another vehicle; attempting to negotiate a bend in the road; and driving on a divided highway with traffic lights.

During each condition the drivers answered a standard set of questions and conversed with the experimenter over a cell phone. The independent variables in this repeated measures study were normal driving, alcohol-impaired driving, and driving while talking on hands-free or hand-held phone.

Main Findings
Driving performance under the influence of alcohol was significantly worse than normal driving, yet significantly better than driving while using a phone. Furthermore, drivers reported that it was easier to drive drunk than to drive while using a phone.

  • Drivers who were using a hand-held cell phone reacted a half second slower than when they were driving under normal conditions. Any significant delay in reaction times increases the risk of having a crash and the crash severity.
  • Hands-free impaired driving less than using a hand-held mobile phone. However, even hands-free phones impair driving more than alcohol.
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