MadEngineer: A number of years back and before the time that everyone had cell phones I was visiting some friends and another couple were late but eventually turned up.  They had lost control on a slight bend in Taranaki ending up in a ditch and suspected black ice.  Conditions at the time were agreeable.  Police charged them with reckless driving (IIRC) and were not interested in checking the road surface or even listening to them at all.  The attitude was if you've come off the road you were simply not driving to the conditions no matter the road surface.