Namely when you are lying on the road in front of one. Questionable bike maintenance meant that as I pulled away from the lights in Caversham this morning my chain ceased to be a loop and did its 'tied in knots' act after a link snapped. Over the bars I went. As I lay on the floor I noted how big a car look as it looms over you, even a little Saxo. Thankfully they did not run me over.