How fast do you drive?
When it comes to speeding, many American motorists don’t worry about safety. They just worry about getting caught.

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Those are the findings by researchers from Purdue University who surveyed nearly 1,000 motorists about speed limits and driving habits. They found that many drivers are cynical about the safety benefits of driving within speed limits, and many think they can drive safely while speeding as long as they won’t get caught, according to the report in Transportation Research Part F: Traffic Psychology and Behaviour.

“So the faster you think you can go before getting a ticket, the more likely you are to think safety’s not compromised at higher speeds,” said Fred Mannering, a professor of civil engineering at Purdue, in a press release. “For whatever reason, respect for speed limits seems to have deteriorated.”

Dr. Mannering used a series of mathematical equations to calculate the probability of speeding, based on data from a survey of 988 motorists in Tippecanoe County, Ind. The survey findings were consistent with other research that has shown two-thirds of all drivers regularly exceed posted speed limits, and roughly one-third report driving at least 10 m.p.h. faster than most other vehicles.

The latest research asked participants: “At what point do you feel speeding becomes a threat to the personal safety of you and your family?” The motorists were given three choices: 5 m.p.h., 10 m.p.h. or 20 m.p.h. over the speed limit.

The survey was taken before and after a 2004 media campaign launched in the county stressing the dangers of speeding that included radio and newspaper messages.

More than a third of the drivers in the survey thought it was safe to drive 20 m.p.h. over the speed limit. Overall, the vast majority of respondents said they thought it was safe to speed, with 79 percent saying it was safe to exceed the limit by 10 m.p.h. or more.

The research showed the media campaign relating to the dangers of speeding had no statistically significant impact on drivers’ views on speeding and safety. For most drivers, a “safe” speed is typically just beyond the point where they believe they are at risk for getting a ticket. That means that motorists who believe they won’t get a ticket until they go 10 m.p.h. above the speed limit are 27 percent more likely to drive up to 20 m.p.h. above the speed limit.

Notably, getting stopped for speeding didn’t seem to have an effect on whether or not a person speeds again. Both men and women drivers who had been stopped for speeding in the last year were 25 percent more likely to believe that it is safe to drive up to 20 m.p.h. faster than the speed limit, compared to those who hadn’t been ticketed.

“This is probably because people who habitually speed are not significantly deterred by being stopped for speeding,” Dr. Mannering said. “They might become slightly more conservative, but it doesn’t slow them down to the level of people who are inherently more conservative.”

To learn more about Dr. Manning’s research, read “Yes, Accidents Happen. But Why?,” published in The Times last year.

* Stuart Isett for The New York Times; November 10, 2008