Busses can connect Train Stations from Martian Express and transport colonists between them. They are slower than trains but don't need tracks and for that they can connect stations at different terrain elevations.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2865239764

This is an "proof of concept" version so let me know what you think of this approach to overcome the limitation of trains and ramps which I know is the major complain.

You can build Busses like the other RC vehicles but no tech required (for now) and using the infopanel button connect two train stations. In the future I may try to add a Bus Station building too and allow connect those with bus routes (or routes between bus stations and train stations)

Martian Express DLC/CCP is obviously required and if "Martian Express - Enhanced Passenger Transportation" mod is enabled colonists can use bus + train to reach their destination (only switch at large stations for now)