She was unlucky it wasn't the weekend when all the pending prosecutions were quashed as the camera was uncalibrated at the time.
Apart from motorway bridges, most of the sites that are used are fairly static, and you soon get used to where they are.
A list may be found
HERE. Not that I would ever speed, but it prepares you for Richard Heads flying past you, then suddenly pulling over in front of you and slamming their brakes on for no apparent reason.