Veteran public transit users know that scheduled departure times rarely match up to actual departures. Google’s announcement this week that it is providing live transit updates for select cities should be welcome news, then, for commuters who often find themselves sprinting after the bus. We caught up with Google to find out how they implemented the system and what their plans are for expansion.

Transit has been a feature of Google Maps since 2005, when the service started providing driving directions for users. Today, Google has transit directions (driving, walking, public transportation) for over 100 cities in the U.S. In many locations, Google Maps also provides scheduled departure times for public transit. But anyone who has ever taken public transit knows that the idea of a “schedule” can be pretty… loose.

So Google is taking the service to the next level with real-time departures for public transportation, as well as service alerts (when a bus won’t go past a certain stop, for example). “We found in continued partnerships with [public transportation agencies] that real-time data is something that folks were not only able to

provide but interested in being able to get,” explains Martha Welsh, strategic partner development manager at Google. Now, instead of agonizing over whether you’ll miss your train as you get a cup of coffee, you’ll know exactly how much time you have.

This week, live updates launched in six international cities: Boston, Portland, Ore., San Diego, San Francisco, Madrid, and Turin. Why were bigger cities like New York or, say, London left out? It all comes down to the transit agencies, many of which don’t have real-time capabilities yet. “Obviously the agencies themselves have to have the capabilities,” says Welsh. “It is

a complicated system to make sure that our system can work with theirs.”

Real-time updates are becoming increasingly common, however, which means that new cities will likely be added soon. “We are excited to bring more cities on over the coming weeks and months,” says Welsh.