Stuttgart is the first airport in Germany to plan the use of self-driving vehicles. The airport will begin with jet sweepers for winter maintenance and baggage tractors. Together with the vehicle manufacturers Aebi Schmidt and Volk, the first fully automated prototypes are scheduled to be developed by 2022. After that, the self-driving vehicles will be tested in real conditions on the runways, aprons and taxiways.
More information in German (source): http://www.airliners.de/selbstfahrende-vorfeldfahrzeuge-flughafen-stuttgart/50747