On Roadway 和Off Roadway；
Off Roadway是NHTSA定义，指的是车跑出路后撞上树墙。。。。
A run-off-road (ROR) crash occurs when a vehicle in transit leaves the road and collides with a
tree, a pole, other natural or artificial objects, or overturns on non-traversable terrain. This type of crash usually involves only a single vehicle.
NHTSA有博士研究这东东
https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/811500
