Thousands of Metro riders who rely on a smartphone app to tell them when their next Metrobus is slated to arrive have been left in the dark after a divorce between tech companies took a nasty turn.

NextBus DC, a popular app available in both a free and paid version, went dead on the evening of Dec. 20 when the company that provides the data stream pulled the plug.

Riders have reported that the application stopped working, then was not available when they tried to download it again. Some riders away for the holidays may discover the problem when they return to their regular commutes this week and find the connection has been lost.

The NextBus technology uses GPS tracking to predict when buses will arrive at a given spot. Metro started it in July 2009 as a solution for riders frustrated that one of every four buses was not showing up on schedule. Riders can access the data by computer or by calling a phone number. Smartphones, though, have been become a popular way for riders to access the information as they wait for buses.

Metro distanced itself from the fracas and said the NextBus DC app is not officially supported by the transit agency, noting that riders can still access the NextBus information on the Web or by phone. The three companies involved, though, are pointing fingers and raising questions about what happened.

"The cut of the data came with three days' warning to us, and I still don't understand why," said Ken Schmier, who founded the technology for tracking the buses in California.

Kelly Beener, co-founder of AppTight, which developed NextBus DC in Austin, Texas, said her company received no notice and hasn't been able to get any answers as to why the data for its D.C. feed, but not its San Francisco feed, was cut off. Meanwhile, she said, riders are flooding her inbox with questions about what happened.

"It's not working because of the end of the contractual relationship between NextBus and NextBus Information Systems," explained Lawrence Rosenshein, vice president of sales, marketing and business development at NextBus Inc.

The companies divided several years ago, with Schmier keeping the name NextBus Information Systems and getting to keep a stream of data but losing the bulk of the technology to a Canadian company. But the agreement between the two NextBus companies ended a few weeks ago. NextBus Inc. then ended the data feed because it cost money to maintain it, Rosenshein said.

It was not immediately clear how many people were using the app in D.C. Schmier estimated that the two versions had about 30,000 users locally and he said about 7,000 users have emailed asking what happened to their app. "It would seem to me more effort should have gone into making the transition uneventful for riders," he said.

"The last thing we want to do is keep anyone from accessing the data," Rosenshein said. "The data is still available and the predictions are still available. They just need to change the way they are doing it."

Schmier told riders not to give up on the app. His company, which will be changing its name, will try to adapt its system to a new version of the data stream provided directly by Metro. "We'll work it out. We appreciate everyone's patience," he said. But he warned it could take weeks to redo the programming. "What we don't know is how many of our subscribers we'll lose."