San Francisco just rolled out its SFPark system in eight pilot neighborhoods. SFPark uses sensors in parking spots to detect when they’re occupied. Using the SFPark website or iPhone app, citizens can see where there are free spaces, and how much they’ll cost, right now. Then, beginning this summer, the city will actually start changing the price of parking spaces based on demand. Rates will change as often as once a month, dropping to as little as $.25 per hour in places where demand is low and rising to as much as $6.00 per hour on the most congested city blocks.