Get a "Like" from "Uncle Sam"
My idea is for traffic reduction, rather than traffic Management thru high tech data manipulation.
What are the main groups of "travelers" on the roads today?
For category 2, I propose giving tax credits to corporations that will empower their employees to work off -site half the time. This will become especially important as our population continues to increase and continues to age.
Ensure that the wisdom and experience of older workers is not scrapped in favor of continual youthful experiments.
While it may be true that PEOPLE dont respond well to purely financial incentives, corporations do! Tax breaks that encourage job reform is a way for our pathetically bloated governments to do something useful :).
For categories 1, 3 and 4, I propose a system of Pollution Credits that can be bought and sold on the open market. This has utility beyond just traffic reduction, but let's just consider traffic right now. Everyone adult of driving age gets the same number of credits. You can spend them any way you wish. Most people will apply them to gasoline purchases. Want to drive an SUV or a 1960s Muscle Car? Fine, you'll run out of credits many miles sooner and simply drive less. Or, you will buy more credits from a poor student or burger flipper or janitor who doesn't own a car at all. Win, win! There will be an additional incentive to be car-less beyond just ideological righteousness. Want to throw your credits into a carpool situation? Good idea... you'll still get to work, but have extra credits to sell.
Super cheap, embedded system gadget that you stick to every dashboard. Feeds current speed/direction without needing to have a cell phone. Works from all cars/trucks old and new.
...And my hands down favorite: Time Turner. Turn time back to lightest traffic, and drive to work. Turn time back up to when you are supposed to be there! Perfect.