WASHINGTON (Reuters) - Efforts to manipulate driving behavior by setting speed limits artificially low may have had just the opposite effect, eroding respect for speed limits, a U.S. researcher reported on Thursday.
More than a third of the people surveyed believed it was safe to drive 20 miles an hour above posted speed limits, and 43 percent thought it was safe to drive up to 10 miles an hour over, said Fred Mannering of the Department of Civil Engineering and Economics and Indiana's Purdue University.
"Once you start going down the road of posting speed limits below where they should be, then there's a general disrespect," Mannering said in a telephone interview.
Mannering said the problem started in the 1970s, when U.S. speed limits were set at 55 miles an hour to save fuel, even though interstate highways are designed for 70 mile an hour speeds.
While the lower speed limit did save fuel -- and lives -- Mannering said his research suggests it also made many drivers cynical.
"Now I think a lot of people set the speed limits saying, 'It's safe to go 45 -- let's set the speed limit at 35'," he said.
Speed traps -- when police await for speeding drivers -- help, because drivers are not motivated by safety concerns or even by having been stopped in the past. But they will slow down if they believe they may get a ticket, Mannering said.
"The study was funded by federal agencies. They wanted to see if you actually set the speed limits as they should be set, to set it on engineering judgment, would people start complying?"
Mannering believes so.
In Indiana, the speed limit on highways was recently raised from 65 to 70, Mannering said. "The speeds went up," he said -- but only by 3.2 miles an hour on average.
"That would suggest that if you are setting the speed limit close to where it should be, (the average speed of drivers) doesn't keep galloping up."
For the latest study, Mannering surveyed 988 Indiana motorists. Thirty-six percent thought it was safe to drive 20 miles per hour over the speed limit, Mannering said. Another 21 percent thought it was safe to drive up to 5 miles an hour over the speed limit.
More than 40,000 Americans are killed in motor vehicle crashes annually, according to the U.S. Centers for Disease Control and Prevention, which says motor vehicle crashes are the leading cause of death for U.S. teens.
Reporting by Maggie Fox, editing by Philip Barbara