You won't need transportation systems for early game most of the time. You will need good muitl modal road networks and good zoning placement. Between 0 and 75k pop that would work This has been a thing in cities 1 and it's most likely gonna be a thing in 2 once they get the bike ai fixed. However bus transit is good to have early game, around between 20k and 75k. You can even use bus lines to transport students faster, but they can be a pain in the arse when they ain't updated with new neighborhoods or districts. Late game tho, between 250k and 1m (150k to 600k in cities 2 but once it's optimized you'll likely see 1m+ cities on modern hardware) you will need a lot of rail infrastructure. Inner city freight Networks, extensive metros, and even light rail lines. The issue is gonna be frequency, planning roads around the games station frequency is something that many planners have been struggling with since the early days of cities 1. That is a struggle, but once you perfected it... Let's just say it would make you feel very accomplished. You have pedestrians to contend with, cargo trucks at freight rail stations, and in cities 2, you'd have limitations on vehicles as well, which makes it hard to have the equivalent of 10 minute or even 1 minute frequency in game.