That is by design. Bellevue, a fast-growing city just east of Seattle, uses a system that is gaining popularity around the US: intersection (十字路口) signals that can adjust in real time to traffic conditions. These lights, known as adaptive signals, have led to significant declines in both the trouble and cost of travels between work and home.

In Bellevue, the switch to adaptive signals has been a lesson in the value of welcoming new approaches. In the past, there was often an automatic reaction to increased traffic: just widen the roads, says Mark Poch, the Bellevue Transportation Department’s traffic engineering manager. Now he hopes that other cities will consider making their streets run smarter instead of just making them bigger.

Policymakers should start thinking now about how to make sure the appearance of driverless vehicles doesn’t extend the worst aspects of the car-controlled transportation system we have today. The coming technological advancement presents a chance for cities and states to develop transportation systems designed to move more people, and more affordably. The car of the future is coming. We just have to plan for it.

What is the author’s attitude to the future of self-driving cars?

As cultural symbols go, the American car is quite young. The Model T Ford was built at the Piquette Plant in Michigan a century ago, with the first rolling off the assembly line (装配线) on September 27, 1908. Only eleven cars were produced the next month. But eventually Henry Ford would build fifteen million of them.

Modern America was born on the road, behind a wheel. The car shaped some of the most lasting aspects of American culture: the roadside diner, the billboard, the motel, even the hamburger. For most of the last century, the car represented what it meant to be American—going forward at high speed to find new worlds. The road novel, the road movie, these are the most typical American ideas, born of abundant petrol, cheap cars and a never-ending interstate highway system, the largest public works project in history.

In 1928 Herbert Hoover imagined an America with “a chicken in every pot and a car in every garage.” Since then, this society has moved onward, never looking back, as the car transformed America from a farm-based society into an industrial

The cars that drove the American Dream have helped to create a global ecological disaster. In America the demand for oil has grown by 22 percent since 1990.

The problems of excessive (过度的) energy consumption, climate change and population growth have been described in a book by the American writer Thomas L. Friedman. He fears the worst, but hopes for the best.

Friedman points out that the green economy (经济) is a chance to keep American strength. “The ability to design, build and export green technologies for producing clean water, clean air and healthy and abundant food is going to be the currency of power in the new century.”