GTFS-realtime is a feed specification that allows public transportation agencies to provide realtime updates about their fleet to application developers. It is an extension to GTFS (General Transit Feed Specification), an open data format for public transportation schedules and associated geographic information. GTFS-realtime was designed around ease of implementation, good GTFS interoperability and a focus on passenger information.
The specification was designed through a partnership of the initial Live Transit Updates partner agencies, a number of transit developers and Google. The specification was introduced and released under the Creative Commons Attribution 3.0 license in August 2011.
How do I start?
Overview of GTFS-realtime feed types
The specification currently supports the following types of information:
- Trip updates - delays, cancellations, changed routes
- Service alerts - stop moved, unforeseen events affecting a station, route or the entire network
- Vehicle positions - information about the vehicles including location and congestion level
Updates of each type are provided in a separate feed. Feeds are served via HTTP and updated frequently. The file itself is a regular binary file, so any type of webserver can host and serve the file (other transfer protocols might be used as well). Alternatively, web application servers could also be used which as a response to a valid HTTP GET request will return the feed. There are no constraints on how frequently nor on the exact method of how the feed should be updated or retrieved.
Because GTFS-realtime allows you to present the actual status of your fleet, the feed needs to be updated regularly - preferably whenever new data comes in from your Automatic Vehicle Location system.
The GTFS-realtime data exchange format is based on Protocol Buffers.
Protocol buffers are a language- and platform-neutral mechanism for serializing structured data (think XML, but smaller, faster, and simpler). The data structure is defined in a gtfs-realtime.proto file, which then is used to generate source code to easily read and write your structured data from and to a variety of data streams, using a variety of languages – e.g. Java, C++ or Python.
The hierarchy of elements and their type definitions are specified in the gtfs-realtime.proto file.
This text file is used to generate the necessary libraries in your choice of programming language. These libraries provide the classes and functions needed for generating valid GTFS-realtime feeds. The libraries not only make feed creation easier but also ensure that only valid feeds are produced.
To participate in discussions around GTFS-realtime and suggest changes and additions to the specification, join the GTFS-realtime discussion group.
Google Maps and Live Transit Updates
One of the possible applications that uses GTFS-realtime is Live Transit Updates, a feature within Google Maps that provides users with realtime transit information. If you are working for a public transportation agency that is interested in providing realtime updates to Google Maps, please visit the Google Transit Partner Page.