Americans, who like to come and go as they please, are upset about traffic. In a recent survey, eight out of every 10 cited traffic congestion when asked what aspect of suburban growth troubled them the most. Crime came in a distant second at 47 percent.

There's a reason why people are more concerned with traffic jams than with burglary or muggings. According to the Federal Highway Administration, congestion grew 26 percent between 1982 and 1996. A 1996 study found that the volume of traffic exceeded roadway capacity in 39 out of 70 urban areas surveyed. In 1982, only 10 of those areas exceeded capacity.

The so-called "smart growth" advocates have a solution: use more light rail, the current term used to describe the update of the old electric trolleys most cities abandoned in the 1960s. The theory is that increased light rail use will get people out of their cars and free up some road space. Some advocates claim light rail could carry as many passengers as six or more lanes of freeway traffic.

Unfortunately for the theorists, the reality is quite different. Several urban areas have opened trolley systems in the past 20 years, and not one carries more than 35 percent of the traffic volume of the typical freeway lane. The average is 20 percent. Even during the morning and evening "rush," the impact on traffic is slight. In Portland, Ore. - often considered the greatest light-rail success story - the trolley carries barely 40 percent of the volume of each adjacent freeway lane during peak travel periods.

But even if the new trolleys exceeded ridership expectations, they are much too expensive. In terms of total cost, it would be cheaper to lease each new commuter a car for the rest of his or her lifetime - in some cases, even a Jaguar XJ8 or a BMW 740i.

Light rail has failed to reduce traffic congestion for two reasons. For one, it is slow. New systems average less than 18 miles per hour. Even during peak traffic hours, it takes 50 to 100 percent longer to complete work trips by rail than by automobile. An hour-long drive becomes an hour-and-a-half or two-hour commute. Studies show that other forms of transit, such as subways and express buses, are faster than trolleys, but still generally slower than automobiles.

Second, light rail trips are as convenient as car trips only within a small part of an urban area. This is a disadvantage shared with other forms of transit, even the far more expensive and faster subways. The kind of frequent, no-transfer express service that makes people want to give up their cars is practical only in traditional downtown areas. This is because only the historic downtown areas are dense enough to allow large numbers of people to walk to work from transit stops.

It's true that public transit is the preferred way to commute in some downtown areas: 75 percent in Manhattan, 60 percent in Chicago, and more than 25 percent in Boston, San Francisco and Washington, D.C. However, historic downtowns are no longer where most people work. On average, barely 10 percent of the employment in major metropolitan areas is in downtown. Even in New York City, the world's largest central business district accounts for less than 20 percent of metropolitan employment.

The futility of trying to reduce congestion with new rail lines can be seen in Atlanta. Over the past 20 years, Atlanta has opened the fastest operating subway system in America. It extends 45 miles, has 36 stations and cost about $3 billion. Yet only downtown Atlanta has direct, no-transfer service throughout the area, and less than 1 percent of the area is within walking distance of a rail station. Meanwhile, traffic volume has more than doubled over the same period, producing some of the worst traffic congestion in the country.

As unpopular as it may sound to some, transit is no substitute for the car. The reason is quite simple: Rail systems just can't carry enough people where they want to go in a way that is as fast and as convenient as the automobile. The reborn 19th century trolley may be attractive as downtown furniture - but as a solution to traffic jams, it's proven to be another dead end.

This essay by Wendell Cox, a Heritage Foundation visiting fellow and head of Wendell Cox Consultancy, was adapted from his chapter in "A Guide To Smart Growth," published by The Heritage Foundation (www.heritage.org) and the Bozeman, Mont.-based Political Economy Research Center.