New York City in 1900 was buried under roughly four million pounds of manure every day. But the worst pollution problem was the air loaded with bacteria-carrying dust, through which respiratory diseases were transmitted. When autos displaced horses in the 1920s, he says, tuberculosis rates plummeted. Indeed, hydrocarbon emissions fell 35 percent from 1984 to 1993, thanks to more efficient cars and cleaner gas. You can never build enough roads to keep up with congestion.
Traffic always rises to exceed capacity.
Part of the problem, operations engineer Dietrich Braess showed in 1968, is that adding new routes often makes congestion worse, not better. That paradox seems to have vexed every age. Traffic jams were so bad in Rome 2,000 years ago that the city banned chariot riding during peak hours. Trolleys were overcrowded within five years of electrification. The U.S. built the first interstate highways in the early 1920s, and they were already jammed by the end of the decade.