BART’s new East Bay extension to Antioch is already rocketing off the charts.

Opened in late May at a cost of $525 million, the 10-mile link from Pittsburg to Antioch is averaging 3,800 weekday riders — well above the 2,800 BART initially estimated.

“And there likely would be even more riders, but there’s no room in the parking lot,” said BART Board Director Joel Keller, whose east Contra Costa County district includes the new station.

The 1,006-slot parking lot, which already is being restriped to allow for more than three dozen extra vehicles, is usually filled by 5:55 a.m.

BART “underestimated the parking,” said Antioch Mayor Sean Wright. As a result, riders are parking all day on neighborhood streets.

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Now the transit agency is moving to add 700 parking spaces on seven acres it owns adjacent to the station. But if that doesn’t do the trick, it could reopen the long-standing debate among BART directors over whether building more parking is the best way to promote the use of public transit.

Keller said he “fully supports” getting commuters out of their cars, but in this case there isn’t adequate bus service in the area.

“Wouldn’t it be better to divert people off the roads and onto transit rather than have them continue driving to the urban core?” Keller asked.

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