Active Traffic Management
I've driven the M42 a few times in the last month, at fairly peak times and have never been held up there, it's a bit weird seeing vehicles on the hard shoulder for the first time!
What I noticed was the hard shoulder was mostly used for people taking the next exit only so it wasn't heavy with traffic, and I suspect can quickly be taken out of use in the event of a broken down vehicle.
The only thing that did annoy me was on my most recent trip, a Sunday evening, the signs kept switching between 50mph and 60mph pretty much every gantry which was annoying to keep on top of (and you don't get much choice with Gatso's behind most of them!!)
I certainly prefer this to the stop-start-stop-start you frequently find yourself in on the M6, driving at a constant 50mph is much less taxing than having to keep changing gear as the speed varies between 0-50mph for miles and miles.
Overtaking lorries can be a big problem, as as soon as one indicates to pull into the middle lane a lot of people automatically move into the outside lane and everything beings choking up. Having been in Germany, Holland and Belgium last year it's noticeable that is is banned, usually from 7am - 7pm or similar and HGV's keep to the outside lane.
They've been trialling this on the A14 with plenty of signage but every time I've been down there very few large vehicles pay attention to it and carry on with their overtaking as normal.
The other thing I've noticed causing problems is people joining a busy motorway, people will often try and move over or slow down to allow new vehicles to join the motorway but again this can choke the traffic up...perhaps we could use the hard shoulder here, allow joining vehicles to use it for a mile or so allowing them to speed match and join a gap in the motorway, safer and with less impact on the other traffic?
Feel free to correct me on anything, I've only been driving alone for a year but have clocked up 8,000 miles with lots of motorways so I think they are fair observations :)