Smart motorways, or any other smart road system, will always have to contend with drivers who are a long way from being conscious, let alone smart. This is probably why governments are so excited about automated cars, as it removes the dumbest part of the whole sytem.
The ones I hate are 4 or even five lanes. The number of people making silly moves because they are in the wrong lane get added to the few who breakdown.
On the other hand, feeling unsafe makes folks drive more carefully. Tests were done many years ago (Swindon I believe) where the kerbs were removed and cars had to get along with pedestrians. (1) the accident rate dropped and (2) the traffic dropped because nobody wanted the hassle of people in the road and everyone was being much more careful. It's not continued because local councils have huge departments devoted to street furniture, traffic lights and all the traffic management BS our towns are infested with.
There's a junction in Swindon that used to be controlled by traffic signals, where a one-way system forks. It all worked reasonably well, although there was always the possibility of pedestrains crossing against their lights. The took away all the lights, and the kerbs, making it all one level, with no indication of priority. The added block paving to the 'crossing points', like a lot of raised traffic calming measures (which are not pedestrian crossings). Now no-one knows who has priority, everybody tries to bully and push, cars and pedestrians, and it is just a worrying mess.
The local council deem it a success, because what little traffic congestion there was, has significantly reduced. This is because far fewer people use it, choosing instead to take alternative routes. Where traffic used to be nicely spread over all available routes, and flowed acceptably most of the time, rarely becoming gridlocked, it is now 'busy' on all the other routes (in normal times) and becomes difficult at peak times. That'll be a success then.
There are also two roads that have been made into 'Home Zones'. This is where kerbs are removed and everyone shares the space. Speed limit is 20, although difficult to achieve, and was unusual to achieve before the change. There are some brightly coloured traffic calming posts, and a tortuous path through. There is a small primary school, with these two roads one each side, so the reason makes sense, but the streets are narrow, with terraced houses. Parking was difficult before, and the new layout removed about two-thirds of the spaces. It is rare to see pedestrians in these areas, except at school in/out times, when traffic was slower anyway. A lot of money spent with no noticeable benefit. Pedestrian casualty rates here before the change was zero I believe, so difficult to improve on that.
(Not far from the 'red light' road, which contains speed humps. Makes me smile every time as I drive over the bumps, slowly of course.)
Swindon is better in other areas. The Magic Roundabout actually works well, for the locals. First encoounter can be frightening, but once known, it works very well, and keeps flowing even at the worst peak times.
On West Swindon, when developed, an experiment was tried, where each portion of the estate was joined by footbridges and underpasses, with the main arterial roads having no pedestrian access. All bridges and underpasses are at ground level, no steps or slopes, as the main roads do the rising and dropping to accommodate. This removes reluctance to use bridges, and makes underpasses less scary, and unlikely to be used by homeless, or others. This all works well. Traffic in the estates is slow, as there are no short cuts, so no benefit of being in there unless you live there or are visiting. The main roads rarely see pedestrians, so flow at 40mph well. Compared with similar developments with pedestrian access to the main roads, the pedestrian collision rate is nearly zero. A great success, strangely not copied widely.
