Comparison of Drag-Sled and Skidding-Vehicle Drag Factors on Dry Roadways 2006-01-1398

Lightweight “drag sleds” have long been used by crash investigators to determine the “drag factor” at a crash scene. Despite this long history, no published work has ever shown a correlation between drag sled results and the skidding performance of vehicles on multiple “uncalibrated” surfaces. Indeed, some researchers have noted that their testing appeared to show a poor correlation between the two. It has become clear in recent years that the interaction between braking or skidding tires and pavement does not fit the simple weight- and speed-independent friction model that has been assumed, leaving the accuracy of drag sleds in doubt. This paper presents the results of several comparison tests at different locations, involving multiple skid-test vehicles, dozens of drag sleds of various designs, and more than a hundred “pullers,” and attempts to correlate the results of the two methods. Drag sleds tended to read higher than even the peak value generated with skidding cars, though occasionally this was not the case, and no relationship between individual drag sled results and skidding vehicle results could be identified which applied across multiple surfaces.