It probably has nothing to do with Google redirecting traffic up poorly maintained mountain roads during a blizzard in California last month (previously), but TomTom has posted a piece explaining how its algorithms avoid sending drivers down potentially dangerous routes in Finland even though, on paper, they’re shorter.
TomTom’s routing and location technology recognizes that the shorter route to Koli National Park is on winding unpaved roads, made up of sand and gravel, and it takes that into consideration when computing a route for a driver. It places significant importance on this information. […] Even though the unpaved route is shorter, it’s still not considered “better” than the longer paved route when all things are considered. If map data didn’t include this contextual data about the specific road, the unpaved road would most likely be the default route suggestion.