Metro

Next bus in 3, 2, 1 . . . 20 minutes?!

08bps- 3/7/2016- Boston public school students are participating in a walkout Monday and a demonstration at the State House as part of a national protest against proposed budget cuts here and in several other cities. The walkout began at about 11:30 a.m. At Boston Latin Academy, more than 100 students gathered at the corner of Quincy and Warren streets, packing an MBTA bus headed downtown as they sought to convey their worries about how spending reductions could affect their education.(Pat Greenhouse/Globe Staff)
Pat Greenhouse/Globe Staff

When she takes the 32 bus to work from Jamaica Plain, Kara Solomon uses a smartphone app, Transit, to time her walk to the bus stop.

And while she doesn’t expect the app to be minute-perfect, Solomon said it is especially frustrating when the bus disappears from the screen right before it is supposed to arrive, and she has to wait around for the next scheduled trip.

“If the bus tells me it’s coming and it doesn’t show up for two more minutes, that’s not the end of the world,” she said. But when it simply doesn’t arrive, “that’s ridiculous,” she said. “An MBTA-endorsed app says the bus should be here.”

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In the transit world, they are called “ghost buses” because they show up on scheduling apps, but not in real life. Those buses are either really late or were canceled or diverted to another route, yet the change was not correctly reflected in the data feeds the apps receive from the Massachusetts Bay Transportation Authority.

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“It should be peace of mind, seeing it on the app,” said Somerville resident Rebecca Sorrell, who rides the 90 bus to Sullivan Square and charts its progress with two apps that she says are regularly wrong.

Apps such as Transit, ProximiT, and NextBus are made not by the MBTA, but by private developers who rely on transit agency data to estimate wait times and show scheduled arrivals. The apps use a combination of GPS information that periodically broadcasts the location of each bus along its route, and the T’s published schedules, to estimate arrival times. But when a bus is canceled or otherwise diverted, the apps still often default to showing that trip’s scheduled arrival time at each stop. The MBTA also tracks buses on its website.

“We think real-time information is magical, and it’s not so magical if it doesn’t show up,” said MBTA chief technology officer David Block-Schachter. “If we could eliminate this, I think it would give people more faith.”

The accuracy of phone apps is particularly key for the bus system, which is the least reliable of the MBTA’s modes. Buses are frequently delayed by traffic or canceled outright because of driver absenteeism.

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For subways, the system that predicts arrival time also struggles sometimes. But passengers can generally rely on trains coming every few minutes throughout the day rather than on scheduled runs. Subways really struggle when a disabled train, tripped signal or other malfunction causes delay, and the T has a difficult time predicting when repairs will get the system back online.

And for the commuter rail, phone apps give an approximation of where trains are along their routes, and the T recently upgraded to provide more frequent — and accurate — estimates.

Block-Schachter said the T is now hoping that upcoming technology upgrades will make those scheduling apps much more accurate.

The agency has begun outfitting buses with new versions of GPS that provide more frequent updates of bus locations — every 2 to 5 seconds, instead of once a minute or so. That should produce more exact predictions of arrival times.

Meantime, the MBTA is in the market for a new data-collection system that will incorporate GPS, schedules, weather, traffic conditions, and other factors, resulting in even more accurate information. The T hopes to have that selected by the end of 2018, and then next year new scheduling and dispatching software that should also cut down on ghost buses falsely appearing on phone apps.

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“We’ll be able to remove layers of that uncertainty bit by bit over the next couple of months,” Block-Schachter said.

‘It should be peace of mind, seeing it on the app.’

But another problem is that the design of the apps makes it hard for commuters to know if they’re seeing the most accurate and up-to-date information.

For example, Transit uses small curved lines to indicate when a projected arrival time is based on the bus’s GPS location, but no lines when the estimate is based on the published schedule. The small lines can be hard to see, and some commuters probably do not even know they are likely to be more accurate than times based on the schedules.

Block-Schachter said riders should be skeptical of arrival times based only on schedules, noting they are less reliable than those based on GPS.

Stephen Miller, a spokesman for Transit, said the company is updating the screen design to make it clearer whether a trip is relying on GPS information or just a schedule.

Adam Vaccaro can be reached at adam.vaccaro@globe.com. Follow him on Twitter at @adamtvaccaro.