Imagine two small towns of 1,000 people: Blacktop and Parktown. In the urban sprawl that is Blacktop, all the residents own fuel-efficient cars (15 km/liter) and travel an average of 20,000 km per year. Over in Parktown, the situation is somewhat different. Good public transport and well-planned amenities mean that only half the inhabitants need a car. Those that do own a car tend not to need it so often and therefore replace it less frequently. Each car-owner drives an average of 10,000 km per year. However, their older-model vehicles are less fuel efficient (10 km/liter) than those in Blacktop. Which community’s transportation is more environmentally sustainable?