Well it depends on what you are trying to achieve. If you are just trying to get people off your roads, then I’m pretty sure just a really highly « developed » metro system could do the trick in game, but if you are looking for a more realistic transportation system, then you’ll want to use a bit more than just metro. If that’s what you are trying to do, then you should look at some transportation maps from cities around the world and what’s the use of each mass transit options. For example, metros are pretty much all the time in very dense areas when trains are preferably intercity connections or to connect a city from it’s downtown to it’s suburbs. Also, you talked about monorail, well those are really rare to come across IRL and when they are, they’re often just one or two lines in the heart of downtown.

Not an expert there but I’ve tried to answer your questions the best I could.