What Is AVL Data?

AVL stands for Automatic Vehicle Location.

AVL data is data that is automatically collected that relates to the location of a vehicle. Most police vehicles are equipped Computer Aided Dispatch (CAD) systems. Many of these CAD systems include AVL systems which allow the law enforcement agency to track the locations of their vehicles.

These AVL systems can use either GPS (global positioning system) satellites or cell towers to track vehicle locations. GPS-based systems are far more reliable because a GPS signal can be maintained almost anywhere on the surface of the planet. Cell tower based systems on the other hand depend on the ability of the system to maintain contact with cell towers. In remote areas this can be problematic and can produce large time gaps in data.

For example, Arizona Department of Public Safety (AZDPS) and Peoria Police Department vehicles are GPS-based. Some of the Maricopa County Sheriff’s Office vehicles use cell tower based systems. The AVL systems only record data when the CAD system is operating. For example, AZDPS motorcycles are equipped with AVL systems, but when the AVL systems only collects data when the motorcycle is stopped and the trooper’s computer is open. AZDPS troopers turn off their computers when in motion and therefore do not collect AVL data when moving.

The data available from these systems varies, as does the format. Some data sets are very detailed and for each data point include: time, GPS coordinates, heading, and speed. Data points are typically taken every few seconds, but may be several minutes or more apart. Other data sets may lack some detail. For example, we have seen AVL data that does not include GPS coordinates, but instead has a description, like Tatum at Shea, that gives a rough location.

Some law enforcement agencies are now using systems that integrate in-car cameras with AVL data. When we request AVL data, we might get a video with embedded data. The video will show the view out of the law enforcement vehicle’s windshield, and will also display the vehicle’s speed and GPS coordinates.

How is AVL data helpful in a criminal traffic case?

AVL data is most relevant in criminal traffic cases that involve an allegation of speeding where the speed was measure by “pace”. When a speed is measured by pace, it means the officer supposedly followed the driver and matched the driver’s speed, thereby determining the driver’s speed by pacing the driver at the same speed. If the officer did indeed do that, we would expect the AVL data to show the officer in the location of the alleged violation, at the time of the alleged violation, and traveling at the alleged speed. If the AVL data does not match the officer’s allegations, then we have a factual argument that the officer was mistaken or that the allegation is not credible.

Requesting AVL data can be helpful in other ways too. For example, consider an excessive speed case where the speed was determined by pace. We always request AVL data. If the prosecution fails to disclose the AVL data, we ask the court to dismiss the charge because the prosecution has violated its disclosure obligations.

In another example, we had a case wherein the prosecution disclosed the AVL data, except the data right for the time when the violation supposedly took place was conveniently missing. No one from the State could explain why. We were able to leverage that to get the charge dismissed.

What do we do with AVL data?

When we get AVL data, we always take the GPS data and overlay it on a satellite view of the roads. This is very helpful for visualizing where the officer was and how fast he was going. It can also be a good tool when presenting the information to a not very tech savvy prosecutor or judge. Here’s what it might look like:

When is AVL data not helpful?

If we got, for example, a dash camera video with embedded AVL data that shows the police officer traveling at the speed limit, then shows the defendant fly past the police officer, then shows the police officer accelerate to catch up to the defendant, then shows the police officer pace the defendant at 100 mph for a mile or two before initiating the traffic stop, that is not helpful.

It can also be hard to argue that AVL data is relevant when the speed is obtained by LiDAR or radar. LiDAR is only used when the officer is stationary. So when the speed is determined by LiDAR, there is generally no pacing involved. Radar can be used while the officer is moving or stationary. Sometimes AVL can be relevant in a radar case if the officer says he followed the driver, essentially pacing and using radar simultaneously. If the speed was measured by radar while the officer was stationary or traveling in the opposite direction, AVL is less relevant.