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Speed Guns

New speed detectors catch traffic violators in the act with more accuracy and less work for officers.

September 01, 2005  |  by - Also by this author

Radar guns and their laser counterparts are the bane of speeders’ existence. Some motorists even pay hundreds of dollars on radar detectors to evade these powerful police “weapons.” But new technology in radar and lidar makes it even more difficult for drivers to beat speeding tickets. The best part is many of these innovations have reduced the number of court dates for cops because the resulting evidence is so ironclad.

To bust speeders you need to know the capabilities of the speed detector you’re using and the proper way to operate it. It also doesn’t hurt to learn about the new features available in radar and laser technology to make the job easier on you.

Radar vs. Lidar

Radar and laser speed detectors meet the same goal in different ways. Radar, the traditional form of speed measurement, uses radio waves while laser uses, well, laser.
Radar waves are emitted in a cone-shaped beam, capturing whatever vehicles fall in that wide path. The size of the cone changes depending on how close or far away the target is. This is like a flashlight appearing against a wall. The beam, or cone, of light gets wider the further away you hold the flashlight from the wall.

A laser speed gun, like a laser pointer, emits a very small beam of infrared light, even from 1,000 feet away. Because of this, it can target an individual vehicle and that vehicle’s speed.

How Radar Works

Radar, which stands for radio detecting and ranging, emits radio waves that can be bounced off cars to detect how fast they’re moving. The device looks for a Doppler shift, a difference in the wave pattern that determines if a car is coming toward or away from the detection point, as well as how quickly it’s moving. This measures the velocity and distance of the moving vehicle.

Radar shows a speed based on reflectivity, position, and speed. Based on the reading, an officer has to determine what vehicle in the “cone” of the radar is being measured. A high, clear, constant tone from the device’s speaker means a clear reading, whereas a low, wavering or raspy sound means a weak signal.

The best targets for radar are, in order, a license plate, a headlight, and a chrome bumper. This is because they are highly reflective surfaces.

Some devices have a “fastest” button that determines the fastest-moving vehicle in the cone.

When it comes to practical use, radar devices come in handheld units and “dashmounted” units. Motorcycle officers need the lighter weight handheld radar guns so they can hold them for hours on end. These devices also need long running times without being recharged.

But many handheld units can also be mounted in a patrol car. And although stationary radar guns are most often called “dashmounted,” they can also be mounted on the headliner or even on the sun visor of an officer’s vehicle. So just because you buy one type of device doesn’t mean you’re limited to a specific application.

Radar Modes

Stationary radar is the old standard. An officer sits on the side of the road and watches traffic, waiting for a vehicle moving at high speed. When he sees one, he activates the radar, which measures and displays the vehicle’s speed. The radar will give a tone. If the tone is clear and the displayed speed matches the officer observations, the officer can make the stop.

Moving radar is more complicated because the system must look for two different speeds and compare them to come up with the motorist’s speed. The radar looks for the largest object in its field and assumes this is the background. Then it looks for the second most significant object and assumes this is the target. The radar measures the difference between the target speed and that of the patrol vehicle. The radar’s counting unit uses the following formula:

Target Speed (TS) = Closing Speed (CS) – Patrol Speed (PS)

The radar unit’s display will show two speeds: the target speed and the patrol speed. The officer must make sure the displayed patrol speed matches the speed on his speedometer to determine if the reading is accurate.

Same-direction, or directional, radar was designed to eliminate the “shadowing error.” This problem occurs when a radar device mistakenly assumes a large object such as a tractor-trailer is the stationary background and miscalculates a vehicle’s speed. Same-direction radar avoids this by using a completely different method of calculation. Instead, the radar device calculates the patrol speed. Then it looks for the bounced reflection off of the other vehicle and measures the relative speed between them.

New radar guns automatically recognize which of the two vehicles is moving faster. In older models an officer must decide to activate the radar and then let the radar know if the patrol vehicle or the target vehicle is moving faster.
CONTINUED: Speed Guns «   Page 1 of 3   »

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