Cars don't get in the way of the heavy rail trains, and the trains don't get in the way of the cars, either. But heavy rail is expensive. Monorails have never gotten very popular, although some people think they should be. If you'd like to ride a monorail, ask your parents to take you to Seattle. Not all passenger trains are built to carry people inside a city.
Some passenger trains carry people much longer distances.
Amtrak is the name for the national railroad system. If you want to go from San Francisco to Los Angeles, but don't want to fly, you can take an Amtrak train. Amtrak trains run all over the United States. They're nice inside, like commuter trains. In Europe and Japan, some special trains have been built to carry people much faster than other trains can go.