Here are some of the more common malfunctions and sources of inaccurate readings with radar device:. Many of these defenses are applicable only in certain situations. But, anytime an officer uses a radar to clock a driver's speed, there's the potential for a defense based on inproper calibration. Laser detectors are the most recent addition to the traffic officer's arsenal of speed-measuring devices. Built to look and act like a hand-held radar gun, a laser detector uses a low-powered beam of laser light that bounces off the targeted vehicle and returns to a receiver in the unit.
The unit then electronically calculates the speed of the targeted vehicle. Laser detectors are supposedly more accurate than radar units. One advantage for police officers of the laser gun is that the light beam is narrower than a radar beam, meaning that it can be more precisely aimed. This is true even though laser detectors use three separate beams, because the combined width of the three beams is still much narrower than a single radar beam at the same distance. This technology reduces, but does not eliminate, the chance that the speed of a nearby car will be measured instead of the speed of the car at which the operator aims the gun.
Laser detectors measure distance between the gun and the target car using the speed of light and the time it takes the light, reflected off the target vehicle, to return to the laser gun.
The detector makes about 40 of these distance measurements over a third of a second, then divides the light's round-trip distance by the time, to get the speed. This means to be accurate the officer must hold the combined beams on the same part of the car during the test. While this is easier to do with radar because of its wide beam, it is tricky to do this with a narrow laser beam.
Also, it's impossible to be sure that that the officer has been able to accomplish this feat because the officer can't see the beam. It's also possible especially in heavy traffic for one beam to hit the target car and another beam to hit a nearby car.
The chances of this happening increase with traffic density and the distance between the laser unit and the measured vehicle. The information provided on this site is not legal advice, does not constitute a lawyer referral service, and no attorney-client or confidential relationship is or will be formed by use of the site. The attorney listings on this site are paid attorney advertising. In some states, the information on this website may be considered a lawyer referral service.
Please reference the Terms of Use and the Supplemental Terms for specific information related to your state. Grow Your Legal Practice. Meet the Editors. If you want to fight your ticket, you should find out how your speed was determined. If you want to fight a speeding ticket, there are two things you must know first: whether you charged under an "absolute," "presumed," or "basic" speed law how the officer measured your speed —through pacing, aircraft, radar, laser, VASCAR, or other means.
Pacing Many speeding tickets result from the police officer following or "pacing" a suspected speeder and using his or her own speedometer to clock the suspect's speed.
Here are some things to consider for fighting a speeding ticket based on pacing: Road configuration may help prove inadequate pacing. Hills, curves, traffic, interchanges, traffic lights, and stop signs can all help you prove that an officer did not pace you long enough. For example, an officer following your vehicle a few hundred feet behind will often lose sight of it through a curve.
Similarly, if you were ticketed within feet of starting up from a stop sign or light, it could case into doubt whether the officer can prove having paced your car for a reasonable distance. The farther back the officer, the less accurate the pace. For an accurate "pace," the officer must keep an equal distance between the patrol car and your car for the entire time of the pacing.
The officer's speedometer reading, after all, means nothing if the officer is driving faster than you are in an attempt to catch up. To avoid this problem, officers are trained to "bumper pace" your car by keeping a constant distance between the patrol car's front bumper and your rear bumper.
Bumper pacing becomes more difficult the farther behind the officer is from your car. The most accurate pace occurs where the officer is right behind you. But patrol officers like to remain some distance behind a suspect to avoid alerting a driver who periodically glances at the rearview and side-view mirrors.
So if you know an officer was close behind you for only a short distance, your best tactic in court is to try to show that the officer's supposed "pacing" speed was really just a "catch-up" speed. Pacing at dusk or nighttime. Pacing is much more difficult in the failing light of dusk or in complete darkness, unless the officer is right on your tail.
In the darkness, the officer's visual cues are reduced to a pair of taillights. Also, if an officer paces a speeder's taillights from far back in traffic, he or she might have trouble keeping the same pair of taillights in view. Aircraft Speed Detection There are two ways an aircraft officer determines your speed. Here are some things to consider for fighting an aircraft speeding ticket: Ask for dismissal if either officer fails to appear.
