I don't think gas prices are high enough yet. SUV's and big PU trucks are still big sellers. Every time I go to the PO there is someone in a big gas guzzler, leaves engine running while they go in and get their mail, comes back and reads mail in vehicle with engine still running... (and this is in moderate temps so it's not for heating or cooling)
If I was in charge I would add taxes on until it was $10 a gallon, use the extra money to fund alternative energy (domestic) and a subsidy for low-income drivers. Then see if they still want to keep the engine idling.