Bus & Train trackers explained

About our trackers

Our Bus Tracker and Train Tracker are among the most useful and popular tools we've made available to CTA riders, providing estimated arrival or departure times for bus and train stops across our network. Data from these services also appears in a wide range of apps, like the Ventra app.

Each service uses a combination of real-time vehicle location data (by GPS, track and/or other sensors), historical travel time data and schedule-based info to generate the best possible estimated arrival/departure times with available data.

Reading results: real-time vs. schedule-based information

Both Bus Tracker and Train Tracker prioritize live data based on real-time vehicle locations and rely on schedule-based data when no live data is yet available about a trip.

A good rule of thumb: Three radio waves typically means bus or train arrival information is based on real-time data. Each app or website can make their own design choices, so it is always good to review your favorite trip planning and transit app or website to ensure you understand how it presents schedule-based versus real-time data.

For example, here Train Tracker is showing an estimated arrival based on real-time data, followed by a second estimated arrival based on schedule-based data. The real-time prediction is indicated by the radio-wave icon, and the schedule-based prediction is indicated by a clock icon.

Because real-time data for trains only becomes available once a train has departed its terminal, it isoften important for us tosupplement that information with schedule-based data. This is especially helpful at or near train terminals, where real-time info for any given train is not available until it departs.

What about in apps?

Lots of apps use data we freely share with interested developers as part of our efforts to make it easier to find transit data no matter where you look.

Some apps duplicate or build on our own features, and even do their own blending between real-time and schedule-based info. Apps very commonly use a symbol like radio waves, too, to indicate real-time data versus schedule-based info.

Here's an example from our Ventra app:

How accurate is the information?

Arrival estimates based on real-time data tend to be highly accurate. This info is based on actual vehicle location and, depending on which system it's coming from, known travel times from point to point along our bus and train lines based on historical, observed travel time data which is regularly updated.

No tracking system is perfect, however, and the quality of information our computers can output can be affected by a variety of unpredictable or abnormal factors that affect our tracking systems just as it does most of our peers. These could include:

A trip being adjusted or cancelled to balance service following a delay
A staffing availability issue that affects schedule adherence
A reroute or delay on a line that slows or stops service
A missed terminal departure for any reason (Operator availability, reassignment of resources, a train experiencing an equipment problem, etc.)
Equipment failures or technological limitations, such as poor cellular connections or malfunctioning GPS units

Any of these and numerous other conditions can either make an estimate inaccurate, such as a bus taking much longer to get to you than we expect because of something blocking the street ahead of it.

Why would a bus or train disappear from the trackers?

In some cases, you may see a bus or train disappear from listings because a bus has been removed from service or was diverted along an unexpected path—or in the event a scheduled departure doesn't occur due to an issue at a terminal.

For example, when buses go off their usual route, they disappear from the Bus Tracker system because it can't tell what route they'll take to return to their normal route—once a bus returns to its normal route, it begins showing again in upcoming stops' arrival estimates.

Learn more about some of the other nuances of how Bus Tracker works on its home page.

In Train Tracker, if a scheduled train doesn't depart on time you may see it show "<1 min" or "---" for a bit beyond the planned departure time, in case a train is just slightly delayed. If no train departs for too long, it may roll down to the next one in the list pending a departure where live data can take over. (This sometimes happens when there's an issue with a train, or if people at the terminal are manually modifying when trains depart, separate from the digitized schedule, to rebalance service during or after a problem.)

You can learn more about these behaviors in the page.

How to access the trackers

The CTA Bus Tracker service lets you look up estimated arrival times and other information via the following means:

Bus Tracker on the web (estimated arrivals in your browser) where you can look up stops by picking from lists or typing in a stop ID
Bus Tracker mobile (mobile version of the above)
Bus Tracker by Text (look up stop IDs online or see instructions at bottom of bus stop signs)
Bus Tracker Map (see buses, estimated arrival times by stop or vehicle, and more, on a map in your desktop browser)

The CTA Train Tracker service lets you look up estimated arrival times and other information via the following:

Train Tracker on the web (mobile and desktop-friendly) where you can look up arrivals:
- By manually picking from a list
- By allowing the website to detect your location and show nearby stops
- By searching by stop name
- By entering a train's run number ("follow that train")
- By picking from a list of recent or favorited stops
Train Tracker by Text (look up stop IDs online or see instructions on timetable posters in each station)
Train Tracker Map (see trains and estimated arrival times by stop or vehicle on a map in your desktop browser)

Quick links

Schedules Fares Maps

Alerts Trackers Ventra

System status snapshot

Systemwide

New Schedules in Effect (All Bus Routes)

‘L’ route status

Red Line

Normal Service

Blue Line