[Nullabillity]

If congestion stayed the same then ~1.5x (slightly less in reality, since each lane does introduce some overhead) the people were able to get to where they wanted (still a win!) or there was a bottleneck somewhere else in the system (so go address that as well!).

[distances]

Interestingly by Braess's paradox adding more lanes can increase congestion, and removing lanes can speed up the traffic.

https://en.wikipedia.org/wiki/Braess%27s_paradox

[ohgodplsno]

No, merely that other transit systems have been abandoned in favor of your car lanes, which makes them an even worse option. We always scale usage relative to what is available, whether that is highway lanes or energy use.