"There are actually special satnavs for trucks that know all about restrictions."
I'm not sure how effective they are.
Most if not all the routing websites seem to know that the junction at the bottom of my road is too sharp a right turn for an HVG so will advise me to turn left and then turn back to avoid that. Because they don't ask what sort of vehicle I'm in I assume that they're taking restrictions into account when they know about the,
But the same websites have traffic cross over the route I'd normally drive out to to pick up the motorway and direct them down a twisty set of lanes from which the larger vehicles have had to be rescued. So I'd guess in that case that the navigational databases are sharing data which doesn't mark this as a bad route for HGVs.