Environmental zone
Most of Cologne’s metrolpolitan area is a low emission zone, into which only vehicles sporting one of the stickers for emission groups 3 and 4 (yellow or green sticker) are allowed to enter since January 2013.
The Koelnmesse exhibition center is, however, accessible for all types of vehicles, even if they do not bear one of the aforementioned stickers. You will find directions on how to reach the site without a sticker at map low emission zone (pdf) including highway connections.