Sentence:  The main argument for the use of culpability as a categorizer is that some accidents can be said to be independent of the behaviour of at least one of the drivers, for example, being <WSD>shunted</WSD> when having stopped for a red light (in a slow and controlled manner, at least). 
Meaning of the word marked with <WSD> tags:  To have a minor collision, especially in a motor car.