The Freiburger Verkehrs AG is the biggest public transport operator in Freiburg with more than 800 employees. Public transport is very important for Freiburg to reach its climate goals as green city. Every year the company transports nearly 80m passengers with its 67 trams and 62 buses. Additionally, the Freiburger Verkehrs AG operates the Schauinsland cable car which carries over 300,000 guests a year to the top of the very popular destination Schauinsland, the highest mountain in the city.
A requirement that the existing VAG bus fleet meet at least EURO 5 standard forms part of the company’s environmental strategy. Other elements of this strategy include using 100% green energy in tram operation and a tram washing system which collects and reuses rainwater.
In 2010 VAG Freiburg decided to retrofit buses with particulate- filters. 5 buses were retrofitted, going from a EURO 3 standard to EURO 5. Two options were available to ensure that the whole bus fleet met its obligatory EURO 5 standard: either sell the buses and buy new ones, or retrofit the existing stock. The decision to retrofit the buses instead of replacing them was the more cost effective option for achieving the set emission goals. VAG used this project as a pilot to gain experience, as this type of retrofitting was not well established in the market at the time and few other companies had experience in this area.
VAG decided to retrofit its buses with a complete system that was offered on the market rather than buying individual components. In a first step a market analysis was carried out to learn about the available suppliers and systems. The decision to buy the same system that was already being used in newer buses reduced the range of systems to choose from. As the estimated project costs were well below the EU limit for European-wide tenders, VAG requested offers only from possible suppliers of the SCRT system. The offers were analysed and the supplier with the best offer was chosen.
The supplier of the SCRT system commissioned TÜV Nord (a German testing institute) to measure the gaseous and particulate pollutants. Different measurements on an engine test bed were carried out. The engine was measured with and without the retrofitting system. The test results showed that the retrofitting system reduced CO emissions by 92.5%, NMHC by 92.25%, NOx by 81.5% and PM (particulates) by 78%.