If both officers are not in court, ask the judge to dismiss the case. If the prosecution tries to introduce an absent officer's police report or other written record into court in place of live testimony, simply object on the basis that it is hearsay. Without an officer present, the written report is inadmissible hearsay testimony. Stopwatch and reaction-time error.
If the officer's timing is not performed properly from the aircraft, the speed measurement of your vehicle won't be accurate. Since this speed is calculated by dividing distance by time, the shorter the distance your speed was measured over, the more likely it is that a timing error will result in a too-high speed reading.
For example, if the officer hesitated even slightly before pushing the timer as you passed the first ground marker, the measured time would be shorter than the true time your vehicle took to traverse the distance to the second marker. Difficulty in keeping your car in view.
If two markers are a mile apart, it takes a car doing 75 miles per hour about 48 seconds to travel between the two markers. It's hard to stare continuously at anything for that long, especially from a plane. If many other cars are on the road, it would be easy for the sky officer to lose sight of your car while looking at the flight instruments. When the radar gun and the car are both standing still, the echo will have the same wave frequency as the original signal.
Each part of the signal is reflected when it reaches the car, mirroring the original signal exactly. But when the car is moving, each part of the radio signal is reflected at a different point in space, which changes the wave pattern. When the car is moving away from the radar gun, the second segment of the signal has to travel a greater distance to reach the car than the first segment of the signal. If the car is moving toward the radar gun, the second segment of the wave travels a shorter distance than the first segment before being reflected.
As a result, the peaks and valleys of the wave get squeezed together: The frequency increases. Based on how much the frequency changes, a radar gun can calculate how quickly a car is moving toward it or away from it. If the radar gun is used inside a moving police car, its own movement must also be factored in.
For example, if the police car is going 60Kph and the gun detects that the target is moving away at 20Kph, the target must be driving at 80Kph. If the radar gun determines that the target is not moving toward or away from the police car, then the target is driving at exactly 60Kph. Police officers have been catching speeders this way for more than 50 years. More recently police started using laser guns. The basic element in a laser speed gun, also called a LIDAR gun for light detection and ranging , is concentrated light.
The LIDAR gun clocks the time it takes a burst of infrared light to reach a car, bounce off and return back to the starting point. By multiplying this time by the speed of light, the LIDAR system determines how far away the object is. Instead, it sends out many infrared laser bursts in a short period of time to collect multiple distances. By comparing these different distance samples, the system can calculate how fast the car is moving. These guns take several hundred samples per second, and they are extremely accurate.
A Radar Transmitter is a device that oscillates an electrical current so the voltage goes up and down at a certain frequency. This electricity generates electromagnetic energy and when the current is oscillated the energy travels thought the air as an electromagnetic wave. A transmitter also has an amplifier that increases the intensity of the electromagnetic energy and an antenna that broadcasts it into the air.. Basically the transmitter sends out the radar wave which strikes the moving vehicle.
The radar receiver is just the reverse of the transmitter. The receiver picks up electromagnetic waves with an antenna and converts them back into an electrical current. A radio wave is the transmission of electromagnetic waves through space.. Radar is the use of radio waves to detect and monitor various objects.
The simplest function of radar is to tell you how far away an object is distance. To do this the radar device emits a concentrated radio wave and listens for an echo or signal back.. If there is an object in the path of the radio wave like a speeding car, it will reflect some of the electromagnetic energy and the radio wave will bounce back to the radar device.
Radio waves move through the air at the speed of light, so the radar device can calculate how far way the object is based on how long it takes the radio signal to return. The speed of light is normally rounded to , kilometres per second or , miles per second. Radar can also be used to measure the speed of an object, due to a phenomenon called Doppler shift. Like sound waves, radio waves have a certain frequency, the number of oscillations per unit of time.
When the radar gun and the car are both standing still, the echo will have the same wave frequency as the original signal.
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