[jdawg77]

Can't up-vote this one enough; worked at a startup for a while tackling all sorts of traffic related stuff with proprietary IP, industry veterans & more. Suffice to say that there are tons of papers out there which clearly say taking N% of the number of cars off the road reduces congestion by Y% - a very much larger impact than the number of cars taken off.

This is because traffic, in general, is really caused by a small number of cars. It seems like it's everywhere but the root cause (there was a paper even on HN that talked about it) is that people can't follow each other at an even speed. This uneven speed then results in more braking, more backup, etc. A few cars in the lead who don't accelerate properly can have a disproportionately negative impact on traffic flow and average speed.

[jordanthoms]

It's the same problem with queues - the people at the front don't have as much incentive to move quickly, since they're already at the front of the queue.

Probably the only way to really solve it is autonomous cars.