TORONTO - Every hour spent behind the wheel represents a 20-minute loss in life expectancy because of the risk of being involved in a fatal motor vehicle accident, say researchers, who calculate that even a slight reduction in speed by the average driver could save lives.
"When drivers try to speed to get to their destination faster, they actually lose more time because the savings from faster travel are offset by the increased prospect of a crash," said lead investigator Dr. Donald Redelmeier, a staff physician at Sunnybrook Health Sciences Centre in Toronto.
"The 20-minute penalty for each hour spent driving ... is completely invisible to most drivers. But it is there lurking in the background, and at the end of the year, it adds up to about 45,000 deaths." (About 3,000 people in Canada and almost 42,000 in the United States die in motor vehicle accidents each year.)
A study with co-author Dr. Ahmed Bayoumi recommends that easing back on the pedal even a bit could pay significant dividends over time.
"The estimates suggest that slowing down slightly by about three kilometres an hour would cost average drivers about three minutes daily in trip time, but save them about three hours annually in overall survival," Redelmeier said.
Applied at the population level, even a three km/h speed reduction could provide a huge benefit, he stressed. In the United States, for example, the slower speed would translate into about three million fewer crashes causing property damage, one million fewer crashes causing injury and 9,000 fewer deaths each year.
"The point here is the average driver out there isn't so far off, they are just slightly off and they are off in the direction of going slightly too fast. So it boils down to a reminder to slow down, because haste makes waste."
The study, published in Monday's issue of the Journal of Medical Decision Making, used a complex formula for estimating reduced life expectancy. It was based on a combination of computerized traffic modelling, U.S. national statistics covering driving on public roadways and the laws of physics.
The computer models took into account average distances and the time that drivers in the United States travel daily, the number of annual crashes categorized as fatal, injurious and causing property damage, as well as the expected time losses due to crashes of varying severity.
For any driver who wonders how such an estimate affects them personally, Redelmeier said the risk of a potentially deadly or injurious accident occurring exists even for the most mundane reasons for getting behind the wheel. Think of grocery shopping, a doctor's appointment or running the kids to school.
"Even on a short trip, your risk of a serious crash is a function of two factors: No. 1 is your skill and No. 2 is the skill of every other driver out there on the road with you at the time," he said. "Even a short trip can put you into contact with 100 other drivers, any one of which can ruin your life forever."
As a physician who cares for survivors of motor vehicle crashes brought to Sunnybrook's trauma ward, Redelmeier can cite some grim statistics.
"For every person who died in a motor vehicle crash, there are about 50 other people who are left permanently disabled," he said, including those with spinal cord and traumatic brain injuries or chronic pain syndromes from multiple fractures.
"We are not talking about these egregious cases of street racing ... I've been amazed at how many patients I look after in the aftermath of a crash that was due to excess speed - but not excessive, wild speeding."
Redelmeier said strategies such as photo radar, traffic-calming programs and street racing crackdowns could cut traffic deaths, as well as the number of people left with lifelong disability.
Individual drivers also need to take it slower, he said, pointing to a spate of 14 pedestrian deaths last month in the Toronto area.
"It's another example of speed. The difference between the next pedestrian fatality and no event whatsoever is usually about one or two seconds of attention. So these small differences in speeding can really make a huge result in vulnerable road users as well ... That would be another argument to slow down."