NEW DELHI: Bhopal emits least pollutants and guzzles lowest amount of fuel for urban commute while Delhi is the worst on both these parameters among 14 cities across the country, assessed and ranked by the Delhi-based think tank Centre for Science and Environment ( CSE ).In its study on cleanliness aspect of urban mobility in these cities, the CSE has found that though Kolkata and Mumbai figured at seventh and 10th position respectively in terms of overall emissions and energy consumption, these two emit least among six mega cities due to high usage of public transport and walking.The think tank selected the 14 cities for its study as these are among the most populous in different regions and can be used as better indicators in the race for clean and low carbon mobility. Six of them - Delhi, Mumbai, Kolkata, Chennai, Bengaluru and Hyderabad - are clubbed as 'mega cities' while the remaining eight are grouped as metropolitan cities for the study.The overall analysis was done on basis of combined score to total emissions of heat-trapping carbon dioxide and toxic pollutants like particulate matter (PM) and nitrogen oxides, as well as energy guzzling from urban commuting practices.Kolkata figured at the top among the mega cities for lowest level of emissions and energy consumption, banking on its "public transport culture, compact city design, high street density, short travel distance and restricted availability of land for roads and parking".On the other hand, Delhi, despite being the third highest for share of public transport trips, tanks to the bottom as overall emissions and fuel use are highest due to the sheer number of people, high volume of travel and personal vehicles, and long trip distances."This negates per trip emissions improvement derived from its CNG programme and limited public transport strategy," said the CSE's report - The Urban Commute - which was released in Kolkata on Friday.Delhi has, in fact, highest vehicle stock among these cities. As a result, Delhi emits Particulate Matter (PM) five times more than Kolkata and three times more than Mumbai. Besides, its poor rank is an effect of its relatively higher population compared to other mega cities.The think tank in its study analysed level of motorization, travel demand based on population, share of different modes of transport (public transport, walking, cycling and personal vehicles), average length of daily travel trips and quality of vehicle technologies and fuels to come at its findings."This review has become necessary as greenhouse gas emissions from transport - though the third highest currently among all sectors - has recorded the steepest increase. This is also responsible for health-damaging toxic exposure," said Anumita Roychowdhury, executive director-research and advocacy, CSE.The report attributed the increase in greenhouse gas emission from transport to massive motorisation in the past few years. It noted that it took 57 years (1951-2008) for India to cross the mark of 105 million registered vehicles. But thereafter, the same number was added in a mere six years (2009-15)."Growing dependence on personal vehicles for urban commuiting can lead to irreversible negative trends and damage," said the report while issuing the ranking for those 14 cities.Referring to city-specific ranking where Mumbai emits less and consumes lesser energy for urban commute than Hyderbad, Bengaluru, Chennai and Delhi , it said, "Mumbai's winning streak is a result of its public transport spine - primarily its suburban rail system."Even with the highest per capita GDP among the six mega cities and highest volume of trip generation, use of personal mode is lowest in Mumbai. This has helped the city to have lower emissions and guzzling compared to most other mega cities."Mega cities of Bengaluru, Hyderabad and Chennai score poor as they have lower share of public transport compared to Delhi. They still have scored better than Delhi only because of total travel volumes are comparatively lower given their population levels.Though metropolitan cities have scored better than mega cities due to lower population, lower travel volume and vehicle numbers, they are at risk due to much higher share of personal vehicle trips and high growth rate. Bhopal among them has an advantage of relatively smaller number of vehicles.