Speed camera traps don't always cut accidents, says a survey in Britain.
Data shows that collisions increased at a number of locations after the introduction of cameras.
In one area, the number of accidents actually went up at 17 of its 89 speed camera sites.
Seven of the 44 speed trap sites in the Thames Valley - an area which follows the River Thames from Oxfordshire in the west to London in the east - saw a hike in the number of collisions, while four of the 47 locations north of the city also saw an increase in accidents.
The statistics were revealed after Britain's Department for Transport called on local authorities to publish accident and casualty rates for camera sites before and after the introduction of speed cameras.