The police in NoVa actually commonly use one of three methods to measure the speed of moving vehicles:
– LIDAR, or Laser speed detection
– and pace
The method most of us are familiar with is radar. Radar works through an application of the Doppler Effect.
The Doppler Effect explains why the pitch of a siren coming from far way sounds different from the pitch of one close by. As sound travels through air, sound is distorted. The further the distance between your ear and the sound, the more the sound is distorted.
A police officer aims the radar gun at a target–in this case your vehicle–and the signal distortion is directly proportional to the speed of the target: the faster the vehicle, the greater the distortion. The distorted radar beam is reflected back to the radar gun and the radar gun “reads” the distortion and calculates the speed of the target.
Radar guns are generally accurate within approximately one mile per hour under normal conditions. However, numerous variables affect the accuracy of radar including calibration errors, distance and interference. The further the radar gun is from the target, the wider the radar beam and the greater the possibility of measuring the wrong vehicle or some other object that will cause interference. At a distance of 1000 feet, the beam could be as wide as 250 feet. In Northern Virginia, radar guns are checked for accuracy using a tuning fork or a calibrated speedometer. A tuning fork, vibrating at a specific frequency produces the same effect on a radar beam as a moving car. In Virginia, tuning forks must be calibrated and checked for accuracy every six months.
Most of us are less familiar with LIDAR, another method of detecting speed. (LIDAR stands for LIght Detection And Ranging.) LIDAR devices are frequently referred to as Laser speed detection devices. Essentially, LIDAR and radar are identical except that, while radar uses a sound or frequency beam, LIDAR uses a focused beam of light. When light is transmitted from the LIDAR device and hits a target, the light is reflected back to the LIDAR device. If the target is moving away from the LIDAR device, the reflected light will have a longer wavelength than it did when it left the LIDAR device. If the target is moving closer to the LIDAR device, the reflected light will have a shorter wavelength. The LIDAR device measures the distance between the target vehicle and the device hundreds of times within about 1/3 of a second and can translate the distances into a determination of speed.
LIDAR is very accurate because it uses a very narrow, focused beam of light. At a distance of 1000 feet, the beam of light is only 3 feet wide. LIDAR is more precise than radar and less likely to encounter interference from objects and other vehicles, which are the reasons why police prefer LIDAR. However, like radar, distance can affect the ability of a police officer to target the correct vehicle. LIDAR devices sight targets much like a gun or rifle and accuracy depends on the ability of the operator to properly sight the target. LIDAR devices must also be checked for accuracy every 6 months. Currently Virginia uses LIDAR devices manufactured by Kustom Signals, Inc. in the State of Kansas. The accuracy certificates used in Court are completed in Kansas by the employees of Kustom Signals, Inc. and sent to Virginia. This practice has opened the door to challenges as to the admissibility of the LIDAR certificates of accuracy.
Most of us are also unfamiliar with the third method of detecting speed in Northern VIrginia: pace. Pace is, as the name suggests, the practice of measuring speed according to the pace (speed) of the police car. A police officer will position the police cruiser at a specific point in relation to a vehicle suspected of speeding (for example, two car lengths behind) and will attempt to maintain the same speed as the target vehicle for a measurable period of time or distance.
But various factors affect a police officer’s ability to establish a meaningful pace. These factors include an accurate speedometer, speed changes due to road conditions, distance and time the speed of the target vehicle is measured as well as the location of and the actions taken by other motorists at the time of the pace. In Virginia, the traffic courts require a police officer to present a sworn speedometer accuracy certificate in order to conclude that the officer testimony is credible and that the measurement of the target vehicle’s speed is accurate.
Whether you are charged with an offense that is criminal in nature or a basic traffic offense like speeding, Traffic Court matters have serious financial and economic implications beyond the fine and costs assessed by the Court. For many people, traffic court is their first experience with the American legal system. It is a system with complex rules and procedures. A lawyer knows how to navigate through the law, the rules and the court procedures. Experienced counsel knows the inclinations of the various judges and the prosecutors.
Many traffic defenses involve complex and technical issues. A capable lawyer can assess and recognize whether the prosecution can prove its case. A lawyer can advise you regarding viable defenses; help you present defenses that work; and, when appropriate, can negotiate a satisfactory plea bargain. A lawyer can protect your rights and prevent you from being taken advantage of by an overloaded or impersonal legal system. A lawyer can help you obtain a restricted driver’s license if you are qualified for one. In short, a lawyer is your ally in a complex and often hostile system.