More fresh air. Less dust. Less noise. Shorter transport times for everyone. Congested traffic makes everyone's trip longer and less convenient. Any individual

More fresh air. Less dust. Less noise. Shorter transport times for everyone. Congested traffic makes everyone's trip longer and less convenient. Any individual gains from using a car as opposed to not using a car as long as the traffic is not congested. Too many individuals doing what personally benefits them make it worse for everyone. This is the definition of tragedy of the commons. In the sheep example, every shepherd benefits from using the field, but if too many sheep use the field, it's ruined and noone can use it. Same with congested traffic.