According to automatic passenger counters, between fiscal years 2014 and 2015 ridership declined on Muni motor coaches by by 3.4 percent and on trolley coaches by 7.3 percent. Wait, what? Muni has only felt more and more crowded, right?

The data doesn't add up because those numbers, invoked in an audit of the SFMTA performed by regional transit planners at the Metropolitan Transportation Commission, are incorrect.

The flawed stats stem from flawed automatic counters, which haven't been working properly since at least 2014, or so SFMTA spokesperson Paul Rose tells SFBay. Even then, only 40 percent of Muni buses possess counters, which are placed randomly throughout the system, and 250 of those across Muni are particularly unreliable aging, "legacy" counters. Indeed, manual checks on 250 Muni trips indicated that the counters were underestimating ridership by nine percent. One hypothesis: The horizontal sensors just don't work well during crowded conditions.

“We should have been much more vigilant about catching [the errors] and taking corrective actions,” said director of transit John Haley. Historical undercounting of ridership has persisted thanks to other Muni policies, such as discounting special events like Pride and Bay to Breakers in ridership counts. Further, the T-Third line hasn't ever been counted, because train ridership counts are done manually, and only ever eight years. Numbers for the T-Third line, which opened in 2007, are therefore not yet available.

According to the MTC, the "SFMTA reports it is working to ensure that ridership data is accurate, and that both legacy and future (automatic passenger counters) systems are properly operating... It is also starting to regularly track other indicators of ridership." One big change will be built-in: Better sensors on new Muni vehicles. “The new vehicles will not only provide more reliable service, but they include accurate, state of the art APCs that will count riders more reliably," Rose told SFBay.

Meanwhile, the number of people who actually pays their fare to ride Muni remains a highly unreliable indicator of how many people really take Muni.

Related: Ask A San Francisco Native: Has Muni Behavior Gotten Better, Or Worse?