I’m always reluctant to use the hard shoulder when it’s open as a lane after an incident my mate had about 6 months ago near Birmingham. A woman in the first lane (not hard shoulder) broke down, she panicked and pulled onto the hard shoulder straight in front of my mate and slammed on. He was fully freighted but luckily he was going slow and literally just touched the back of her car but could easily have been much worse. I’ve seen a lot of broken down vehicles and no warnings on the gantry.
Also the other thing that annoys me, like others have mentioned, is when the speed limit is suddenly displayed for no reason. You can be the only vehicle on the road in the early hours of the morning and suddenly there will be one gantry displaying 40mph and it always seems to be one with a speed camera on it.
mm1988:
I’m always reluctant to use the hard shoulder when it’s open as a lane after an incident my mate had about 6 months ago near Birmingham. A woman in the first lane (not hard shoulder) broke down, she panicked and pulled onto the hard shoulder straight in front of my mate and slammed on. He was fully freighted but luckily he was going slow and literally just touched the back of her car but could easily have been much worse. I’ve seen a lot of broken down vehicles and no warnings on the gantry.
I have to on those dual carraigeways with no hard shoulder/verge.
What really gets my back up with these smart motorways is the sudden changing of the gantries. The amount of times I’ve been trundling along at 50mph fully loaded (sometimes pulling a decker), the gantry in front is showing 50, get about 100 yards from it and the b######d thing changes to 40. You then have a split second decision to make. Keep going and hope the camera doesn’t flash, or slam the brakes on your 44tonnes of lorry in an attempt to drop 10mph in less than 100 yards. Having seen the consequences of another lorry attempt the latter on a rainy day on the M6 last year (remarkably the drver managed to regain control without touching a single other vehicle or barrier etc. but I bet he pulled into the next services to change his underwear) I always just hope for the best now if I deem it past point of no return. It’s not a very well thought out system in my opinion and I think people have to pay so much attention to their speedometers and watching the gantries for sudden changes its taking their concentration away from the road and traffic around them. 
mickyfred:
What really gets my back up with these smart motorways is the sudden changing of the gantries. The amount of times I’ve been trundling along at 50mph fully loaded (sometimes pulling a decker), the gantry in front is showing 50, get about 100 yards from it and the b######d thing changes to 40. You then have a split second decision to make. Keep going and hope the camera doesn’t flash, or slam the brakes on your 44tonnes of lorry in an attempt to drop 10mph in less than 100 yards. Having seen the consequences of another lorry attempt the latter on a rainy day on the M6 last year (remarkably the drver managed to regain control without touching a single other vehicle or barrier etc. but I bet he pulled into the next services to change his underwear) I always just hope for the best now if I deem it past point of no return. It’s not a very well thought out system in my opinion and I think people have to pay so much attention to their speedometers and watching the gantries for sudden changes its taking their concentration away from the road and traffic around them.
There is a time delay between the speed limit changing and the cameras enforcing it, im sure someone else on here mentioned 30 seconds, but dont quote me on that 
mickyfred:
What really gets my back up with these smart motorways is the sudden changing of the gantries. The amount of times I’ve been trundling along at 50mph fully loaded (sometimes pulling a decker), the gantry in front is showing 50, get about 100 yards from it and the b######d thing changes to 40. You then have a split second decision to make. Keep going and hope the camera doesn’t flash, or slam the brakes on your 44tonnes of lorry in an attempt to drop 10mph in less than 100 yards. Having seen the consequences of another lorry attempt the latter on a rainy day on the M6 last year (remarkably the drver managed to regain control without touching a single other vehicle or barrier etc. but I bet he pulled into the next services to change his underwear) I always just hope for the best now if I deem it past point of no return. It’s not a very well thought out system in my opinion and I think people have to pay so much attention to their speedometers and watching the gantries for sudden changes its taking their concentration away from the road and traffic around them.
When they’re showing 60, there may or may not be a problem ahead.
When they’re showing 50, queue a few miles ahead.
When they’re showing 40, if you’re not already stationary, you will be soon.
When they’re showing 30, you are stationary, might as well put it on break as you won’t be moving much in the next hour or so.