That's what trains were, in 1825.
Today, no matter how badly politicians may wish otherwise, they're not. In Portland, where light rail "trains" are all the rage among the political set, they're not even effective as mass transit solutions, due to the shortsighted decision of those same politicians to run the "trains" through downtown - which boasts extremely small "city blocks". So small, in fact, that light rail "trains" here can never consist of more than two cars.
And while it would have made sense to allow for possible expansion to three, four, or more cars as has been done elsewhere, Portland ensured that not only can that not happen, but they can't even add more two-car "trains"; they've simply designed too many bottlenecks into their multi-billion-dollar "system". Oh, it's colorful and shiny - for now - but it would have been wiser to "invest" in buses and roads. Unlike their "trains", you can actually run multiple buses at the same time if needed, and they also offer a degree of flexibility that their funky rail counterparts lack.
Because if a bus were to happen to, say, run into a police car, other buses aren't delayed as a result. Oh, yeah - that's just common sense.
And in Portland, you can have any kind of sense you want, as long as it isn't "common".