Alan Sipress's Aug. 5 story about Los Alamos National Laboratory scientists who are studying traffic congestion overlooks the fact that advanced technologies already are being used widely to save lives, time and money in surface transportation ["Studying the Ebb and Flow of Stop and Go," front page].

For example, computerized signalization keyed to traffic flow has cut congestion in Atlanta by at least 20 percent and has boosted rush hour vehicle speeds in Southeast Michigan by 19 percent, according to local officials. Minneapolis, Phoenix and other cities use sensors to detect traffic flow and adjust signal timing. In Montgomery County, 200 video cameras and 3,000 traffic detectors in roads and highways are used in a traffic-management system supporting up to 1,500 traffic signals.

The article refers to "the theoretical breakthroughs in Germany" in ramp metering, using lights to feed traffic onto freeways slowly. Ramp metering has been used for years in the United States and has been documented to reduce accidents by anywhere from 15 to 50 percent.

An Aug. 3 Metro story reported that Dulles Greenway officials are planning a toll discount for drivers whose cars bear the Smart Tag transponder ["Dulles Greenway Raises Weekday Toll"]. The use of transponders allows vehicles to zip through toll booths without stopping, whereas drivers without transponders must stop. The same electronic toll-payment technology is used by thousands of commuters in the New York City area, San Diego and elsewhere.

The technologies involved in intelligent transportation systems already are available to transportation authorities. All we have to do is put them to use.

JOHN J. COLLINS

President and CEO

Intelligent Transportation Society

Washington

The recent article on Los Alamos National Laboratory scientists' using physics to research how to deal with traffic gridlock inspires the question of whether this institution -- always enamored of high-tech solutions -- ever considered an obvious low-tech aspect of this issue: population growth.

We can use "technofixes" until the cows come home, but at some point, we need to deal with the fact that the United States, according to the U.S. Bureau of the Census, is now the third-most-populated nation and the sixth-fastest growing, ahead of even Mexico and Bangladesh.

KATE BURNETT

Los Alamos, N.M.