I first put this in the "Four cyclists..." thread -
http://www.safespeed.org.uk/forum/viewtopic.php?t=5487 . However in deference to the importance of issues there, I have moved it to here.
A few (perhaps 6) years ago in sub-zero but dry conditions on my way home, I noted a "police slow" or "police accident" sign on approach to a sweeping bend. I slowed to a snail's pace knowing the temperature. Glad I did. A water main had burst and laid a slick track for approximately half a mile. At least three had separately skated off in various directions.
Several people were in tears - but all thankfully over mangled metal.
The solitary policeman was sitting on blues at the other end of all this - he had had only one sign and deposited that at the other end and was using his blue lights as the warning at the other end. This was all only about half a mile from my home. I brought a flask of tea back for those shivering in ther wrecks awaiting recovery. I suggested that the road should be closed off and diversions put in place pending recoveries and gritting, but the policeman was adamant that that was neither necessary nor overall a good thing (he was more concerned at getting people lost). In practice the diversion would have been straightforward, but it is probable he'd come from further afield and didn't know this.
Despite the signs and blue lights, while I was chatting to the copper a motorist (rwd Cavalier) having ignored the sighn came hurtling towards us on locked wheels. He just managed to catch it using Ripley's recovery technique took his foot off the brake on nearly full lock at the bend just through the ice and caught the rear swing. A good recovery by a total plonker - but glad he did or he'd have taken my car with him. Prat.
I don't know how thinly stretched the police were at the time, but IMHO there should have been blue lights at both ends of this carnage/slick. It was about half a mile long with three or four spinoffs.