In March 2018, I wrote a post called “Why Do Drivers Pull Out in Front of Motorcyclists?” In that post, I reviewed and summarized 18 studies that examined factors that contributed to drivers not “seeing” an approaching motorcyclist and pulling into the motorcyclist’s path without sufficient time and distance to clear the motorcyclist’s path without causing a collision. Since writing that post, I’ve continued reading on this topic. Many times that has been frustrating…

Sometimes after a collision, a motorcycle’s speedometer or tachometer will exhibit a residual reading other than zero. In some instances, physical evidence will make it evident that the residual speed reading is not a reliable indicator of the motorcycle’s impact speed. However, if the motorcycle is equipped with a speedometer with a stepper motor, then there is the potential for the residual reading to be accurate and useful in the reconstruction.

For a three-wheeled motorcycle with two wheels in the rear, a greater percentage of the motorcycle’s weight is carried by the rear wheels and the weight transfer to the front of the motorcycle during braking is less significant than for a two-wheeled motorcycle. This changes the characteristics of the deceleration when an operator uses only the front brake or only the rear brake. The testing in this paper explores the significance of these differences.

Lane-sharing is the practice by a motorcyclist of sharing a lane with another vehicle. Lane-splitting is the practice by a motorcyclist of riding between streams of traffic by riding on or near the striping between lanes. The terms lane-splitting and lane-sharing are often used interchangeably. These practices, which are allowed in California, allow a motorcyclist to drive faster than the surrounding traffic in congested or stop-and-go traffic. They also give motorcyclists more options for how they position themselves on the roadway.

For a driver to avoid an unsafe turn in front of a motorcyclist, they need to detect the motorcyclists. If they do detect the motorcyclist, they will then need to make a reasonable judgment about the time available to complete their turn before the motorcyclist arrives at the intersection.

Day and Smith [1] reported a study of motorcycle sliding deceleration in 1984, analyzing the behavior of two downed motorcycles on various surfaces – a 1967 Honda CB305 and a 1973 Yamaha 550 Special. They towed the motorcycles using a rope with an in-line force gauge and documented the forces required to pull the motorcycles at 1 and 40 kph (25 mph). For pavement, these authors reported a sliding friction factor range of 0.45 to 0.58 during the 25 mph tests.

Crash reconstructionists are frequently asked to determine how a crash could have been avoided. In conducting this analysis, there will be instances in which an assumption will be made about the level of deceleration a motorcyclist should have been able to achieve. Based on the literature summarized here, motorcyclists would be able to achieve a deceleration of 0.5 g and above on a dry road by utilizing only their front brakes. By utilizing both brakes, most motorcyclists will be able to achieve a deceleration of 0.6 g and above on a dry road.