What gets me is the advance speed markers can suddenly drop from a high speed to very low and sometimes it is panic stations trying to slow down, I have even stopped the train then had to start again which I know is terrible driving, good job it isn't for real.
I tend to travel at a comfortable speed and not try to keep the the speed limit because of this, I usually end up late at the finish of the scenario, I know if I play the scenario more often or I travel that route I would get to know the slow down points but if it is a new route it can be a bit hectic.