Frankfurt's low-emission zone comprises the area between the A5 motorway west of Frankfurt, the A3 motorway to the south of the city and the A661 motorway in Frankfurt's north. Vehicles without the required environmental sticker may not pass through the low-emission zone, breeches thereof may result in a penalty of € 40.00, even if the vehicle would be allowed to pass through the zone based on its actual emission value.

Emission stickers are available at the TÜV SÜD Service Centres or online at TÜV Hessen.

Further information in German is available at: 
DEKRA
vehicle registration offices
www.umweltzone.frankfurt.de

Travelling to Messe Frankfurt

Vehicles without emission stickers are exempt in driving to Messe Frankfurt (Frankfurt Fair & Exhibition Centre). They are permitted to drive to the fairground's "West" or "North" gates and enter there. These gates may be reached from the A5 motorway, either via the A648 regional road, exiting at "Rebstock", or the "Katharinenkreisel" roundabout. Messe Frankfurt's multi-storey car park ("Rebstock") is also directly accessible from the "Rebstock" exit. You are only permitted to drive in the low-emission zone (areas marked in red) if your vehicle displays an emissions sticker.
www.messefrankfurt.com