One of the freeways I use is adding a carpool lane. To do this, the breakdown lane was removed. There is no shoulder, or place to push a car off the road if it breaks down. From a traffic flow standpoint, which is better, three lanes and a carpool lane or three lanes and a breakdown lane? Under perfect conditions, I can see the benefits of a carpool lane. When a car breaks down, however, I can see three lanes being turned into two lanes, with traffic being backed up for miles as everyone tries to merge.
From someone who visited the breakdown lane yesterday, I say screw the carpool lane. We need to be safe if we have to pull over for any reason. It cannot be assumed that every single traveller on a road will make it to their destination without the urgent need to stop.
Yesterday morning, I wouldn’t have even cared about this but after my 2 year old car overheated (badly) :mad: and I had to spend 45 minutes on the side of the Mass Pike :eek: , I’ve decided that carpool lanes are unnecessary.
Anyway, as far as I know, Massachusetts doesn’t have any carpool lanes so I don’t think I need to worry. 
I’m pretty sure there are no carpool lanes at the exclusion of a path for emergency vehicles, except on bridges, where I believe the carpool lanes vanish anyway.