Person scratching head while looking down the tracks

When Things go Wrong

The majority of CTA rides are on-time and uneventful, but sometimes service can be disrupted. Here’s what we do about it.

On an average weekday, the CTA provides about 1.6 million rides on its buses and trains. If that were a city population, it would be the fifth-largest city in the United States (or, in other words, that’s more rides than if the entire population of Philadelphia took a ride on one of our buses or trains each weekday).

CTA ‘L’ trains travel about 221,633 miles on a typical weekday (that’s about seven times the circumference of Earth at the equator). More than 1,800 buses travel over 159,547 miles on a typical weekday (that’s almost another six times around the equator).

And together? The distance our vehicles travel on an average weekday is almost a full trip to the moon and back.

The majority of those rides are on-time and uneventful—but with a system this large and complex, problems do occur. A problem at just the wrong time can affect the commute of thousands of people.

There are countless reasons why service can be disrupted or delayed. In many cases, the disruption/delay is entirely out of CTA’s control. Examples include roadway congestion and situations that require us to call on police or fire department personnel, or people who fall ill while simply riding a bus or train. Though CTA vehicles are well-maintained by experienced staff, mechanical issues can still occur, just as with any vehicle that travels hundreds of miles every day.

Through planning, infrastructure investment, maintenance and operations, we do everything we can to make passenger trips as timely, convenient and comfortable as possible.

Regardless of the cause of a problem, there are many things we do to address them both during and after an incident. We also work hard to prevent them in the first place. We have one overriding goal: To keep our buses and trains running safely and on time 24/7.

To help you better understand a few of the challenges we, as the nation’s second-largest transit system, face, we’ve put together this page to cover some of the causes for delays and what we do to address them.

On this page



On the ‘L’ System

Why do delays happen on the ‘L’ and what do you do about them?

Rail networks are complicated systems and there are a lot of variables that can affect service. The cause of delays can range from equipment problems to people falling ill on their commute.

Knowing that we must deal with the unexpected every day, our schedulers design a little wiggle room into the schedule—this allows for most run-of-the-mill delays, which can be compensated for by a train by simply continuing without further interruption.

If a delay occurs at the peak of a rush period, however—even for just a few minutes—it can cause trains to quickly back-up, resulting in an area of rolling congestion and/or gaps in service in front of the delayed train.

Delays can quickly become compounded: For example, once something has delayed a train, more people will be waiting at stations ahead and the delayed train can become crowded, leaving people behind at each platform. It can then also lead to a train taking longer to stop at each station, falling further behind schedule. As a result, we sometimes have to implement what are known as "service restoration techniques" to space trains out (such as running a train express or holding trains at stations across the line). These options are carefully considered by service management personnel, because they also can cause some additional inconveniences for some riders.

Though we've upgraded huge portions of the 'L' system, we continue to undergo a variety of track and signal upgrades, route renovations and reconstructions across much of the system. Along with new railcars and new or overhauled buses to replace older ones (which can be more likely to have equipment problems), we're doing quite a lot to reduce delays and improve the quality of service on the 'L'.

Still, there are times when delays are simply unavoidable, as with any busy rail system anywhere in the world. Here, we'll outline some of the more common causes of delays, why they happen, and what we do about them...

Equipment Problems (Trains, Signals, Switches, etc.)

Just as bicycles get flat tires and automobiles sometimes break down, train cars—full of complex mechanisms and technology—encounter occasional problems too.

For the most part, our trains run very well. If any one of the many thousands of components on our nearly ~1,400 train cars fails, it can result in a delay and affect the quality of service along its route.

Our operators do more than just drive the train--they go through extensive training and have a great deal of experience for solving problems on-the-go. An 8-car train, for example, has 32 side door sets, 32 motors under the floor, over 64 braking mechanisms alone. Additionally, trains have countless onboard systems for passenger comfort, safety, communications and more. Although a stuck door, a propulsion system error or a brake problem can delay a train, our operators typically only need a few minutes to troubleshoot and get their train moving again.

If a track junction experiences a problem, such as the loss of signals from a neighborhood power outage, we may have to manually throw and lock switches in place before we can get trains moving through safely. This takes extra time and can require trains to operate at restricted speeds to ensure your safety. Signal and switch maintainers are on duty at all hours and, in the event a problem occurs, they often arrive in minutes to begin solving it.

With more than 1,400 railcars traveling nearly a quarter of a million miles a day over 200 miles of track, it’s a tough job and it takes a lot of people working very hard to keep the city moving.

