Population growth means more cars on the road and therefore more congestion
Mumbai is a narrow strip of land and so traffic flowed in one direction from the north, so it is always busy in one direction from the north, so it is always busy in one direction during peak hours.
Public transport is already at capacity, so the only option is to use own car so more cars end up on the road. Many people die on the trains every day in mumbai.
Potholes caused by heavy rain during monsoon season causes accidents which hold up traffic.
Rules of the roads are not always followed, poor lane discipline and people swerving on to the road causes accidents which cause long queues.
As mumbai is a narrow strip of land, bottlenecks are caused when lanes converge which causes congestion
Railways and roads stop outside the CBD, so people still need to drive to get in.
Lack of proper drainage systems causes flooding
Rickshaws hold up traffic and cause air and noise pollution