A Comparison of Devices Used to Measure Vehicle Braking Deceleration

Accident investigators rely on a wide range of methods to measure or quantify vehicle braking deceleration. Generally, this information is applied to define a “drag factor” or “coefficient of friction” for a skidding vehicle. Methods employed can include everything from simple estimations based on past experience and individual expertise to testing using sophisticated devices.

This paper is a compilation of data from a series of skid tests comparing some of the methods and equipment currently available. These tests were performed with an assortment of vehicles each equipped with or monitored by a selection of devices designed/applied to quantify some combination of time, distance and velocity. The devices tested include two models of “fifth wheels,” the Vericom VC2000, the g-analyst, a bumper detonator and shot timer, doppler RADAR, an infrared timer device, and a drag sled. The data from each of these skid tests is then provided for the reader's comparison and analysis.