If you’re a transit rider that doesn’t live steps away from a subway, then you probably have a transit app on your phone that’s in heavy rotation. But how accurate are these apps?

It all starts with transit agencies, like the TTC, making their data about arrivals, departures and schedules available to third-party app developers. Those companies take that information, sometimes add in historical performance on routes, among other things, to make available real time predictions.

Luc Hartwick who leads the business development at RocketMan App says each app has different ways of analyizing the data and different priorities.

“What makes Rocketman really unique is that we are focused on time,” says Hartwick. “When you think of the commuter you think about their expectation that their vehicle will arrive on time and get to the destination on time. And any sort of disruptions or changes to that are tough for people.”

Those disruptions, like a bus or streetcar not coming on time – or at all – are some of the most common complaints. Which is the entire point of using them, isn’t it?

CityNews asked followers on Facebook what their favourite apps were to use when it came to their commutes: Transit, Rocketman, Google Maps and the TTC website were the most common ones named.

On Instagram, a poll asking whether or not people use transit apps produced some interesting results. Out of 407 responses, 184 people said they do use them while 223 said they don’t. Out of 10 direct messages telling us which apps were the most popular, Rocketman came out on top, Transit was second, with TTC, Google Maps and Citymapper tying for third.

So how do these apps work anyway?

According to Mina Mitry, founder of Kepler Communications, a Toronto-based company that designs and launches satellites into space, a lot of complex systems for moving this data have to work seamlessly for it to work accurately, which is not an easy problem to solve.

“You have to deal with a lot of stuff, like orbital debris and you have to make sure that you have a really accurate timestamp,” he says. “For two, you need to be able to handle millions or hundreds of millions of requests that come in every second. That’s a separate problem to solve. Imagine if 100 million people were coming to talk to you at the same time, just internalizing that as a communications channel the challenge is pretty large in scope.”

While these apps run off of GPS systems, it’s not just the GPS that makes up the accuracy of information. Mitry says you also have the cellular signal that they try to use similar to the way GPS points to your position to triangulate from cell towers where your position is. That’s why you often find discrepancies between these different applications.

Hayley Waldman, communications advisor at TTC, says while it provides the data to these developers, it doesn’t take any in return.

“So at this time we don’t gather any information from any of the apps,” she says. “Those apps help with that and so we’re willing to work with them but we still have our own tactics to inform our service planning.”

CityNews producers put some of the apps to the test to see if they predicted the timing of a route accurately. Here’s how one producer’s journey went.