This was kind of brought up in another thread in "Tribute to Drivers".
I am posting this here so it is easier to find.
After searching the net, here is the answer......
When distance driven is taken into account, motorists without radar detectors actually have a higher accident rate per vehicle miles traveled. This point was first demonstrated in the Yankelovich Clancy Shulman Study in 1987. Their findings were reinforced by the results of a MORI (Market & Opinion Research International) Radar Detector Survey conducted in 2001 on behalf of the Driversí Technology Association in Great Britain.
The battle continues on surrounding the safety of radar and laser speed detectors. Some feel the detectors help prevent speeding and accidents, while others feel they are just an excuse to speed.
In a survey conducted by Yankelovich Clancy Shulman, detector users had 23 percent fewer accidents per mile traveled than nonowners, and drove almost 60,000 miles farther between accidents.
Reference to three independent studies on the use of radar detectors (Yankelovich Clancy Shulman Report 1987 in the USA, MORI Report 2001 in the UK, and ADRA Survey 2000 in Australia) have all shown that radar detector users are safer drivers, having fewer accidents per kilometre travelled, and being much more aware of their speed limit than non-users.
The ADRA, Mori Report and Yankelovich study all support the conclusion of independent fact finders - radar detector users have fewer accidents per kilometre travelled, are more aware of posted speed limits and in fact have slowed down the driving for users of radar detectors.
(1 ticket in my life....1990 in Gary Indiana...Trooper paced me 65 in 55mph zone. Had my BEL Express Radar Detector. No others, knock on wood!)