In addition to Robs post about the M25 I'd like to point out that in some parts of the country (UK) there are some very special speed cameras!

These units actually calculate your average speed between two points and if it's over the limit they snap you and you will be fined/prosecuted - depends on the nature of the speeding. Rather nasty if you ask me. Most drivers just slow down for the normal speed cameras and speed up in between - can't do that with these.

M