Analysing Runoff Road Crashes
A RUNOFF ROAD CRASH TYPICALLY INVOLVES A SINGLE VEHICLE LEAVING THE INTENDED TRAVEL PATH. IN MOST CASES, THE ERRANT VEHICLE MAY ENCROACH ONTO THE ROADSIDE AND COLLIDE WITH ROADSIDE FURNITURE APPARATUS DURING THIS DEPARTURE PROCESS.
Arunoff road crash is generally categorised into two groups: off-road crashes and on-road crashes where the vehicle remained on road after the crash. In analysing runoff road crashes, there are few important issues that need to be considered. First and foremost is physical evidence pertaining to road marking evidence commonly associated with runoff road crashes. In a classic ‘fish-hook’ crash, where the driver exerts excessive steering input during a crash avoidance manoeuvre, evidence of a yaw mark is expected on the crash site. A yaw mark is different from a regular braking mark. A yaw mark is a scuff-mark made on a surface by a rotating tire, which is slipping parallel to its axis. A yaw mark is typically less perceptible to detect, less dense than a normal braking mark and relatively does not last long. Yet, it is one of the important evidences in analysing a runoff road crash. It not only helps the crash investigator resolve some of technical issues, such as critical speed of the vehicle before crash or any possibility of road defect and design, it also helps explain driver behaviour before the crash takes place. For instance, examining the exit angle of tire marks leaving the roadway in a runoff road crash may reveal driving performance before the crash. An abrupt exit angle of the tire mark may indicate a sudden manoeuvre in avoidance of an obstacle on the road, while a shallow exit angle (yet an unusually long tire mark) may imply the driver fell asleep a few seconds before the crash. The second issue is physical evidence pertaining to the severity of the injury from the crash. One of the leading factors that increase the injury severity in runoff road crashes is that it usually involves striking a roadside object. The collision is extremely hazardous, as these usually involve narrow impact and non-absorbing energy structures. Specifically, this type of collision is characterised by lack of stopping distance, massive deceleration of force experienced by the victim and intrusion of a roadside object inside the passenger compartment. The most commonly struck roadside objects are a natural or planted tree, a guardrail, poles, bridge parapets and concrete barriers. It is also worth mentioning that some