Been snubbed by a Muni bus that didn't stop for you? The SFMTA offers some explanations.

Pedestrians walk past a Muni bus in downtown San Francisco, CA, on Friday November 17, 2017. Pedestrians walk past a Muni bus in downtown San Francisco, CA, on Friday November 17, 2017. Photo: Michael Short / Special To The Chronicle 2017 Buy photo Photo: Michael Short / Special To The Chronicle 2017 Image 1 of / 1 Caption Close Been snubbed by a Muni bus that didn't stop for you? The SFMTA offers some explanations. 1 / 1 Back to Gallery

Does a person even live in San Francisco if they've never been utterly burned by a Muni bus that blew right past a bus stop while people were waiting?

It's a daily occurrence along some bus routes, but it never ceases to infuriate would-be boarding riders. Now, the SFMTA has released five reasons as to why people are sometimes passed up. They will, unfortunately, likely not assuage anyone's anger.

The SFMTA calls these snubs "pass-ups" and notes that "every transit system grapples" with them.

"We know that when Muni riders invest their time waiting for a bus or train," the agency writes in a post, "they place their trust in the reliability of the system to get them where they're going — at the time they planned."

The first reason is an obvious one, particularly for any frequent guests to the 38 and 38R bus lines: "full vehicles."

The San Francisco Municipal Railway – and its associated bus lines – have a long and fascinating history. Click through the gallery to see photos from our archives. The San Francisco Municipal Railway – and its associated bus lines – have a long and fascinating history. Click through the gallery to see photos from our archives. Image 1 of / 54 Caption Close Evolution of SF Muni buses over the decades 1 / 54 Back to Gallery

"When this happens, operators will call in to report the full vehicle and the need to skip stops. In these cases, the operator will generally only make requested stops for passengers to get off," the post continues. "In some cases, however, a vehicle may be crowded only in the front, and an operator may not be able to see room available behind the crowd."

Two additional reasons are mandated by the SFMTA managers, not the drivers. One states that due to safety reasons, operators can only stop once after closing vehicle doors. The other says that sometimes, operators are ordered to skip stops "to even out service when vehicles become bunched up."

The fourth reason is a no-brainer: Buses marked with an "R" — for "rapid" — only make select stops during their routes.

And lastly, there is sometimes what they call a "sign malfunction."

"While operators are expected to ensure that their vehicle's 'headsign' displays the proper route and destination, in some cases the signs may fail without the operator's knowledge," the post reads. "Any vehicle which is 'not in service' should be indicated on its headsign."

So there it is. Next time a bus flies by, riders are encouraged to remember why they may have been left out in the cold. Will it make them feel any better to be left behind, though? Probably not.

Alyssa Pereira is an SFGATE staff writer. Email her at apereira@sfchronicle.com or find her on Twitter at @alyspereira.

