HOW AN OFFICER MIGHT DETERMINE YOUR SPEED

Virginia allows officers several methods to determine a vehicle’s speed which includes the use of radar, lidar or pace. The following scenarios illustrate these three methods of speed determination.

Scenario 1: Radar Cases

Radar use by Virginia law enforcement is a well established technology that is authorized by Virginia law and frequently used.  When driving into Virginia from another state, one of the first signs to appear is the “Radar detectors are illegal in Virginia” sign.  Virginia is one state that has outlawed the use of radar detection devices.  Typically an officer will use radar in either stationary or moving mode. When in stationary mode, an officer will be stationed in a stationary position off the road and monitoring traffic. When in moving mode, the officer may determine a vehicle’s speed even while the officer’s vehicle is also in motion. Depending upon the case specifics, how to approach a radar case will depend on whether the officer is in a fixed position or in motion. 

One inherent weakness of radar is that it typically does not distinguish a specific vehicle.  If multiple vehicles enter the radar’s field at the same time, it becomes the officer’s challenge to determine which vehicle is registering a particular speed.  For this reason, officers usually create a visual track history of the vehicle prior to its entry into the radar stream, but only if the officer is paying attention. 

As with any mechanical device, after time, its accuracy may become compromised.  Radar is no exception.  Virginia code requires that radars and other speed determination devices have their accuracy frequently checked to make sure there are no flaws with the device which may then taint a reckless driving or other speeding case.  It is important to make sure the officer has properly checked the radar’s accuracy and has the documentation to back it up.  Of course, this documentation is not self-explanatory and can take some technical understanding to figure it out. 

Scenario 2: Lidar Cases

Lidar or laser technology is the most recent innovation in speed determination technology.  This technology is currently used in Virginia as a method of determining vehicle speed and is accepted by Virginia courts as a valid speed determination device.  Unlike radar, laser technology has the benefit to law enforcement as being vehicle specific.  In other words, in a typical Lidar case, the officer will maintain a fixed position off the road and will aim the device at a specific vehicle with the assistance of a viewfinder on the Lidar device.  Lidar then measures the distance of the vehicle from the point of the device through laser technology and then by using the simple mathematical formula of rate x time = distance, calculates the speed of the vehicle measured. The Lidar device will typically show two readings: the vehicle’s speed and the distance measurement of the vehicle from the device.  It is significant to take note of the distance measurement as Lidar’s accuracy may become compromised at greater distances.

Like radar, Lidar requires frequent checks to make sure it is functioning properly so as to avoid wrongful convictions in reckless driving cases.  While Lidar can be an accurate device, it is not without its flaws.  As with radar, it is important to make sure the officer has properly checked the device for accuracy and that the officer has the proper documentation to back it up.             

Scenario 3: Pace Cases

Pace cases differ from radar and Lidar cases in that the officer is determining the target vehicle speed not through a speed determination device, but rather through the officer’s own speedometer.  In this typical scenario, the officer will usually be operating an unmarked police cruiser and will follow the target vehicle for a distance of at least 2/10 th of a mile.  To get an accurate speed reading, the officer should be behind the target vehicle and maintain equal distance between the cruiser and the target vehicle. 

While pace cases are accepted in Virginia courts as a legitimate method of determining vehicle speed, pace cases are more prone to human error as they rely upon the officer’s ability to multitask and accurately determine a target vehicle’s speed.  Flaws with a pace case may include the officer determining a target vehicle’s speed while accelerating to catch the target vehicle, conducting the pace while parallel to the target vehicle as opposed to behind and not conducting the pace for an adequate distance to obtain an accurate speed reading.  However, even in a pace case, it’s important to make sure the officer can establish the accuracy of the cruiser’s speedometer.