Sometimes I want to take the fastest route possible, but most times I want to take the cheapest route. By cheapest route, I mean one that includes a cost for my time as well as fuel, depreciation, and tolls.

I live in a part of Austin where the fastest route is often a highway that goes the long way around, but there is a slightly slower route that is direct. I'm willing to take 2 more minutes to drive if it saves 7 miles on my car. The US govt. puts the price of a mile on a car at $0.70 (US Dollars) and, as an economist, I think that's about right. 7 miles saves me about $4.90 and that's worth more than 2 minutes of my time.

You can advertise this as good for the climate too. I'd drive fewer miles.