As a resident of Hamburg I can assure you it will not become a car-free city within the next 20 years. So far, we don't even have an "Umweltzone" (green or environmental friendly zone) where only cars maintaining certain filtering and mileage standards are allowed to drive.
See their official statement (in German): http://www.hamburg.de/pressearchiv-fhh/4257482/2014-01-24-bs...