Commercial and passenger service vehicles are fitted with Tachographs, and although they are not as fancy as OTMR, they can be used to see if a professional driver is driving within the rules, including speed, meal breaks, sleep breaks. If a driver's route is known, then the speed along a given part of the route can be accurately shown (they are a calibrated instrument).
These devices are now not the old fashioned piece of paper in the back of the tacho head, but instead are digital and use a smart card.
Commercial and Passenger service vehicles are also speed limited (commercial class 2 and class 1 are limited to a maximum of 90 km/h (56 MPH) and Passenger service vehicles are limited to a maximum of 100 km/h (62 MPH)
In other words, tachographs now are good enough to act as a deterrent to speeding and the RSL should make it impossible on NSL dual carriageways.