The U.S. Postal Service is trying to avoid the omnipresent gridlock along Interstate 880 by dispatching its overnight Express Mail from Fremont to Oakland on Bay Area Rapid Transit trains.

"Is this an endorsement of BART? You bet," said Dan DeMiglio, Postal Service spokesman in Oakland. He said the new operation was "close to flawless. We're delighted."DeMiglio said he believed this was the first time in nearly 40 years in the Bay Area and possibly the country that mail had been moved by rail.

From 250 to 340 pieces of Express Mail moves between Oakland and the cities of Fremont, Hayward and San Leandro each day.

Looking to improve their premier service, an Express Mail team came up with the idea more than a year ago. Although Express Mail shipments have never been held up because of traffic, DeMiglio said it would have been inevitable, given increasing traffic.

"As anyone knows, the 880 corridor is a nightmare virtually all day and all night," DeMiglio said.

While ruminating the options, DeMiglio said, "someone innocently said, `Well, let's take BART.' We all looked at each other and said, `Yeah, why not?' "

Months of study followed.

"The idea was so simple and logical and absent of problems - maybe that's why it was so hard to work it through the system," DeMiglio said.

Finally, the post office signed a contract with BART in July. After trial runs, delivery began last month and will continue for a year, when the program will be reviewed.

The round-trip cost to the post office: $4.10.

"You couldn't get a postal vehicle from the Oakland sorting facility to the freeway off-ramp for that," said DeMiglio.

Handoffs will be made at BART stations. The assigned carrier will tote the mail in a locked Express Mail cart "about the size of a person," DeMiglio said.

"It's incredibly efficient," said DeMiglio, noting that potential traffic accidents involving a carrier were "reduced to zero."

While the post office is looking into expanding the service, "I can't say we're planning it," he said. "This kind of thing you move into slowly."