Private cars are responsible for a significant amount of the world's greenhouse gases. Public transport cuts down the number of cars on the roads, and provides transport to those who cannot afford, wish, or are able to drive a car. In addition, public transport use can relieve road congestion, save time on journeys, and be a less expensive mode of transport. Public transport tends to be developed in densely populated areas, and may be neglected in sparsely populated areas. It may be possible to provide some public transport services to less populated areas by employing alternative methods of operation, for instance, by using voluntary community drivers.