A new traffic signal computer being used in Prince George's County is cutting fuel consumption, time and cost of motorists on the mile-and-a-half stretch of Branch Avenue, transportation officials say.

The computer system, called Trac, for Traffic Responsive Arterial Coordination,was purchased by the Maryland State Highway Administration for $53,000, according to Tom Hicks, assistant chief engineer for traffic in the highway administration. It was installed last February as a demonstration project. Small computers the size of cigar boxes were attached to traffic light support poles along Branch Avenue (Route 5) at the intersections of Beech Drive, Old Auth Road and New Auth Road.

Since the system was installed, " the (traffic( congestion has almost disappeared" on the heavily traveled commuter route, which handles both incoming and outgoing Beltway traffic and is near shopping centers and auto dealer-ships, Hicks said. About 48,000 drivers use Branch Avenue every weekday, he said.

One result of teh smoother flowing traffic is a saving of fuel. "If traffic is not congested, then (cars are) not unnessarily burning fuel," Hicks said.

Before Trac was installed, the drive down the mile-and-a-half stretch took rush hour motorists about 8 1/2 minutes as their cars churned along at an average speed of approximately 10 m.p.h. An estimated 954 gallons of gas a day in morning and afternoon rush hours alone was burned, according to a study made by the Maryland Department of Transportation and computed by the Georgia Institute of Technology.

When the study was made, traffic on Branch Avenue was more congested than usual, Hicks said, because the "timed" traffic lights at Beech Drive, Old Auth Road and New Auth Road were malfunctioning and were operating independently of each other.

Now rush hour drivers average about 39.5 miles per hour down the same stretch and the drive takes approximately 2 1/2 minutes. Automobiles are now burning approximately 208 gallons of gas each day in morning adn afternoon rush hours, a saving of 746 gallons of gasoline each day in rush hours alone, the study showed.

Trac "has done its job so well so far that we feel we should proabbly do a more in-depth study with it on a bigger system," Hicks said. He has requested that the chief state highway engineer enlarge the program. While the test results so far are "indicative of good things, it doesn't necessarily prove anything yet," he said, because the first test "was very simple." Test results on a larger scale "may not be quite so startling," he cautioned.

Hicks said the Trac equipment would "cost us more (than soem conventional "timed" traffic signal systems), but the good that will come from it will more than offset the initial cost."

The chief difference between Trac and the old "timed" light system on Branch Avenue is that the Trac system is more flexible, Hicks said. The traffic lights can readjust their timing every time the light goes through a complete cycle of green to red and back to green. Under the old system, lights were "lacked into three cycle lengths," he said. They could-accomino date heavy, moderate and light traffic, and could adjust to inbound, outbound or average flow of cars. The lights could also be set in a free flowing pattern, Hicks said, to accomprodate light late evening or early morning traffic. But if there was an accident, or something happened to interrupt the planned traffic flow, the timing of the lights could not be readjusted to meet the current traffic conditious.

The flexible cycle length also makes Trac different from the Urban Traffic Control System that was used in the District on approximately 100 downtown traffic lights. That system, which was established as a reasearch project by the Federal Highway Administration to study ways to control urban traffic through the use of computers, was used about four years. It was discontinued almost a year ago, when the District was to take over its operation, because of increased operating costs.

The former manager of that project. Philip Tornoff, said the District's signal cycel could only be adjusted about every five minutes. Another basic difference between the District's system and Trac, Tarnoff said, was that traffic lights in the District were controlled by a single computer. Approximately 500 traffic [WORD ILLEGIBLE] placed at various points in the street sent signals to the main computer, which would thenprogram the traffic signals to give more "green time" to streats with the heaviest traffic.

The Trac system, which is designed for use on heavily traveled streets with cross streets that aren't so heavily traveled, operates through individually controlled computers.

Marshall McReynolds, president of the Traffic Engineering Supply Company in Alexandria, designed, manufactured and distributed the Trac system. The state of Maryland was his first customer. Nine patents are currently pending on Trac at the U.S. Patent Office, he said. McReynolds said he worked on the system for four years, studying about 100 traffic systems before coming up with Trac.