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Other speed detection devices - speeding camera

Our article about Speed Cameras discusses concerns that have been raised about the reliability of those devices in the Australian Capital Territory. Speed cameras are not the only way that police decide a driver is speeding. Other methods of detecting speeding violations also create the possibility that an innocent driver will receive a mistaken violation notice.

Radar units are generally mounted on the outside of police vehicles.

A digital readout is mounted on the inside. Radar units are typically pointed at vehicles ahead of the police vehicle. The radar units used in the ACT are “down the road” units, meaning they cannot be pointed to the side. While it is possible to point a radar unit at vehicles behind the police vehicle, it is difficult for the officer to know which vehicle a radar is detecting if the officer must make that observation in a rearview mirror.

When the police vehicle is in motion, the computer can only calculate the speed of another vehicle if it knows the speed at which the police vehicle is traveling. The accuracy of police vehicle speedometers is therefore critical to the accuracy of speed readings provided by a radar unit.

Laser units are used to detect speed by pointing the laser at a vehicle and activating the device.

It takes less than half a second for the police to get a speed reading after pointing a laser unit at a vehicle and pulling the trigger. Laser units generally operate more quickly than radar.

While “moving radar” units can be used while a police vehicle is in motion, a laser unit can only be used when it is stationary. If you spot a police vehicle parked on the side of the road, an officer may be operating a laser unit. By the time you see the officer, however, the officer has had a chance to see you and may be able to obtain a laser reading before you have time to slow down.


The simplest way for an officer to determine a speeding violation is to “pace” a speeding vehicle by following it in the officer’s vehicle for a period of time while maintaining an exact distance. The officer then notes the speed shown on the police vehicle’s speedometer. The speedometers of police vehicles are periodically certified as accurate, although it is always possible that the certification of any particular vehicle was neglected.


A laser or radar unit is only as good as its operator. On a busy street or highway, whether the officer “tagged” the right vehicle with the laser or radar is often in question. All units have a limited range and readings obtained from a vehicle beyond that range, or from a vehicle that is too close, may not be accurate. In some cases, careful questioning of the officer can reveal that the officer failed to follow, or does not understand, the correct procedures for operating the unit and for verifying the accuracy of readings.

Radar generally bounces off the largest reflective surface in the area. Whether that happens to be a particular car or a larger truck, or even a metallic sign or a power station, is not always easy for an officer to determine. In some cases, infraction notices based on radar readings can be challenged on that basis. That is particularly true when photographs demonstrate that the radar would need to pass through power lines, traffic signs, or other metallic objects that could affect the radar signal before reaching traffic.

The use of speedometers to justify infraction notices for speeding is the simplest case for a lawyer to defend. The speedometer is recording the speed of the officer’s vehicle, not the vehicle the officer is pacing. If the officer was not maintaining an exact distance but was, in fact, driving faster than the car the officer was following, the basis for the speeding accusation can be undermined. Skillful questioning of the officer may induce the officer to admit that possibility.

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