Comment by Terr_

you're basically removing a dam - resulting in far more stress on the rest of the system.

Adding to the grab-bag of useful flow-dysfunction concepts and metaphors: Braess's paradox. [0]

Sometimes adding a new route makes congestion strictly worse! Not (just) because of practical issues like intersections, but because it changes the core game-theory between competing drivers choosing routes.

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