on one stretch of the m27 for more than a day. also in we spoke to someone inside national highways. he works on smart motorways and he says he no longer trusts the kit. happens all the time. sometimes it's faulty, sometimes they're repairing something and they'll turn it off. do you trust the radar? no. why? because i've seen it fail too many times. national highways says safety is its highest priority and there are well—rehearsed contingency plans to deal with power outages. our data shows they are needed. a network with hundreds of dangerous failures. richard bilton, bbc news. panorama's smart motorways: when technology fails is on bbc