Can you imagine how much traffic there would be if NYC didn't have the MTA? The principle of induced demand tells us that as long as there are roads they will have roughly constant traffic because people are willing to spend some roughly constant amount of time getting to and from destinations by road each day. More roads speeds up everyone's commute which brings in more drivers, which brings traffic right back to the baseline terribleness.

The question is how shitty it would be if they also had everyone on them who's currently on public transit.

So basically, it is a traffic-free panacea for everyone who chooses to use it. It's not a goal of trains to eliminate traffic for everyone who insists on driving.

https://www.tomtom.com/newsroom/explainers-and-insights/indu...

The induced demand argument works for trains too. If NYC didn't have MTA (no subway, no LIRR, no MNR) then the population of NYC would probably be 1% of what it currently is. Building more train tracks and having better train services also encourages more people to move to NYC so that these new train services become more utilized.

Neither roads or train tracks solve the traffic problem.

The tubes were shut down due to a transit workers strike recently in London. Here's what the streets looked like:

https://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2F2...

Now imagine if all those commuters were in cars.

Yep, this is a good point. There are appropriate technologies for each situation. It's not a winner-takes-all contest.

For another example, can you imagine trains replacing school buses in a large, rural school district? Sometimes (not always), buses are better than trains.

Any one part would have the about same amount of traffic it does now. It would just sprawl out bigger across adjacent counties and the highest density parts would be lower density.

See also: LA