You know what'd really reach almost a Milgramesque level of messing with people's minds? Make all cars display instantaneous cost, based on computed gas mileage (from fuel flow and speed) with the data automatically updated by having the computer talk by Bluetooth to transponders on gas-station signs.
Somewhat less flippantly, a mileage display could maintain historical data for the car and show a curve of mileage vs. speed, so you could decide for yourself what's a good tradeoff among schedule, cost, and the need to keep up with traffic. We should be able to *know* rather than guess when a particular car is past its engine's optimum and-or running into an aerodynamic wall (and seeing how this varies with elevation). The historicals could even be used to some extent as a maintenance indicator and-or an alert to changes in driving habits or a guide to selecting the most cost-effective brand of gas for your car or...
Actually such a display is so useful from a variety of standpoints that I'm surprised more cars aren't capable of it. Knowing your best economy cruise (through measurement, rather than with the SWAG that there's a broad optimum somewhere in the 40-55 mph range) can be a big deal when trying to save money, help collectively cope with an energy supply problem... or deciding whether to turn back or nurse the remains of your tank to the next town.
--Joe
