As machines go, the car is not terribly noisy, nor terribly polluting, nor terribly erous; and on all those dimensions it has become better as the century has grown older. The main problem is its prevalence, and the social costs that ensue from the use by everyone of something that would be fairly harmless if, say, only the rich were to use it. It is a price we pay for equality. Before becoming too gloomy, it is worth recalling why the car has been arguably the most successful and popular product of the whole of the past 100 years—and remains so. The story begins with the environmental improvement it brought in the 1900s. In New York city in 1900, according to the Car Culture, a 1975 book by J. Flink, a historian, horses deposited 2.5 million pounds of manure ( 粪 ) and 60,000 gallons of urine ( 尿 ) every day. Every year, the city authorities had to remove an average of 15,000 dead horses from the streets, it made cars smell of roses. Cars were also wonderfully flexible. The main earlier solution to horse pollution and traffic jams was the electric trolley bus ( 电车 ). But that required fixed overhead wires, and rails and platforms, which were expensive, ugly, and inflexible. The car could go from any A to any B, and allowed towns to develop in all directions with low-density housing, rather than just being concentrated along the trolley or rail lines. Rural areas benefited too, for they became less remote. However, since pollution became a concern in the 1950s, experts have predicted—wrongly—that the car boom was about to end. In his book Mr. Flink argued that by 1973 the American market had become saturated, at one car for every 2.25 people, and so had the markets of Japan and Western Europe (because of land shortages). Environmental worries and diminishing oil reserves would prohibit mass car use anywhere else. He was wrong. Between 1970 and 1990, whereas America’s population grew by 23%, the number of cars on its roads grew by 60%. There is now one car for every 1.7 people there, one for every 2.1 in Japan, one for every 5.3 in Britain. Around 550 million cars are already on the roads, not to mention all the trucks and mocorcyeles, and about 50 million new ones are made each year worldwide. Will it go on? Undoubtedly, because people want it to.