This just launched... Not applicable to Montana just yet... Thank goodness!
http://www.trulia.com/local/#commute/detroit-mi
Trulia Builds HeatMap for Commuting
So, launching today [June 22] is Trulia’s first iteration of the Commute Map, a way to visualize driving and public transit times. With this new product, we aim to give Trulia users a better understanding of commute times to work or anywhere important, to help them find the best place to live.
Here's what Trulia did to build it:
We’ve taken the base data, OpenStreetMaps and General Transit Feed Specification (GTFS) feeds, and produced a visual representation of commute times. We allow users to specify a start point, and then calculate estimates that can be manipulated with a simple slider. With nationwide coverage across millions of transit data points, we’ve built an interactive and responsive map that overlays highly detailed transit results for any local query.
