Regional Rail riders using SEPTA's app during last week's snow and extreme cold likely experienced a fair amount of frustration.

Trains disappearing, then reappearing, on the app. A delay of a few minutes extending to much longer in the blink of an eye. App information not matching the announcements at the station or the website. It all added up to confusion at a time when trains were frequently running much later than scheduled.

SEPTA acknowledged that using the app could be confusing. Another big temperature drop is expected Saturday, which often leads to mass transit problems, and SEPTA officials said they were working to offer clearer information.

"We have to make sure everything is being communicated clearly," said Andrew Busch, SEPTA's spokesman.

The information riders rely on comes from GPS devices on all of SEPTA's vehicles and dispatchers at SEPTA's Market Street headquarters. The GPS data feed three sources of information: the boards at Regional Rail stations; the app's "Next to arrive" function, which reports whether a train is on time or delayed and how late it will be; and the TrainView function, which allows users to watch a train's progress on a map. Announcements at the stations, meanwhile, are generated by information dispatchers provide.

Different origins of information for the app and the announcements can be one source of contradictions, officials said. And the app itself can become confusing as it is tasked with adapting to sudden changes in service that happen during bad weather.

"We're in an extreme weather situation where we have a lot of things happening at once," Busch said. "We had service delays and cancellations."

The app has existed since 2013 but received a facelift last fall. New features included the ability to save favorite routes and the availability of more accurate real-time data, which updates vehicles' locations more frequently. Last week was one of the app's first experiences with widespread scheduling confusion, Busch said.

Among the incidents that caused problems: A car hit a train on the West Trenton Line on Jan. 4, which shut down a portion of that line, leading to incorrect information both on the app and through announcements. In general, trains that are late may be canceled to avoid backups on the rest of the system, or SEPTA can decide to keep them in service, which leads to sudden changes in arrival estimates. Some canceled trains were quickly subbed by backup vehicles that ran the same route but were labeled slightly differently on the app.

All those variations coming through the app can leave users feeling lost as trains' statuses shifts without explanation. The problems, design experts said, indicate an app that isn't providing riders with the kind of information they want to stay abreast of their ride's status.

"It's not more complicated from a technical standpoint," said David Schuff, professor of management information systems at Temple University's Fox School of Business. "What it's a matter of is being in tune with what the users of the app, what information they actually need."

Schuff pointed to Waze, a navigation app, and Venmo, a digital payment app, as designs that are easy to understand and in tune with how people use their mobile devices.

Mobile apps have a limited amount of space to provide information, and designers have to prioritize how to use that space. SEPTA's app was designed largely in-house, Busch said, with input from consultant CapTech of Wayne.

SEPTA's app is being fed a lot of information from a lot of sources, and knowing how to prioritize it for the rider is an ongoing challenge, said Gabriela Marcu, assistant professor in Drexel University's College of Computing and Informatics. A common mistake in app design, she said, is that it's often done from the perspective of the creator, not the user.

"The way that the information is organized doesn't really make sense from my point of view as a rider," she said. "SEPTA's conceptual model of how they keep track of everything is different than the users' conceptual model."

She noted that the app does connect to SEPTA's Twitter account, which reliably provides detailed, nuanced information about the causes of delays, but she had to tap several links to get to it. Having a feed from Twitter front and center on the app could help riders quickly make sense of train scheduling changes. On the other hand, Schuff said, SEPTA's TrainView function labels trains by number, information many riders likely don't use to identify the train to board. Schuff noted that SEPTA's other tech venture, the SEPTA Key, has some of the same problems with its kiosks, which he said are also not very user-friendly.

SEPTA officials are looking at ways to make the app more accurate and more informative, Busch said, and to make adjustments to keep schedule and route changes from making a train drop off the system entirely. They're also working to improve communication to better sync the station announcements and digital information.

"That's going to be a constant work in progress to ensure we're improving that as much as we can," Busch said.