3 Tech Flaws Inherent to Traffic Radar Design: Exposed by a Virginia Reckless Driving Attorney

It is no secret that in most states, radar technology has long been used by police departments to issue tickets. Some states use cameras (such as Maryland), but regardless of how one is caught, the risks are greater in some states — such as the Commonwealth of Virginia — where 20 over the limit is a crime. Furthermore, there are relatively low speed limits in some portions of the most populated county in Virginia, Fairfax County.

Why care about radar technology flaws?

In the Northern Virginia, D.C., and Southern Maryland area, many people have government jobs, or are working for federal contractors. Security clearances are a big issue, including the maintenance of status as well as the ability to obtain one. A criminal record can cause issues in some cases.

The good news is that the primary way police officers in Virginia (state level, county, and city) determine a target vehicle’s speed is through the use of technology… and technology is not perfect.

Devices used to commonly measure speed in Virginia includes:

  • Stationary Radar
  • LIDAR (a radar laser device relying on pulses instead of Doppler)
  • Moving-Mode Radar (radar located in a police cruiser)

Radar devices suffer some of the same inherent flaws as their laser-based counterparts; in other ways, radar devices have flaws which are eliminated by the introduction of laser technology (and vice versa). The same is true for stationary radar vs. moving-mode radar. You can learn more from a local Fairfax reckless driving attorney who explains in great detail, the variations in ways to challenge accuracy depending on device. This article provides an overview of traffic radar, not laser radar.

Fairfax County is the largest (most populated) county in Virginia. Many, many reckless driving charges arise each week (for sake of comparison, it is often comparable to the number of possession of marijuana charges for that time period). It could be due to the Dulles Airport and surrounding roads, including the Fairfax County Parkway (route 267), and other trouble spots such as I-66, I-95, 295, 395, and 495.

3 Ways a Northern Virginia Reckless Driving Attorney Might Challenge a Radar Reading

Operator-error and tech flaws are often different and unrelated topics, but on occasion, an operator-error is induced by a technologically rooted flaw. And in that same light, a flaw may become exposed or made worse by operator-error. The following three are more related to the technological flaw issues: margin of error; harmonics; and, speed tolerance.

For purposes of the following 3 technological flaws of traffic radars: Margin of error means exactly what it sounds like, and needs no background introduction. “Harmonics” refers to stray echoes — or, return signal frequencies — when radar is used. “Speed tolerance” has to do with the rate at which a vehicle increases or decreases in speed.

Margin of Error

Some stationary radar devices (i.e., side of road speed trap) have a margin of error of about 1 mph.

Moving-mode radars are radar devices inside of a police-cruiser. These units may have a higher margin of error, because not only do they rely on signals from the target vehicle, but the cruiser speed, as well. (the cruiser speedometer is not perfect and has a margin of error of its own, thereby increasing the overall margin of error for a moving-mode device in relation to a stationary unit). The margin of error is about 2 mph, in many cases.

In a close case (for example, a 55 mph zone where it is alleged the defendant traveled at speeds of 75 or 76 mph) the margin of error may be an issue well worth defense counsel’s examination and attention.


Harmonics may be thought of as false signals as a result of amplified, stray echoes. Large objects — particularly those that are long, flat, and continuous — may lead to this effect. When this technological flaw is present, the speed reading on the radar device could be many times higher than the true speed of the vehicle.

Speed Tolerance and Change in Speed

Radar uses frequency measurements to determine reflections echoed from a wave bounced off of an object in motion. The time it takes is the:

Radar Integration Cycle

The ability of the radar to track and process speed accurately depends on its’ speed tolerance: if a vehicle changes speed at a rate greater than the traffic radar’s speed tolerance level, the result may not be accurate at all. For example, if a vehicle stops at a rate of 1 mph or more per radar integration cycle (often this is about a tenth of a second, but some older devices could be 2 seconds), then accuracy issues are likely present.