How can I define a relationship between GTFS’ trips and calendar/calendar_dates tables?

Decoding Your Transit Schedule: How GTFS Trips and Dates Really Work

Ever wonder how your bus or train knows when to show up? A big part of that magic is thanks to something called GTFS, or the General Transit Feed Specification. Think of it as a universal language that transit agencies use to share their schedules with apps like Google Maps and Citymapper. At the heart of GTFS are a few key files that tell the whole story, and today, we’re going to crack the code on how trips connect to specific dates.

The star of the show is the trips.txt file. It’s basically a master list of every single trip a transit agency runs. Each trip gets a unique service_id, which is like its passport. This service_id is the golden ticket that links the trip to a calendar, telling it when to actually operate.

Now, where does that service_id lead? That’s where calendar.txt and calendar_dates.txt come in. The calendar.txt file handles the regular stuff. Imagine a bus route that runs Monday through Friday, all year long. That’s exactly what calendar.txt is for. It lays out the standard service schedule, specifying which days of the week a service runs and the overall start and end dates. So, our weekday bus route would have a service_id, checkmarks for Monday through Friday, and then the start and end dates for the whole year. Easy peasy.

But what about holidays? Or those random days when the train is running on a special schedule? That’s where calendar_dates.txt swoops in to save the day. This file is all about exceptions to the rule. It lets you add or remove service on specific dates. Let’s say that weekday bus route doesn’t run on Thanksgiving. You’d create an entry in calendar_dates.txt with the service_id for that route, the date of Thanksgiving, and a code that says “no service today!” On the flip side, if there’s a special event and a route only runs on that day, you’d use calendar_dates.txt to add service just for that date.

Making it Work: Tips from the Trenches

Okay, so how do you make sure all these files play nicely together? Here are a few things I’ve learned over the years:

• Keep it simple with calendar.txt: For regular, recurring schedules, calendar.txt is your best friend. It keeps things clean and organized.
• calendar_dates.txt is for exceptions, period: Don’t try to use calendar_dates.txt to define regular service. It’s meant for those one-off situations.
• Unique IDs are key: Make sure your service_id values are unique across both files. Otherwise, things can get confusing fast.
• Dates, dates, dates: Double-check that all your dates are in the right format (YYYYMMDD). A simple typo can throw everything off.
• Test, test, test!: Seriously, test your GTFS feed like crazy. There are plenty of validation tools out there that can help you catch errors before they cause problems.

Getting your GTFS data right can seem like a pain, but it’s worth it. Accurate schedules mean happy riders, and that’s what it’s all about. So, dive in, experiment, and don’t be afraid to ask for help. The GTFS community is full of people who are passionate about making transit work for everyone.