The driver-less Sky Train operates 23 meters (75 feet) above the ground. It connects the airport terminals and Parking 4/ 5 with the new ICE. rail station on the heavily frequented Düsseldorf-Duisburg railway line in a four-minute cycle. The ride over the 2.5 kilometers (1.6 miles) long track takes approximately 5 minutes. The system is now operating well and was finally accepted by the airport authorities in December 2006, after extensive improvements.