Even with maximum speed, the bus will take the same amount of time. That month only passes faster for you.
You have to compromise there in some way. If it were real time (or closer to real time), you would have two options:
The game time passes incredibly slow. It’d take ages to even reach the year 1900.
Or, the vehicles would run incredibly fast. Let’s say that your bus would, in reality, take one hour to complete its route. On slow speed, the game takes only seconds for one day. Your bus would have to run fast enough to complete the whole route 24 times in about two seconds.
Maybe take the individual bus or train as a symbol, or an abstraction. It’s not really an individual bus but a game representation of the buses running that line during a few months. Or something like that.
That’s a compromise all these games have to make, not only transport simulations. In Civilization, it can take you hundreds of years to move an army from A to B. On the plus side, you don’t have to actually play for 6000 years, which would be quite difficult. 😉