In recent years, much has already been done to improve reliability on the ‘L’: Red and Blue Line subway track, signals and switches have been renovated or completely replaced in recent years; the tracks on the Dan Ryan Line (the South Side Red Line) was completely rebuilt, the Pink Line was completely renovated; several junctions and interlockings were renovated or built for the Brown Line Capacity Expansion Project; and major track replacement work on the Blue Line's O'Hare Branch and Ravenswood-Loop Connector (used by Brown and Purple Line trains between Armitage and the Mart) have been completed over the last couple of summers.

Further, major projects to improve the Red and Purple Lines from end to end are getting underway. A fleet of over 700 new railcars—the 5000-series—was delivered in 2011, which allowed us to expand our fleet and retire hundreds of old railcars. Another new series, to replace hundreds more, are already planned!

Sick Passenger / Medical Emergency

If a person falls ill on a train and is unable to walk, move or is unconscious, we may need to hold a train at a station until paramedics can arrive and provide emergency medical assistance. Everyone's health and safety is a top priority for us, so please be understanding in the event someone becomes ill or falls and gets hurt.

If you see someone who is sick or injured, please notify the nearest employee and/or call 911 right away!

Police Activity

There are a variety of reasons police may require us to halt service on a route and we take safety concerns very seriously.
If we see or someone reports a suspicious package, police may ask us to stop trains while they investigate.

If a crime takes place on or near CTA property, police may ask us to stop service while they look for a suspect, or even evidence, in a crime. (Crime on CTA is actually very low—despite providing what approaches 2 million rides/weekday, crimes are very rare.)

If an employee spots an unauthorized person on the tracks or trespassing in a subway tunnel, we may need to cut power and wait for police to remove an offender.

In any of these cases, safety always comes first, so sometimes we need to temporarily stop service so that we and other people in public safety roles are able to perform their duties.

Minor track fires / reports of smoke / fire department activity

If we receive a report of smoke in a subway, this can also cause delays or a stoppage. Smoke does not always mean fire—in fact, it rarely does. Smoke can be drafted in from up on the street above when someone is cooking or lighting a grill near subway air vents, or could result from an equipment problem such as a set of brakes rubbing while a train is moving.

However, whenever something generates smoke or brings it into the subway, we do have to investigate it and the fire department may additionally require us to hold service while they also check things out. (Safety first!)

Minor track fires can sometimes occur, though. For example, newspapers and other debris (food wrappers, etc.) can get blown into subway tunnels by strong air currents as trains enter and leave stations. Once on the tracks, debris can collect and become kindling for fires, since sparks are a normal thing under electric trains powered via third rail.

To help avoid disruptions to service, please don’t leave newspapers on benches, on the ground, on top of bins or other station fixtures. We also ask that you don't leave newspapers in the train, either, since they can get blown or tracked out of cars onto platforms—be sure to take newspapers and all other items with you when you leave (and recycle them, if you can).

Also, fires near our tracks can also cause delays. In 2011, for example, a large fire broke out at furniture warehouse next to the elevated tracks just north of Fullerton Avenue—causing a disruption to Red, Brown and Purple Line service for about four hours. We were able to restore service only after the fire department determined it was safe to do so.

Keeping you informed

One of our biggest priorities during an incident is keeping you informed of what’s going on and to help you make informed decisions when the unexpected happens. To do this, we use multiple channels: Platform and onboard announcements, alerts on our website and sent directly to you by e-mail and text, electronic information screens; and even alerts via Twitter.

The nature of every incident is different, and disruptions by their very nature are fast-changing—as is the information about them. We’ve recently implemented a number of improvements to how we communicate delays consistently and in a widespread manner, and we're always working on ways to do more.


Why do trains sometimes break down?

Our maintenance crews work hard to keep our operating equipment in good shape. Many of our railcars have been in service since the 1980s and now nearly twenty years beyond what their designers would reasonably have expected.

The good news is that we've just replaced our oldest railcars (some dating to the late 1960s), and our modern 5000-series cars feature state-of-the-art propulsion technologies and other features for better reliability. Improvements to these cars come from design considerations that incorporate our 120+ years of institutional experience running train service combined with the latest in computerized controls and diagnostic equipment. The average age of our fleet is now much younger than it was just a few years ago, reducing maintenance needs and the number of failures that occur. New technology helps us identify and fix issues more quickly, and has increased the number of cars available for service.

We're also overhauling our 3200-series cars (at present, primarily used on the Brown and Orange Lines), previously our fleet’s newest cars, as they are now more than 20 years old.

Soon, we’ll be replacing more of our fleet with an even newer series of rail car—the 7000-series.


