Speed Guns

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. [PAGEBREAK]
How Lidar Works

Laser or Lidar, light detection and ranging, uses a laser, or concentrated light, to measure a vehicle’s speed. Specifically, it tracks how much time it takes for the light to bounce back to determine how far away it is. It does this several times to develop a tracking history of how quickly the target is moving.

A laser speed gun shoots a very short burst of infrared laser light and then waits for it to reflect off a vehicle. The gun counts the number of nanoseconds it takes to reach the car and back, and by dividing by two it can calculate the distance to the car. If the gun takes 1,000 samples per second, it can compare the change in distance between samples and calculate the speed of the car. By taking several hundred samples over the course of a third of a second, the accuracy can be very high.

To operate a laser speed detection device, an officer points and aims the laser gun like a rifle at a particular vehicle that appears to be moving quickly. Most models feature a heads-up display with crosshairs to help aim. Then he lets the device do its work and reads the display.

The advantage of a laser speed gun is that its “cone” is very small. It’s only about three feet in diameter at a range of 1,000 feet. The disadvantages of laser guns are their higher cost and that the officer operating the device must accurately aim at one vehicle to catch its speed.

Technological Advances

As with most technology, both radar and lidar guns are tending toward smaller and lighter models. The industry has also come out with features that make the job of speed detection easier for the officer.

Carl Fors, president of Speed Measurement Laboratories, tests radar and lidar guns and instructs officers in the use of these speed measurement devices. He says the new industry standard for radar is Ka-band. Fors has seen a lot of innovation over the past 20 years, and says this is one of the many changes that has occurred within just the past five.

Other frequencies, especially K-band, are still used, but because Ka-band uses a much narrower section of the spectrum, it can operate with smaller antennas and on smaller devices. This makes it more attractive to officers who don’t want to lug a large handheld device or don’t have room for any more electronics than necessary in their already crowded cruisers.

Other innovations have reduced the errors made in calculating speed by streamlining the process for the operator.

With radar it can be difficult to find the fastest car in a group of vehicles. But now it’s easier with the function on many new models that finds the fastest vehicle in a group. Of course, with a laser you just aim at one vehicle and get a display of its speed.

 “In the past, you had to manually tell the radar gun if you were moving or stopped by keying it into a remote control,” says Fors. “If you’re in hot pursuit, you don’t have time to think about it. New guns do it automatically.

“They use a VSS (Vehicle Speed Sensor) interface. The gun itself senses whether it’s moving or stationary. This is critical in terms of what new radar guns can do. It eliminates one of the greatest errors in radar guns: shadowing. Automatically recognizing whether the device is moving or stationary eliminates that.”[PAGEBREAK]
Directional radar is another important innovation in mitigating error. Focusing only on cars going one direction (away from or toward the device) eliminates half of potential errors. If you only want to monitor cars driving in the same direction as you and your radar gun “understands” this, you won’t have to worry about the oncoming tractor-trailer in the opposite lane interfering with the radar. It just won’t get picked up by the device.

The way the radar gun does this is through recognizing radar wave patterns, or the Doppler shift. As a vehicle comes toward you it emits compressed waves, which translate to a higher frequency. As a vehicle travels away from you, the radar will register stretched waves, or a lower frequency. The radar gun can “see” the Doppler shift and recognize it. And you can hear it in the different representative soundwaves that come out of your radar gun’s speaker.

“A simultaneous display of approaching and receding vehicle speeds available from Stalker Radar is also useful,” says Fors. “I call it collision-avoidance radar. We know the problem of police cars being hit from behind. This will alert me with voice and an audible alert of someone approaching too fast. This is a feature of the company’s DSR gun.”

Kustom Signals has “fast-lock” to not just find, but also to lock the fastest vehicle. It has three windows on the dashboard: left, right, middle. Right tells how fast patrol is going (patrol speed). The window on the left tells how fast the “target vehicle” is going. Middle is the “fast” window.

Fors explains. “Say you’re in a patrol car going 60, the window on the right says 60, the window on the left says 74, and the middle says 96. So someone in the group you’re targeting is going 96. If six 18-wheelers are going 70 and a Corvette is among them, you can now see the Corvette and lock its speed. It’s called fast-lock.”

MPH Industries has come up with a way to foil those motorists who have radar detectors in their cars so they can speed with impunity. The company’s POP mode transmits so quickly that radar detectors can’t see it.

To further ensure that you catch speeders, having documentation to support your tracking history of a driver can go a long way toward clinching the ticket in court. While the courts don’t require anything beyond an officer’s report detailing how he “locked in” a speed beyond the local limit, Fors says, “If you have an in-car video representation, that’s even better.”

In fact, Fors believes the biggest trend in speed enforcement is in-car recording as documentation to back up an officer’s speed tracking.

“Now you see companies interfacing radar and laser guns with in-car video. This keeps a record that allows you to see the date, time, and speed of the suspect vehicle. I think it’s fair to the driver and the officer. I applaud that.”

Fors believes the trend is even more effective because of automatic-on technology and the introduction of DVD recorders, which can store more and can easily be recorded over if necessary to utilize even more space.

“In the past, an officer had to activate the camera system,” he says. “But new ones are on all the time, recording constantly, dumping the recording if it isn’t used. As a result, we’re getting more recordings.”

And if Fors’ prediction is right, it would be wise to take advantage of the technology now, before it becomes mandatory.

“Increasingly I think we’re going to see judges ask for documentation in the U.S., although it’s not required now,” he says. “I think it’s fair to both officer and driver.”

Overall, Fors says speed enforcement is following a familiar technological trend: “The guns are getting faster, smaller, smarter.”

Maintain Certification

Because of the technological advances being made in speed measurement devices, it’s important that officers operating them maintain proficiency in their use through certification.

Guidelines from the National Highway Traffic and Safety Administration (NHTSA) require that officers recertify every three years. Failing to follow this schedule could result in speeding tickets being thrown out.

If a judge believes an officer might have misused a radar or laser gun because he was not properly instructed or informed of the errors that can result from improper use, a speeder could walk away. And in a recent case involving a northern California agency, scores of speeders got out of tickets because the judge lacked confidence in the means used to track the motorists’ speed.

Mine Resources

To arm yourself with more information about speed detectors, visit www.theiacp.org. The International Association of Chiefs of Police (IACP) tests radar and lidar devices and posts the results on its Website under the section titled “professional assistance.”

Using protocols and performance standards developed by NHTSA and the Law Enforcement Standards Laboratory (LESL), the IACP creates its consumer products list (CPL), which includes those devices found to be in full compliance with the CPL requirements.