Google Maps and Gasoline

Can Google Maps help you conserve gasoline?

Let's say you are planning to drive on an extended trip-- perhaps from Washington, DC to Montreal, Canada, for example. You might go to Google Maps to get your travel directions.
In addition to the various roads and turns to make, Google Maps provides you with the approximate distance (610 miles) and estimated duration (10 hours) of the trip.

Although Google doesn't show you multiple routes to your destination, per se-- you can "grab" the path and adjust it to avoid certain roads. If you kept an eye on the time (first and foremost) and the distance (secondary, I should think), that'd give you enough raw data to determine which route should use less gas.

If someone wanted to get really sharp about it, they'd create some Google Maps mashup with one of those Gas Buddy type web sites-- and then integrate the method above so as to take you through destinations with the cheapest gasoline prices.

And, if I thought of it-- odds are someone else thought of it before I did. Someone smarter and with bigger web programming chops. This might already exist out there somewhere-- it's just a matter of finding it.