In most cases cars are a less effective alternative. In my city people like commuting to work by car. If they, at least, got on 3-4 people in the same car we could reduce traffic jam by 60% to 75%. What is interesting is that people commuting to work by car as a single and lonly passenger are the ones that complain the most about traffic jam. You would never hear someone commuting by train or tram complaining about the same.