On average public transit produces 2% of pollution but transport about 28% of riders. (I don't remember where exactly I got the numbers but I've seen them in a

On average public transit produces 2% of pollution but transport about 28% of riders. (I don't remember where exactly I got the numbers but I've seen them in a few places). The buses need to run at night so the people can rely on them during the day -- it's just the price of public transit, the public uses transit way more if buses run on 10-minute interval during off-peak rather than 30-minut interval. (another study I can't find right now). I think as programmers we tend to try and optimize problem for least pollution, but the problem here lies in the domains of sociology and urban planning; we might not be the most qualified people to solve it. For example if buses pollute 3% because of the extra buses on off-peak routes but now more people use them, this would have net effect of reducing pollution.