I heard a discussion of radio 4 about these a few months back. Essentially the first one the M42 had emergency lay byes every 600m so there was a very good chance that a broken down vehicle could make the lay bye and safety, and the results showed that this was quite effective. Now they have stretched the lay byes to every 1800m - 2000m with the cameras and gantry's also further apart. The result being that vehicles cant make the lay byes and are not being picked up by cameras with lanes not being shut. The delay is something like 13-17mins between a vehicle breaking down and the lane being shut.
To make things worse I have spotted in many places including the M6 they have stopped vehicles actually pulling onto the grass verge and getting off the live lane by installing miles of continuous armco barriers. All in all this makes motorways more unsafe than dual carriageways as drivers don't expect to see broken down vehicles in lane 1, Most dual carriageways dont have armco barriers all the way down the side thus allowing a broken down vehicle to pull onto the verge. Finally many drivers are becoming aware of these dangers and are simply not driving down lane 1, rendering null and void the whole point of smart motorways which was to increase capacity.
Their current design will be abandoned very shortly and changes made. They are simply much more dangerous and stats show this.
