Roads already occupy massive fractions of most cities. Making cars drive closer together or collaborate will make roads environments more hostile to pedestrians

Roads already occupy massive fractions of most cities. Making cars drive closer together or collaborate will make roads environments more hostile to pedestrians than they already are - and arguably in many places we shouldn't even really have private drivers aside from business users on the roads, given the massively disproportionate space they require vs a pedestrian or PT vehicle. A train line has 10x the capacity of a single lane of road. Even if trains are only coming every few minutes, its impossible to compete with a train carrying 1k people with cars. Perhaps reasonably loaded busses would be comparable or better, but that's not the argument you're making. Trains are financially efficient because of cost of energy and drivers (and, arguably, roads + cars move much of the expense to the public, where as everything related to the train is on the operator's balance sheet), but they are also very space efficient, compared to roads + cars.