Methods Used to Measure Speed
Laser Speeding Tickets
Laser devices, also known as LIDAR (light distance and ranging), use a time/distance calculation to measure speed. The devices aim a narrow band of light at the target vehicle and measure the time it takes to receive the reflected light. Because the speed of both the original light pulse and its reflection are traveling at the same speed (the speed of light), differences in the time it takes the transmitted light to strike the target vehicle and return can be used to calculate the speed of the vehicle and serve as the basis for a laser speeding ticket. Unlike radar, lasers can pinpoint specific vehicles in heavy traffic.
Radar Speeding Tickets
Radar guns aim an electromagnetic signal at a target vehicle and pick up the return signal reflected off the vehicle. The doppler effect causes the frequency of the return signal to shift by an amount dependent on the relative speeds of the source of the original signal and the target. Speed radar devices measure the frequency of the reflected signal and compare it with the frequency of the original signal to determine the speed of the target vehicle. A radar beam varies in width comparative to its length-the further the radar’s “zone” extends from the unit the wider it will be. An officer who issues a radar speeding ticket should be certain that the radar was not inadvertently picking up any other moving objects that may also have been within the radar’s “zone”.
Speeding Tickets by Visual Estimation
Many speeding ticket cases start with a visual estimation. Police officers are often trained to make visual estimations. At a police facility, an officer will be asked to estimate the speed of moving vehicles while the officer is stationary and moving and the target vehicle is moving left to right, right to left, towards the officer and away from the officer. These estimations will be made while the officer is inside and outside his vehicle and through rear view and side view mirrors. Ultimately, all of the officer’s estimations are compared to the target vehicles actual speed and the officer is given a number (a “tolerance”) which indicates how accurate his estimations are on average (for example, an officer’s tolerance might be “plus or minus three”). In some cases, a visual estimate all by itself may be enough to sustain a speeding conviction. In others, it is used in conjunction with a more scientific method like radar or laser.
Speeding Tickets by Clock and Follow
Also known as a “pace”, the clock and follow method is where an officer moves his vehicle behind another, keeps a uniform distance between the two vehicles for a certain distance and then uses the reading on his speedometer to measure how fast the target vehicle is driving.
Speed Camera (photo radar) Speeding Tickets
Radar can be used to trigger a camera to photograph vehicles traveling faster than a set speed. The date, time, location, and speed are recorded along with a photo.
VASCAR (vehicle average speed calculator) Speeding Tickets
VASCAR measures speed by the use of a mobile computer which can accurately clock and calculate speed based on the time a vehicle takes to travel a known length of road.
Speeding Tickets by Aerial Speed Measurement
Police officers in aircraft measure vehicle speeds by monitoring the time it takes the target vehicle to travel between two or more marked spots on the road which are spaced a known distance apart. Information is transmitted to officers on the ground who then issue speeding summonses.