Skid marks on the road?

[Hudson]

I often see skid marks on tarmac on narrow twisty country lanes.  You know the type, the ones with a sharp square edge at one end and a feathered edge at the other end. But as they are often in the middle of the road it isn't obvious in which direction the skidding vehicle was travelling.  Any ideas?

[Grunty]

In the case of a collision, the square end would often be where the vehicle stopped.  Another common reason for skid marks is the brakes beconing locked on a lorry, or more often a trailer.

[ezapf]

...and the sharp end will be at the beginning of a peel-out if some hotrod decides to see how fast he can go from zero to sixty.