On my way home from work I join a roundabout under a dual carriageway from a minor road, all in a 40mph speed limit area. Vehicles already on the roundabout appear at speed from under the bridge indicating left. In most cases they don't want the road I am on but the next one, an ajacent motorway slip road. I have seen many near misses and several crashes because cars appear to 'flash' the waiting traffic, the drivers believing the car is going to exit into the minor road. In truth they want the motorway, have indicated left too early and the darkness under the bridge has caused their automatic headlamps to switch on/off very quickly.