Why do Red Line trains sometimes get rerouted via the elevated lines—or Pink Line trains onto the Blue Line tracks?

If something halts service in the subway, the Red Line has the special advantage of being able to be rerouted away from the subway via elevated lines. This way, trains can still make the whole trip between Howard and 95th via downtown.

We sometimes refer to this as Red Line trains being rerouted “over the top.”

A similar situation is when something disrupts or severely delays service into the Loop: If Pink Line service is disrupted into the Loop, we sometimes will use a track connection between the Pink and Blue Lines near Polk to divert Pink Line trains onto the Blue Line just up to Racine. This allows us to afford Pink Line riders a same-platform transfer to continuing service into downtown via subway (instead of having to ask people to transfer to a shuttle bus, which contends with roadway traffic). This alternative plan can also help us more efficiently turn Green Line trains back toward Harlem with fewer delays and lesser congestion if both lines must be disrupted.

There are a number of other, common reroutes we might implement, too, such as sending Brown Line trains into the subway if there's a problem on their elevated routing, or “through-routing” Brown and Orange Line trains via two sides of the Loop ‘L’ if there's an event that disrupts service on just one side of the Loop.


Why does my train keep stopping for signal clearance?

Trains are kept at a safe distance from the train ahead of it by our signaling systems, which are designed to tell trains to stop if there's a train occupying the tracks ahead.

If something has delayed the train before yours and your train starts to catch up, it may need to stop and wait at a safe distance until the train ahead has moved further down the track. Once it moves, your train can move up, but again may have to stop when it gets too close to wait for additional clearance (such as when the train ahead slows for a curve, stops at a station, or approaches a junction).

If a delay is severe enough, multiple trains can "bunch" up, leading to congestion through an area.

Though congestion can happen anywhere, it can be worse when several trains are approaching a junction all at once. As each train gets through the junction, all the trains behind it, one after another, get to move up. Then, when the next one goes, they move up again, and so forth, until every train is through.

It's kind of like what happens at a stop sign--if there's light traffic, with just two or three cars going through, the wait isn't long and it's barely noticeable. But if there's 20 cars that come all at once, traffic can crawl through the intersection ahead. Even if behind those 20 cars is light traffic, and just one car every 20 seconds is coming up, they'll still end up in congestion until all the traffic cycles through.

An 8-car 'L' train is a lot longer and heavier than a car, though, and requires more space as a buffer. As a result, a delay during busy hours can back up further than auto traffic at a stop sign.


Why do you run trains “express?”

Running a train “express” (not stopping at stations it normally would stop at) is a way to alleviate congestion following a delay.

A delay can cause a gap in service, and it’s important we try to keep service evenly distributed across a route. Running an express train allows that first train following a delay to get ahead and close a gap in service—while also alleviating some of the more immediate congestion where the delay occurred.

A reason that it's really important to close gaps is because this first train, with more people waiting on platforms ahead, can become extremely crowded and take longer at each stop, worsening delays and leading to multiple trains too crowded to pick anyone else up. By sending one or more trains express to spread them out, multiple trains can then simultaneously start picking up people at groups of stations ahead, leading to overall faster travel times.

We understand that it may not feel like a very good solution if a specific express train doesn’t serve your trip, directly: However, when restoring service after a delay, we sometimes need to look at the larger picture of the route and work to restore even intervals between trains. When deciding whether to send a train express, staff considers whether not closing a gap would cause more crowding than it might solve, looking at how best to deliver service to meet demand, and working to get service back to normal as quickly and as effectively as possible for everyone.

Because we know this is an inconvenience to some, so we don’t make the choice lightly and do try to do this only when it's necessary.

On the Bus System

What causes bus delays?

Bus systems, because they have to deal with so many external influences, are an incredible challenge to design.

Schedulers carefully and masterfully weigh a variety of factors into writing schedules while trying to provision service in a way that makes the most of limited resources. Their considerations include historical run times, ridership trends, school bell schedules, traffic conditions, construction projects and the potential for any number of “unknowns."

The work they do is intricate, often with near-surgical precision—planners add a half-minute to a trip here, shave a half-minute there—all applied in massive schedule updates that occur every few months. Analysis of massive quantities of data collected by buses using GPS devices, passenger counters and more is done.

Although our bus schedules are created with a bit of room for expected delays and service impacts, unusual and unexpected delays out of our control still occur. When a big delay happens, it can snowball quickly, resulting in big gaps and bus bunching, particularly on high-frequency routes. Very often, high-frequency routes service streets that host high volumes of vehicular traffic.

