6.5 Other Speed Measuring Systems

• Library: Defense of Serious Traffic Cases in Virginia (Virginia CLE) (2020 Ed.)

6.5 OTHER SPEED MEASURING SYSTEMS

6.501 In General. Except for pacing and microwave radar, most speed-measuring systems use a form of distance/time (clocking) to compute speed. Distance equals Speed multiplied by Time and:

Speed = Distance / Time

6.502 Pacing (Patrol Vehicle Speedometer). Pacing involves following a target vehicle at a constant range; the longer the officer follows a target, the better the chance of an accurate measurement. This method depends on the ability of the officer to maintain patrol car speed, a constant distance between the patrol car and the target matching the target vehicle's speed, and the accuracy of the patrol car speedometer. The speedometer works by measuring drive shaft rotation by either digital or analog means; accuracy is good to about " 1 mph. Accuracy may be compromised if tire pressure changes or different size tires or wheels are used or the rear axle load is different from installed...