[Mercat]

Can some auto expert figure out the cost of running the engine without the cost of the gas and factor that into the equation? In other words, if it takes an hour longer to get to ones destination, just running the vehicle that extra hour has what cost?

[Gondring]

What Car? magazine:
The average car consumes 38 per cent more fuel at 70mph than it does over the same distance at 50mph. At 60mph it uses 34 per cent more than at 40mph. [And at 100 mph, you use 5 times as much as fuel as at 50 mph!]

What other costs are you thinking of, regarding "running a car longer"? I think the costs for the trip actually increase, too, as the wear on the car is greater for a shorter trip at high speed than long trip at low speed, barring exceptional cases.