Dartford Crossing "Safer" in what way exactly?

A press release from the Highways Agency issued today about "improved safety measures" at the Datford Crossing reaches me. It starts:

"Road users are set to benefit from improved safety measures on both the north and southbound approaches to the Dartford River Crossing.

"From tomorrow (27 June) drivers will see signs reminding them that the speed limit on the Queen Elizabeth II Bridge clockwise carriageway between the A282/M25 junction 31 and the plaza, and on the anti-clockwise carriageway between the M25 junction 2 and junction 1a, is both mandatory and enforceable."

There are, and always have been speed limits on approaching the Dartford Crossing. There are big signs that tell you about them. Presumably, every driver knows that a speed limit is mandatory. They run a test to check that before you can drive, and everything.

So why does it make life safer for road users to remind them not only of the speed limit on approach to the crossing, but also remind them that they really should obey that speed limit? Just asking...