According to some data I collected, you can make ~2300 bells/min diving, which means 500k would take a little less than 4 hours.

https://docs.google.com/spreadsheets/d/12psfVrErw9okyAP8Dr9DX7-B7wuh6g5E1Vq3g-H65_I/edit?usp=drivesdk

There is research showing that adding lanes only helps for maybe six months. Then people realize that the route is better and change the routes they take, which leads to more congestion again. Fewer lanes can actually decrease congestion.

https://smv.org/learn/blog/how-does-roadway-expansion-cause-more-traffic/

This post covers it pretty well https://phauer.com/2015/checked-exceptions-are-evil/

Darmok and Jalad at Tanagra