Delhi's fight against pollution is likely to hit the diesel roadblock even in the public transport segment. While the Delhi government runs all its buses on CNG, a large number of buses plying in the city are still fuelled by diesel. These are plying as private 'chartered' buses, with most registered as tourist vehicles. This is besides the 92% of trucks that are diesel-based. According to a study conducted by Council of Scientific & Industrial Research (CSIR)-Central Road Research Institute (CRRI) in 2013, on vehicle traffic load, a staggering 71% of buses registered in the city run on diesel. The data was arrived at after looking at a "vintage" vehicle profile of the city, starting from 1980 onwards. S Velmurugan, senior principal scientist at CSIR-CRRI, said, "The study was on vehicle traffic load at 12 intersections. However, the historical vehicular profile of Delhi was also compiled for the study, starting from 1980 onwards till 2013." He said that the profile looked at all the major category of vehicles, including two and four wheelers, autorickshaws, buses and trucks. "The data was clear: of the buses registered in Delhi, 71% were running on diesel, while CNG buses were only 29%," added Velmurugan. This is contrary to the popular view that public transport in the city is entirely CNG-based. What makes the data interesting is the fact that public transport in the city has been entirely CNG-based since Delhi government made it mandatory in 2001. Buses as well as autorickshaws switched to the cleaner fuel after it was made mandatory, with all commercial passenger vehicles also switching to CNG. The exception were tourist buses and taxis, which were allowed to remain diesel vehicles as CNG stations were not available outside Delhi. The study, however, clearly shows that a large part of the daily transport remains diesel-based. While DTC and cluster buses may be CNG-based, most of the tourist buses, which also run as intermediate transport within the city and Delhi NCR are diesel-based. Adding to the diesel load is the large number of trucks registered in Delhi that are also fuelled by diesel. Only 8% were CNG-based in 2013, despite the fact that goods carriers as well as commercial vehicles plying within Delhi are supposed to be running on the green fuel. The number of private vehicles switching to diesel has also gone up in the past few years, adding to the pollution. Since 2008, the number of diesel four-wheelers has been seeing a jump, from 9.6% in 2008 to 14% the next year and 21.4% in 2010. It came down to 13.5% in 2011 and 11.6% the year after. According to experts, the spike in the number of private diesel vehicles has also had a substantial impact on the vehicular pollution in Delhi.