Bremen's low-emission zone came into effect in January 2009. Only cars displaying the green discs are permitted to travel in the districts of Altstadt and Östliche Vorstadt, some parts of Schwachhausen and most of Neustadt. If you are staying in accommodation within the low-emission zone, you can drive in this area for the duration of your stay without having to display a disc. Instead, you must display a booking confirmation that is clearly visible though the front windscreen and that indicates where you are staying and how long for. This does not apply if you are staying in accommodation outside the low-emission zone. If this is the case, you will need a green disc or special dispensation to drive your vehicle in this area. The Bürgerweide car park is located outside the low-emission zone. The ÖVB Arena and the exhibition centre remain accessible via Daniel-von-Büren-Strasse, Friedrich-Rauers-Strasse and Falkenstrasse, Kaufmannsmühlenkamp and Findorffstrasse. To use the other multi-storey car parks in Bremen city centre, however, you will need a valid disc.
Motor home drivers do not require a disc if they are driving to or from their pitch on Kuhhirtenweg using one of the following routes: Friedrich-Ebert-Strasse, Wilhelm-Kaisen-Brücke, Werderstrasse, Kuhhirtenweg or Doventor, Martinistrasse, Wilhelm-Kaisen-Brücke, Werderstrasse, Kuhhirtenweg.
For more information on Bremen's low-emission zone see this website.