Smart Motorways were a Tory government idea designed to be "car friendly" and increase apparent road capacity without actually costing much money -- by using already-existing lightable signs above the motorway to convert the hard shoulder into another lane of traffic, and adding in "refuge areas" every $[$RANDOM % 5+1] miles.
The trouble is, if you're in a motorway where every one of the now four lanes of traffic is going at the speed limit of 70 miles an hour (or, more likely, 80 miles an hour) and your tire explodes, you might not be able to coast the requisite distance to a refuge area, and you might not have the wherewithall to adequately pull into what is in effect a small siding about the size of an articulated lorry. If you break down in a "live lane" the signs are supposed to change to move traffic out behind you, so it doesn't ram into the car.
Naturally, this hasn't worked well, and a bunch of people have died. At least one coroner has specifically called out Her Majesty's Government for directly contributing to deaths and blamed the smart motorway concept in general. There's at least one harrowing 999 call I've heard somewhere of someone saying "Help, I've broken down in lane 2 of the M4 and my car has stopped and I couldn't get into lane 1 when <BANG> <sound of young child crying> <no more adult voice>".
Some of the "smarts" in smart motorways in doing lane-light switching this have been provided by humans and/or computer vision on the basis of CCTV. The trouble is, they've been ineffective. This announcement states that they're going to replace the previous approach with mmWave radar that I presume can detect changes more rapidly (quite how that works with shadows and reflections -- and cars in front of lorries, I don't know).
Fundamentally, this seems to be "papering over the cracks" of the idea -- and I unfortunately don't think it will work. Many, if not most, British people want to go back to the old system of having 3 lanes + a hard shoulder. We don't understand why the Tories really, really love smart motorways: it probably comes out of a combination of 'driver friendly' Manifesto promises combined with economic modelling about the cost of traffic jams.