The advantage of busses and bikes are that they can use the same roads we already built for cars. We don't need to build new infrastructure to make busses and bikes much better, we just need to limit car access. That can be done by significantly lowering speed limits for private vehicles, tolling a lot more roads and streets, and in cases where we can (especially in cities) ban personal vehicles entirely.

Trains need infrastructure, but a lot of the train infrastructure is already there, it just needs to be repaired and modernized. The USA freight network is one of the most comprehensive train networks in the world. The problem is that is has gone through decades of neglect, and trains are required to crawl through a large portion of the network so as to not derail. Urgent modernization of the rail network could happen in years instead of decades.