On an earlier post on this mastery item, the poster said they got the speed up to 70 then escaped out so they could return to run the scenario without the penalty.
You are mixing 2 different things here: The Steam achievement: CL314: To the Max Reach a speed of 70mph in the Class 314 The Mastery (DTG Live): Requires you to reach 80mph and finish the service / scenario.
The thing is, it's entirely possible to run it up past 70, finish the service, and still get gold. Commuter trains get so many points opportunities (1000 pts per station, basically), that missing out on one 30-pt "driving under speed limit" score makes no difference. It's easiest with a Neilston-GC service, since you have a long run out of Neilston before you have to stop again.
There is a small part neat Shields Depot were the limit is 70 or 75, but you arrivé at a slow speed so you never reach that speed before the next speed limit
What does racing along at 70 or 80 mph on a suburban commuter line where most stations are less than a mile apart have to do with simulating a real world railway? Is there something about TSW2 that I'm not getting? Perhaps it belongs in an arcade along with the racing and pinball machines.
What indeed? If these "achievements" are what constitutes "Mastery", then it's worthless. Like chasing meaningless points and medals in pursuit of imaginary prizes. Just my take. Glad it's possible to ignore the more childish aspects of the game.