Used to be one on the Bristol ring road, though I've not been that way for 4 or 5 years. They want to trial one on the M3, I think between J4 and J2 (Frimley and M25 interchange), but due to the morning queues being about ten miles long these days there there's still some head scratching going on. Last suggestion I heard, and being seriously considered as well, was to use the hard shoulder as a fourth lane

. That's a stretch of motorway ten or so miles in length with no hard shoulder... barking. The hard shoulder is needed for emergencies and they want to do away with it. How many times do emergency vehicles find it handy to nip up the shoulder to get to an incident quickly? What about the breakdown companies who would otherwise have their operators working in L1 (and working on the hard shoulder sounds dangerous enough). Or the lorry driver who died after a brick was chucked through his windscreen but managed to get his artic safely on the hard shoulder - that was on the same stretch of the M3 that they want to try the HOV lane on. Imagine how much worse that incident could have been if the poor driver had no hard shoulder to go to.