How mobile Laser Traps operate
Police Laser Guns work by firing a pulsed beam of light at a vehicle which
then measures the time taken for it to return, this can take as little
as a third of a second. The beam is very narrow, this allows the enforcement
officer to be very precise in which vehicle they want to target. From
a motorway bridge any vehicle in a line of traffic could be targeted.
The beam fired from the gun is of a conical shape, the further away from
the gun, the wider the beam. This causes great problems when fitting a
Laser Detector to a vehicle, as complete coverage is very difficult to
achieve at short range, with only one sensor.
How the enforcement officer chooses which vehicles
Even though the police have all the high tech equipment for measuring
and recording the speed of motorists, it is down to the officer using
the equipment to choose which vehicle to target. A lot of people believe
that the police are checking every vehicle as they go by, this is not
the case. Guidelines state that an officer can only measure the speed
of a vehicle that they beleive to be exceeding the posted limit. This
is often why a driver with a Laser detector fitted may see a gun or van
nearby, but will not get a warning alarm as they drive by. The majority
of the time they are targeting the number plate of the vehicle as this
is normally vertical to the road, but any part of the vehicle could be
This highlights the difficulties of short range detection. The beam
is very narrow and with a single sensor it is not possible to cover
At long range it is not possible to choose which part of the vehicle
they want to target. On some Laser Guns the sight is bigger than
the vehicle. Wherever the detector is fitted it is possible to trigger
Following a vehicle being targeted
At short range it is difficult to detect, but if the vehicle in
front is targeted from long to medium range it is possible to detect
as long as the sensor is fitted the front windscreen.
When the vehicle is targeted from the rear, the laser signal will
pass thorough the rear windowscreen and trigger the laser detector
as long as no obstructions are in the way.