Testing Methodology to Evaluate Reliability of a “Frozen” Speedometer Reading in Motorcycle / Scooter Impacts with Pre-Impact Braking

A number of methods have been presented previously in the literature for determination of the impact speed of a motorcycle or scooter at its point of contact with another, typically larger and heavier, vehicle or object. However, all introduced methods to date have known limitations, especially as there are often significant challenges in gathering the needed data after a collision. Unlike passenger vehicles and commercial vehicles, most motorcycles and scooters carry no onboard electronic data recorders to provide insight into the impact phase of the collision. Recent research into automobile speedometers has shown that certain types of modern stepper motor based speedometers and tachometers can provide useful data for a collision reconstruction analysis if the instrument cluster loses electrical power during the impact, resulting in a “frozen” needle indication. Given the size and weight of motorcycles, and the location of speedometer and tachometer electrical connections in vulnerable areas of two-wheeled vehicles, this methodology appears particularly promising for application to two-wheeled vehicles. There has been little published research or testing specific to speedometer readings in motorcycle / scooter impacts. Because many motorcycle and scooter collisions are immediately preceded by a driver braking input, it is also important to understand the effect on the speedometer readings in cases with evidence of pre-impact braking or locking of the speed-sensing wheel(s). This paper introduces the basic concepts of speedometer design and function, discusses the current literature on the technology’s broader use in accident reconstruction, describes the procedural steps that should be taken by an investigator in order to determine whether a frozen speedometer indication is likely to be reliable, and presents the results of a series of tests conducted on a wide variety of popular motorcycles and scooters regarding their speedometer function in electrical power-loss situations, particularly in the event of pre-impact braking.