This is fairly obvious because it generates extras trips while drivers are en route to pick up someone and don't have a passenger. If everyone had their own car

This is fairly obvious because it generates extras trips while drivers are en route to pick up someone and don't have a passenger. If everyone had their own car and infinite parking existed, these trips wouldn't exist. And those additional trips as to traffic. These services have advantages, but reducing the number of cars on the road isn't one of them.