Rickshaws, generally, are massive polluters. The majority of them are run with extremely inefficient and polluting small diesel engines. There are a new crop already that run on compressed natural gas that are becomming more common in India. But even less common than that, are new electric rickshaws that use really low-tech components to save energy and the environment.
Richshaws are low-tech vehicles that basically serve as taxis in less developed countries. They're extremely minimalist, using the smallest engines and the cheapest materials they can get away with. I'm sure this thing is powered by lead acid batteries, and yeah, the electricity comes from coal, but it's enough to keep high-emissions diesel engines off the road even in a rural town in Bangladesh. When the third world starts adopting these technologies, hopefully it means that the rest of the world will soon be ready to hop on too.
