SAN FRANCISCO (CBS SF) — A malfunctioning toll lane sensor led to 32,000 Golden Gate Bridge commuters being overcharged for their daily trip into San Francisco, according to transit officials.

Bridge officials went public with the overcharging disclosure on Monday and promised refunds would be doled out over the next four to six weeks.

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And just how much money will be refunded? Bridge district spokesman Paolo Cosulich-Schwartz said that is still being calculated.

The district has identified about 32,000 such transactions since early April, according to Cosulich-Schwartz, which is less than 1 percent of all transactions over that time period.

Larkspur commuter Matt Eggers told the Marin IJ that he discovered he had been overcharged in early June. In checking his FasTrak account, he discovered he had been charged $23.10 for one trip across the bridge on May 3.

Eggers said he contacted FasTrak and arranged to have the overcharge credited back to his account.

“They should have caught it sooner,” Eggers told the paper. “But as long as they’re public about it and refund it and commit to better control so it doesn’t happen again, I’m fine with it.”

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Cosulich-Schwartz said the sensor incorrectly counted the number of axles on a vehicle, charging the driver much higher tolls.

The bridge, which no longer has human toll takers, relies on the sensors and the FasTrak system to automatically bill commuters. The tolls for standard two-axle vehicles range from $7.70 for FasTrak commuters to $8.70 for drivers without FasTrak.

Vehicles with three or more axles are charged considerably more.

Cosulich-Schwartz said the sensor had been shutdown for repair. Other sensors have been checked to make sure they were functioning properly.

“We took the equipment and lane out of service and we are automatically refunding the excess toll charges to customers’ accounts,” he said.

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In July, commuters will be facing toll increases. For two-axle vehicles, the tolls will range from $8.05 for FasTrak commuters to $9.05 for those without FasTrak.