In general, buses are cheaper and much more flexible to operate than trains. But a visit to Bangalore made me wonder if it can really thrive as a city without a metro system (which it is currently in the process of building). Bangalore is very dense and the streets are, for the most part, very narrow. Congestion is already terrible, and is composed mostly of auto-rickshaws, motorcycles, and scooters. The city already has many buses, that move dreadfully slowly. To get from the airport into the business district, a distance of 40 kilometers, takes a minimum of 90 minutes.
People who know these things better than I have told me metro systems are never cost effective. In this particular case, however, I can't help but wonder.