As we seem to be discussing motorways, toll roads etc at present I though I would throw this recent observation into the pot.
Returning home along the M18 yesterday I observed two uniformed police officers climbing down from the cab of a silver Mercedes tractor unit, no trailer attached, just the tractor unit.
It appeared that in conjunction with a marked traffic car they had just stopped two artics on the hard shoulder. I had heard tell of the police using such vehicles so as to observe (and capture on video) what truck drivers are doing, such as reading books or watching videos whilst driving, but had never seen it for myself before.
Mike