Has this person every y’know looked out the window while riding on a Caltrain? The cost alone to acquire the properties adjacent to the tracks would be astronomical
You do realize that this is talking about only using the current two-track rail geometry and not about ballooning the size of the track to that of a large highway?
Presumably, this could all be done without extending the footprint of the rails already present just by increasing the number of trains, cars per train, speed of the trains, or improving the design of the cars. Really, the beauty of public transportation is that you can get much higher density (and speed) than individual transportation if done correctly.