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Comment by unreal37 | Hacker News Reader

Do trains cause traffic congestion? Like if there were 10 more trains passing through downtown Detroit per day, would it add minutes to the commute of cars due to train track crossings having to stop traffic more?

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Trains cause traffic congestion on the train tracks. Trains already stop each other, to take turns on tracks when there are single tracks going through an area with more than one train. Trains have entire dispatch offices to manage where each train is, how long their operators have been working, and have to fit very tight regulations, sometimes even stopping trains to switch people out when their regulated working time is maxxed out.

For the most part, this all works smoothly. But the idea that you can just throw more trains on the tracks without impacting even their own traffic isn't seeing the big picture.

I'm unsure about the Detriot specific case (it might have an unusual number of road crossings on very high traffic streets) but I'd suspect it would reduce congestion by taking cars off the road. Most commuter trains have this effect.

They're not necessarily taking cars off the SAME roads though (think arterial highways vs surface streets).

There's also Braess' Paradox to be aware of, which means that reducing congestion can actually INCREASE congestion. https://brilliant.org/wiki/braess-paradox/

I think you misunderstand Brasess' Paradox. It is when adding to a system decreases the efficiency of the system by adjusting the Nash equilibrium to be further from the optimal system wide solution. "Reducing congestion increases congestion" is a not a logical statement.

My comment left the possibility of Brasess' Paradox open in the specific Detroit case, but practically speaking commuter trains are used by most major cities worldwide as part of a comprehensive transportation system. For many cities rail is among the most efficient subsystems of their transportation system.

This is a significant reason why subways exist even though tunneling is significantly more expensive than just clearing and laying rail tracks.

Same-level railways crossings are increasingly rare in Netherland. It's safer and less disruptive to have trains elevated a level above the car traffic. Tunnels are only useful when they have to go through extreme dense areas where there's no room for rails above ground, like in city centers.

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