This exists - for bikes. For a few years now, Cyclestreets have been offering 'fast' vs 'quiet' routing (quiet being the stress-free option on a bike) http://w

This exists - for bikes. For a few years now, Cyclestreets have been offering 'fast' vs 'quiet' routing (quiet being the stress-free option on a bike) http://www.cyclestreets.net/journey/ http://www.cyclestreets.net/journey/ It tries, but often it will warn you that some parts of the route have to take in busy roads. They do it as an API (http://www.cyclestreets.net/api/ http://www.cyclestreets.net/api/), it's used in a number of apps and sites, and most of it is open source (https://github.com/cyclestreets https://github.com/cyclestreets). I'm sure you could similarly construct stress-free driving routes, you just need a metric and the data?