We've already seen plenty of evidence of the potential damage that sat navs can cause, but the UK's Network Rail has now put a figure on at least some of it, saying that the devices are responsible for damaging some 2,000 bridges per year and causing 5,000 hours of delays. That, thankfully, is not from the satellites falling from the sky, but rather from over drivers relying a little too heavily on GPS units (in particular those driving trucks too large for the bridges), a problem apparently so bad that some places in the UK have taken to putting up signs warning of the dangers. That's apparently not quite enough to solve the problem, however, and now , in addition to warning people to use a little common sense, Network Rail is also reportedly attempting to map all of the UK's low bridges and level crossings so that the information can be added to GPS software.