ASHINGTON, May 7 — Drivers in Los Angeles spend an average of 56 hours a year, more than a work week, stuck in traffic. In Atlanta, the figure is 53 hours, double that of just seven years ago, a report on traffic congestion has found.

The Texas Transportation Institute, in its annual report on congestion in 68 urban areas, found that Americans spend three times as much time in traffic as they did 20 years ago. Governments are not building enough roads to keep pace with new businesses and residents, and people are moving and working farther and farther from downtowns.

The study found that the average person spent 36 hours a year sitting in traffic in 1999, up from 11 hours in 1982. Rush hour has grown to six hours each day, three hours each morning and three hours each evening, twice as long as in 1982.

All this congestion comes with a price: $78 billion a year in wasted time and burned gasoline, the study said. The institute, part of Texas A&M University, analyzed data from the Federal Highway Administration and 11 state highway departments and ranked the areas according to the additional time it took motorists to drive during congested periods as compared with the rest of the day.

Los Angeles had the most congested highways, costing residents an estimated $1,000 per person in wasted time and gas as they spent 56 more hours a year on freeways than they would have had to spend on the roads if traffic moved freely. In New York City and its suburbs, the average resident sits in traffic an extra 34 hours a year and spends an average of $595 in wasted time and gas.

In the Atlanta area, where the population grew by more than one-third from 1990 to 2000, the number of hours motorists sat in traffic more than doubled to 53 in 1999 from 25 in 1992.

The congestion in Nashville, where the population rose by a quarter in the last decade, followed suit. The average resident there spent 42 extra hours in traffic in 1999, up from 15 hours seven years earlier.

In the San Francisco-Oakland region, residents spent an average of 42 hours a year in traffic in 1999, up from 38 hours in 1997. And residents in and around the District of Columbia were stuck in traffic, on average, for an extra 46 hours in 1999, as compared with 44 hours in 1997.