Getting around Hanover by public transit is fast and easy. The transit system of buses and tram/U-Bahn lines (so-called Stadtbahn or ‘city rail’ because some are trams on lines underground) is run by Üstra. Board most U-Bahn lines, including U-Bahn 8 to the Messe (fairgrounds; €2.70, 19 minutes) from inside the Hauptbahnhof; all of the lines meet up at the main central U-Bahn station, Kröpcke.
U-Bahn lines 10 and 17 are the exception. These are overground trams leaving from behind the Hauptbahnhof, right near the ZOB main bus station, and they don't run to Kröpcke. (The late-night service of the 10 does, however, and starts from inside the station.)
Most visitors only travel in the central ‘Cardzone Hannover 1’ zone, where single tickets are €2.70 and good-value day passes cost €5.40. If you wish to travel in zones two/three, single tickets cost €3.50/4.40, while day passes cost €7/8.60.
Call 0511-8484 or 0511-3811, or try www.bettertaxi.de/en. From the centre to the fairgrounds, a taxi costs about €35 to €40; to the airport it’s about €30 to €35.