Common sense wrote:
How can you nip people for going 5mph over the limit on a clear stretch of road, yet allow slow moving walls of steel on a motorway?
I mean you also get the other problems of the sheer backlog of traffic they cause when they are on a motorway at rush hour.
But the crash didn't happen on a motorway. It happened on an all-purpose dual-carriageway.
All road users are allowed on an all-purpose dual carriageway - pedestrians, cyclists, horse riders, invalid carriages, mopeds, learner drivers, tractors, JCBs, etc.
A motorway is a "special road", and all of the above classes of vehicles that I've mentioned are prohibited from using them (except HGV learners).
It's a sad fact that the Government believe that the word "motorway" is to be avoided at all costs if it's building a new road. The planned A14 upgrade (despite being in the top 10 busiest of all of the UKs major roads) won't be built as a motorway, but as an all-purpose dual-carriageway. It won't even be built with a hard-shoulder.
We have a few A-roads which have largely grade-separated junctions (i.e. motorway style junctions) - yet are still A-roads and not motorways. Most do not have any restrictions on use. There has recently been a couple of accidents on the A34 when vehicles crashed with a tractor. One of the incidents involved a coach and a tractor being used to transport something from Winchester to Oxford (i.e. virtually the entire length of the grade-separated A34) every day.
I personally think that new roads designed to form major trunk roads which are planned as dual-carriageways should be built as motorways, or given special-road orders (like the A55 at Conwy of the A1 and A720 near Edinburgh - which although aren't motorways, they still have restrictions on who can use it similar to that of motorways.)