> I would be interested to see how the use of lots of small street routes around a main route affects the flow of the main route, and what the efficiency gain generally is.

I wouldn't assume there's an overall efficiency gain. That's part of the problem: in many cases, a shortcut that would work if a few cars used it causes problems (jammed intersections, etc.) if too many cars try to take advantage.

Someone who knows graph theory more than I do could comment, but more generally I don't think there's any guarantee that a situation where every vehicle uses a greedy algorithm will result in overall greatest efficiency. I could swear there was an article on this within the last year but I cannot find it.

> Maybe it is also in your best interests if the street is modified to accommodate modern use cases.

At least in the UK, in a lot of cases that's just not feasible. Take the image I posted above for instance: http://c8.alamy.com/comp/DXHF2G/terraced-street-in-hillsboro...

The only ways to widen the road would be A) prohibit parking -> now residents have nowhere to park, or B) start demolishing houses.

You're under the impression the government does that sort of thing in the us (modify roads to address demand). In my experience that is largely an artifact of history now.

You can't widen a residential street without eminent-domaining everyone's front garden and/or maybe demolishing some of the houses.

Tree lawns are quite often property of the municipality. If they're big enough, they can be sacrificed without the residents having much recourse.