In addition to all the excellently thought out and presented ideas already extant, here is one more, although one of minor but measureable importance. When we are stopped, as when chatting with a nosey policeman, or, at a red light, our automatic transmission, if left in gear, will drag down the motor idle speed a hundred RPM or something like that. LOWER MOTOR SPEED MEANS LESS GAS USED! Alternatively, our manual transmission, unless we are doing something really weird with our clutch, will allow motor to run at its usual higher RPM. HIGHER MOTOR SPEED MEANS MORE GAS USED!
