QDU is not an airport code in the usual sense - it identifies Dusseldorf Hauptbahnhof, the city's main railway station, used by airlines and rail operators for through-ticketing between trains and connecting flights elsewhere in Germany rather than any airport of its own. Travelers landing on a QDU segment are actually arriving by train into central Dusseldorf, Germany, and the honest starting point for a rental car is the station itself or the true airport nearby, not a terminal building that does not exist under this code.
Dusseldorf Hauptbahnhof sits right in the city center, one of Germany's busiest rail hubs, with high-speed ICE trains connecting onward to Cologne, Frankfurt, Hamburg and Berlin, and car rental counters from international and local operators a short walk from the main station hall, making it a genuinely convenient pickup point for exploring the city and the wider Rhineland. Dusseldorf Airport (DUS), the real regional airport, lies only about fifteen minutes away by S-Bahn train or taxi and has its own on-airport rental desks, so travelers flying rather than training in often find it just as practical to collect a car there instead, particularly if their itinerary continues beyond the immediate Rhine-Ruhr region.
Driving is on the right throughout Germany, and the autobahns radiating from Dusseldorf, including the A3, A44 and A52, are fast, well-maintained routes that carry no toll for passenger cars, unlike some neighboring countries such as Switzerland or Austria. City traffic around the Hauptbahnhof and the wider Rhine-Ruhr conurbation, one of Europe's most densely populated regions, can be dense during weekday rush hours, so many drivers wait until they are clear of the city before settling into the open autobahn network. Fuel stations are plentiful throughout the region, and winter driving occasionally brings snow or ice, though conditions are generally milder than in eastern or alpine parts of the country.