When you click the the “Avoid Highways” checkbox, the route instantly updates to one that tries very hard to stay off of interstates, motorways, and other major roadways. This may give you a much longer path, but one that you may find more suitable. If it isn’t what you want, you can uncheck the box and quickly revert to the normal route to help plan your trip.
A good example of such a route can be found here, from Seattle to Google’s office in Kirkland. The route skips the I-90 and WA-520 floating bridges across Lake Washington, taking the scenic route around the lake through Juanita instead.
This is a handy feature. There are many times I know that the highway is backed up and i want to take the backroads.
Google really needs a routing API. Right now Virtual Earth is the only team that has a routing API freely available to developers. The problem is every set of directions shown costs money. Microsoft has their own routing engine so they can do it without accruing major costs. Yahoo! does as well, I expect that they will soon offer a routing API. I can’t believe that Google isn’t also making plans in this area.
Updated: In the comments Ian lets me know that I was wrong about the exclusivity of the feature. Mapquest has had this for years — just as they’ve had their own routing engine for years.
MapQuest has had an “Avoid Highways” feature in addition to a “Avoid Tolls” and “Avoid Seasonally-Closed Roads” feature for many years. (Go to http://www.mapquest.com and click on the “Advanced Options” link in the directions section of the page.)