We had a case involving a cyclist who is hit by a turning driver. One of the issues which developed was whether the cyclist was stopped or moving at the time of impact. Our client was using a GPS device which we had examined by a forensic expert. What we learned was both interesting and surprising.
GPS is very accurate when a bicycle is moving, particularly at cruising speed. The data they produce will allow you to track the cyclist’s exact location on the road. Here’s how it works. Every four seconds the typical GPS calculates the exact latitude and longitude of the unit creating a data point. An algorithm then calculates speed and distance traveled between data points.
GPS, however, is not as accurate at very slow speeds (2-3 MPH) or when the cyclist comes to a stop. Tracking the data points at low speeds may appear to move the track dramatically. It can be even worse when it comes to a stop, fluctuating wildly, perhaps putting the data points way off the road or even across an intersection. Experts explain this is one of the inherent issues with GPS. Golfers using a handheld GPS device on the golf course have probably noticed the same thing.
While GPS can be extremely accurate, when used as evidence, its limitations sometimes force us back to relying on eyewitness testimony and circumstantial evidence at the scene.