Lifestyles

How speed measurement works

Lidar has always been my favourite speed measuring device.

I could target individual vehicles with accuracy and rapidly measure their speed, even on a busy highway. Radar could not do the job nearly as well as it could not be easily relied on for a specific vehicle's speed in a busy environment.

An officer starts a shift by checking the instrument to ensure that it is operating as intended by the manufacturer. An automatic power on self test must produce the expected responses.

Next, a series of known fixed distances were tested by operating the laser are receiving the correct measurements. Finally, the aim point was verified by passing the sighting dot over a distant object and listening to the change in pitch of a generated tone.

Once this was done, the instrument was ready for use.

A safe site with a good view of traffic was selected and the lidar was put to use. The aiming dot was placed on the vehicle to be measured and the trigger pulled.

A train of laser pulses was emitted, received and analyzed by the device which calculated the change in distance from the vehicle to itself over time and displayed the speed for me to see and decide whether to take enforcement action or not.

The nature of the very narrow laser beam made it precise to aim at individual vehicles. At 300 metres, a spot roughly the size of an orange was reflected from the vehicle.

As long as there was a clear line of sight between the vehicle and the liar there was no doubt about who the measured speed applied to.

For more information on this topic, visit www.drivesmartbc.ca. Questions or comments are welcome by e-mail to comments@drivesmartbc.ca. Tim Schewe is a retired RCMP constable with many years of traffic law enforcement experience. His column appears Thursdays.

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