This article is part of an ongoing collaboration between Pranav Badami and me analyzing real-time NJ Transit data that we scraped. You can find the previous article here.

With spring break descending on Princeton University’s campus this week, many students are taking this opportunity to escape the Orange Bubble for a bit. Whether you’re going home, flying around the world, or just making a short trip to New York City or Philadelphia, chances are taking NJ Transit will be a part of your journey.

Every day, the “Dinky,” or the Princeton Shuttle, as it’s officially referred to as by NJ Transit, transports countless passengers back and forth between the Princeton and Princeton Junction train stations, serving as a crucial link between the Princeton campus and the rest of the NJ Transit system for commuters, tourists, and students alike. Plus, with a consistent travel time of 5 minutes, the Dinky generally beats traffic if you manage to catch it on time.

Surviving multiple station changes in its recent history, the Dinky is truly Princeton’s “Ol’ Reliable.” In fact, it’s so reliable that we actually decided to exclude it in our systemwide analysis because it was biasing our results. According to NJ Transit’s real-time data feed, 99%¹ of Dinky trains leave within the minute that they are scheduled to, regardless of the direction they are traveling in.

Unfortunately, the rest of NJ Transit is far from reliable. For those who have taken NJ Transit in and out of Princeton, we’re all too familiar with the frustrating experience of missing the Dinky due to a delay on the Northeast Corridor line. In our previous article, we found that roughly 25% of NJ Transit trains are late² across the entire system, with rush hour aggravating delays even more. In this article, we’re going to zoom in on trains coming into Princeton Junction and see what the chance is that you’ll miss the Dinky you originally thought you could make.

Analyzing trains going into Princeton Junction

First, we’re going to split our analysis according to whether trains are north or southbound. Northbound trains are those originating out of Trenton Transit Center, which is also connected to Philadelphia via the SEPTA, while southbound trains are those coming from New York Penn Station, which includes the Newark Liberty International Airport stop along the way. To start off, let’s get a baseline for how often these trains will be late by the time it gets to Princeton Junction.

(All analyses based on data collected from 2/5/18–3/4/2018)

Interestingly, even though Trenton is only 2 stops away from Princeton Junction, it looks like more than half of trains heading north on the Northeast Corridor line are already late by the time it reaches the Princeton Junction station. After digging into this a bit more, our data seems to suggest that this is driven by trains leaving late out of Trenton Transit Center (perhaps something for us to explore in a future article). Meanwhile, southbound trains on the line fare a little better, with a third of trains arriving later than scheduled once they reach Princeton Junction. Obviously, lateness is never ideal, but to assess the practical consequences, we went another step further to determine how often these latenesses would have actually resulted in someone missing the Dinky that they should have been able to make, based on the schedules.

Now, the picture is a little less bleak. Still, almost 20% of trains out of Trenton suffer delays that would cause one to miss the Dinky. This certainly does not bode well for people coming from Philadelphia or Trenton. For those coming from the north, it doesn’t look as bad, with just over 10% of southbound trains being delayed badly enough to cause you to miss your Dinky.

How much time should you leave as a buffer between stops?

For prospective travelers, we plotted the likelihood that you would miss your Dinky based on the number of minutes you are scheduled to wait for (95% of trains have a connecting Dinky within an hour of arrival).