Photo by Tim Brown

For multiple years, there was a technical issue that caused WMATA to both under and overcharge Metrorail riders. Some of the affected passengers will receive refunds this summer.

Metro said that “distance calculation errors” caused the system to charge people about $0.05 above and below the amounts they were supposed to pay for trips, based on how far they were traveling on the system. The agency did not specify which routes were affected.

The error cost Metro about $124,000 a year, which is 0.007 percent of its total operating budget, according to the release. It affected fewer than 5 percent of rail trips.

Metro is giving an automatic credit to registered SmarTrip card holders this summer for any overcharges exceeding $2 between 2015 and 2017.

Metro did not disclose the refund amounts in total. It’s also unclear how long the issue has taken place. “We’re still in the process of going through the analysis to determine which riders were affected,” Metro spokesperson Richard Jordan told DCist.

The announcement came a day before Metro implemented its bus and rail fare hikes on Sunday.