This Is Why NextMuni Predictions Are Always Screwing You Over

It's a problem that plagues Muni riders at bus stops every day: The digital NextMuni readout predicts your bus will come in five minutes — a prediction that you quickly realize is frozen in time.

You're in a hurry, and can't decide whether or not to treat yourself to an Uber (or a taxi). The bus stays five minutes away every five minutes for an hour, taunting you. 

Is the bus lost in a time warp? Are hackers gleefully messing with NextMuni? Are we in some sort of transit purgatory?

[jump] Finally, someone has an answer for us. Muni's new self-made blog Moving SF , claims the design of the system itself is to blame. 

According to a blog post by Moving SF , the NextMuni time readout is actually based on the GPS-read distance of the bus from your stop and anticipated traffic patterns. So if a bus is “five minutes away,” it's actually a predetermined distance away that would equal five minutes under ideal conditions.

Instead your bus is snarled in traffic or worse yet — broken down, not moving. Until that bus actually starts moving, the readout will continue to show that same arrival prediction, at the expensive of your sanity. 

From Moving SF's post “Not Your Ordinary GPS — Tracking Your Ride“: 

…there are a number of reasons why vehicles may not arrive when expected. Heavy traffic, breakdowns, and other unforeseen problem can delay or completely interrupt service, which can then throw off the NextMuni predictions.

How does this affect the predictions? NextMuni uses GPS technology equipped on every Muni vehicle and advanced computer modeling to track Muni buses and trains on their routes. The technology takes into account the actual position of the transit vehicle, the intended stops and anticipated traffic patterns. So, when traffic is snarled or your bus or train has a mechanical malfunction, NextMuni predictions often become inaccurate. But you may be surprised to know that in general, the margin of error overall is less than one minute for predictions of five-minutes or less. For 10-minute predictions, the margin of error is less than two minutes.

This doesn't address the issue of ghost vehicles, better known as Muni buses that don't show up in a timely fashion, as predicted by NextMuni. Those vehicles, apparently, either don't have GPS trackers or don't have them turned on, according to

Things could always be much worse, like if  voters had passed Proposition L last week, snarling the already strained Muni system. Then Moving SF would have to create a blog post titled “Why Car Drivers Are Screwing Over Your Transit System — Not Your Ordinary Gridlock.” 

Dodged that bullet.

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