Lidar devices can be used only in stationary mode. They typically feature a crosshair sight or a targeting dot.
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Law Enforcement Officers everywhere eventually find themselves involved in traffic enforcement. Speed detection and enforcement are critical aspects of this duty. Pacing, time/distance formulas, radar and lidar are valuable speed detection tools, but to choose the method your agency will use, you need to understand the strengths and weaknesses of each method and know what to look for when selecting equipment.
Observe and Quantify
In general, speed detection and enforcement involve one or more of four general methods. The first two methods require only basic observations and math.
Known as pacing , the first technique involves following a suspected violator for a reasonable distance at a known speed. The officer then makes a determination of the violator's speed using the patrol car's speedometer. One of the many potential pitfalls of this method is an inaccurate patrol car speedometer. This can be rectified by checking the speedometer against a known distance using a calibrated stopwatch. The officer travels a mile at 60 mph. The officer should travel through the distance in 60 seconds. This test verifies the patrol car speedometer for 60 mph. Some courts will accept this as a reliable citation based on totality of the circumstances; some will not.
The second technique uses a time/distance formula to create a speed chart . The mathematical formula is: Speed = Distance/Time
This technique is often used for special project speed enforcement. A known distance is marked on a roadway, (usually 300 feet in a city or 600 feet on a freeway) and a calculation is used to determine speeds of vehicles traveling through the speed zone. For example, using 600 feet for a known distance, if a vehicle travels through the zone in 8 seconds, its speed will be 75 mph (75 mph = 600 feet/8 seconds). The officer must be in a position to observe each vehicle's entry and exit into the speed zone; consistently use the same point on the vehicle to start and stop the stopwatch; and use a calibrated, certified stopwatch for this activity. This type of speed determination isn't accepted in all states. If unsure, check with the prosecuting attorney representing your area.
The third technique is radar. Radar has proved an effective tool in speed detection and enforcement. Many departments have one radar unit per car because the cost of the radar unit is often recovered through citation revenues. Of course, officers don't write speed tickets to generate revenue; they issue speed citations to correct behavior, save lives and detect and deter crime. However, revenue can cover the cost of basic equipment very quickly if proper laws are passed, agreements are reached and protocols and policies are followed.
Radar operation has its pros and cons. Advantages include:
- Cost: It's affordable for most departments;
- Availability: Departments can
easily issue one radar unit per vehicle; and
- Multiple mode enforcement: Radar can effectively capture speed in both the moving and
The acronym VAR(S) explains what the radar operator must know. The "V" stands for a visual estimate of the target vehicle's speed. The officer must stay alert and remain in a state of constant vigilance while on duty, which allows the officer to observe traffic and select those target vehicles that are speeding.
Once the officer has identified the target vehicle and estimated the target vehicle speed, the officer should activate the radar equipment and listen for the Doppler audio pitch - the "A" in the acronym. The Doppler pitch must coincide with the officer's visual estimation. The Doppler audio pitch is more than useful; it's critical in assisting the officer in observation and identification of the target vehicle.
The next step in proper radar operation is to check the radar display to verify that it matches the officer's visual estimate of the target vehicle speed and the audio confirmation. These three steps must be taken in every situation in which the officer elects to take action on a speed violator in stationary mode.
In moving mode, when the officer is actively moving around a patrol area, the officer must add the "S" to complete the VAR(S) process and match the radar patrol display against the speedometer . At times, the patrol speeds on the radar display are inaccurate due to an angle error, which can result in inaccurate, low Doppler or patrol speed verification. This could reflect negatively on the target vehicle. If there is any discrepancy in any aspect of the VAR(S) process, a citation should not be issued.
If the VAR(S) steps are followed properly, the officer can write a citation. However, some other factors could affect the radar's accuracy. Radar units transmit radio energy that travels at the speed of light. The radar beam is typically 12-18 degrees wide, and is conical, 3-D in shape, with rough, irregular edges. Radar energy is transmitted indefinitely until it is reflected, refracted or absorbed. Each radar operator should be aware of what angle the radar unit transmits. (This information is readily available through the manufacturer of the radar equipment; have the model and serial number available.) A known angle allows the officer to verify that the target vehicle was within the radar beam at the time of detection. The greater the distance from the radar antenna, the wider the radar beam, thus increasing the violator pool.
Radar units should be checked and calibrated by a factory authorized technician once every three years. Ensure the checkup includes the radar antennas, the counting unit and tuning forks. The antennas should be positioned to point ahead and slightly down to avoid the potential for angle error in the radar reading. Ensure you are familiar with the operating instructions of the unit; failure to do so could result in an embarrassing courtroom experience.
Lidar is the fourth common speed detection technique. Lidar units operate using light transmission and reception. Infrared light waves are transmitted from the lidar device to the subject vehicle, and the difference in transmission and reception time is calculated by computer. Lidar devices are typically handheld and can be used only in stationary mode. They typically feature a crosshair sight or a targeting dot, allowing the officer to aim at a license plate or other reflective surface. Lidar devices may be operated by battery or wired to run from a cigarette lighter. As with radar, visual estimations must be performed by officers prior to targeting a speed violator with a lidar unit.
The real advantage of lidar is its ability to pinpoint potential offenders. Because the lidar beam is very narrow - unlike radar's conical projection - an officer may select the target vehicle from a pack of vehicles in congested traffic. Lidar devices can detect whether a vehicle is traveling toward or away from the officer. They are lightweight, easy to use and accurate - an excellent speed detection tool for motor units, as well as patrol units in all areas.
Sum and Substance
When selecting traffic enforcement options, consider the following: First, what's the focus of the enforcement, rural or urban? Next, what are the traffic flow patterns? Then, determine if stationary or moving operation is most desirable. Finally, weigh the cost of each device.
The bottom line:
All speed detection techniques can be effective, if the officer is aware of the basic rules and operation procedures they require.