We call large trailers with heavy loads slug catchers, they travel that slowly, that only slugs get squashed under their wheels
Heavy loads can cause all kinds of problems, we had one on the A180 a long time ago now when the driver realized he wasn't going to fit under a bridge. So somebody I know had to go out let the tyres down on the truck and trailer just enough to let the load pass under the bridge, then re-inflate them all the other side.
There was over 30 tyres on it, it took half a day.