When the I-66 extension opened three months ago, some District officials feared traffic leaving the new highway would only worsen morning and evening congestion on their side of the Theodore Roosevelt Bridge.

But those looked-for backups have not come to pass, officials say.

In fact, officials say rush-hour delays along Constitution Avenue NW, the E Street Expressway and the Potomac Parkway have increased an average of only two to three minutes.

"There is probably a little more delay coming off the bridge," said George W. Schoene, assistant director of the District's transportation department in charge of traffic engineering. "But the traffic flow is lighter than it could have been."

In December, traffic officials predicted I-66 would funnel up to 700 additional cars an hour across the Roosevelt Bridge during the peak hours of the morning and evening. But data collected earlier this year indicates the actual traffic flow is closer to 600 more cars an hour, Schoene said.

Last February, an average of 12,402 cars entered the District on the bridge between 7 and 9 a.m., an 11 percent increase over the 11,170 cars recorded for the same time a year ago, Schoene said.

During the evening rush between 4 and 6 p.m., 8,725 cars left the city by the Roosevelt Bridge--a 6 percent increase over the 8,230-car average in the previous year, Schoene said.

The modest increases were due, in part, to commuters avoiding the Roosevelt Bridge and using the George Washington Memorial Parkway and Memorial Bridge, Schoene said.

The most remarkable increase in Roosevelt bridge traffic is now at midday, Schoene said. In that period, the number of inbound cars has soared by 26 percent over the year before, and outbound traffic by 11 percent. But no one knows why.

"We don't know whether those cars are going to I-66--since it's open to all drivers--or to Rosslyn," Schoene said.