Sounds like a good idea in theory but in many places in the US when you get off the highway you get a major drop off in the quality of roads and availability of

Sounds like a good idea in theory but in many places in the US when you get off the highway you get a major drop off in the quality of roads and availability of food/gas. If you really care about reducing your CO2 the best option is significantly reducing your travel not slightly optimizing you routes.