We’ll try to explain how and why these things happen, and what we do to minimize it, and why it’s not something that can easily be altogether prevented. 


Why do big gaps form and buses bunch up?

Bunching is frustrating. It frustrates us too, both as people who work very hard to deliver a good service, and also as bus riders, ourselves.

Bunching is the bane of bus systems around the world (it's not just something that happens in Chicago) and, unfortunately, there's no easy fix to it. The phenomenon is an especially difficult challenge for transit agencies who operate service on busy streets with heavy traffic and where frequent service is required.

How does bunching happen? Here’s just one scenario:

Imagine a busy route that has buses running about every 5 minutes on a busy route during the morning rush.

Everything's great until a large truck backing into a dock blocks the street for a bit, delaying a bus just 2 ½ minutes.

But it's just a couple of minutes, right?

Unfortunately, this seemingly minor delay actually amounts to a 50% increase in the space between that bus and the one ahead of it. Assuming a pretty steady flow of people approaching stops along this route, this can mean 50% more people are now waiting to board the bus at the stops up ahead.

At this point, the bus is probably more likely to have to make a stop at every block. It does not just because it has to pick people up, but also because, with more people on the bus, it's more likely someone needs to get off the bus at every upcoming stop. When the aisles get crowded, it takes even longer for a bus to make stops since it people need to make their way through--resulting in what we call "increased dwell times."

All of these factors can lead to the bus falling further and further behind schedule.

Meanwhile, that bus’s “follower” (the bus behind it), starts to catch up.

Even if its follower has a similar delay, it's able to keep a good pace since, with the bus in front of it having served its stops more recently than it was scheduled to, fewer people are now getting on or off that bus at the stops ahead of it. This second bus might not have to stop at every block, its dwell time at each stop stays short and it is able to just breeze right along the street.

In fact, the driver might even need to slow down or stand for a bit to keep from getting ahead of schedule (one of the things that we can and do control, to avoid a bus leaving a gap behind it, which can then create a bunch later).

Despite this following driver doing a good job of staying on-time, she still catches up to her leader and a bunch is formed.

Just that quickly, a "bunch" of two buses come together, each stop has a handful of people waiting at it and the two buses start to leapfrog each other to clear stops as quickly as possible. Of course, this also means a 10-minute gap in service, even though both buses left right on time and started out being exactly five minutes apart.

Both then try to serve the crowded stops ahead in a complementary fashion, but with people on both buses needing to exit at pretty much every stop, they don't really get ahead and both end up getting caught at the same traffic signals, together falling further behind. If it gets bad enough, even a third bus can catch up!

...All because of an unavoidable delay of just a couple of minutes!

At the end of the line, the terminal may “absorb” the delay because some time for a "layover" can be scheduled at the end of a trip. But, if they end up falling too far behind, a gap can even ripple back into the spacing of service in the other direction.

This is where our Bus Service Management staff become crucial to minimizing delays and inconveniences: They can use a number of techniques to restore regular service, such as directing the bus to run express or adding a “fill in” run from another route.

See also:

WBEZ (Chicago Public Radio) did a story on bus bunching and why it happens (and how it’s virtually impossible for any large bus system to eliminate it completely). You can read the story here, and check out this handy animation they made, explaining it:


So what can we do to address a bunch, or prevent them in the first place?

The answers aren't always easy, but we do have a number of tools in our toolkit to mitigate unavoidable delays. Here are some examples:

  • Run "express": We can try to have one or more of the buses caught in a “bunch” run non-stop to get further ahead.

    However, this is inconvenient and frustrating for people who've already been waiting a long time at stops only to see an approaching bus go right past them (especially if the bus is not full).

    This strategy can also be a problem for people already on the bus who need to get off in the area that is being bypassed. To accommodate those riders, an additional delay can then occur as bus officials coordinate letting passengers off to switch to a second bus.

    Because of the potential for added inconvenience and frustration for riders, we try to use this option minimally.

  • "Short turns": In some circumstances, we can do what's called "short turning" a bus, which means having a bus that's mid-route end its trip early, turning back the other way short of the end of the route.

    This restoration technique is difficult to implement, though, as it may require special coordination to ensure that riders exiting the first bus have another bus immediately there to pick them up—and it can only be done if the bus behind it can accommodate all the people from the first bus.

    Side note: When you see a bus not going all the way to the end of a route, it's not always from a delay--it is also a scheduled behavior on some routes, to provide higher frequency along busier parts of a route.

  • As a preventative measure, we do schedule in extra wiggle-room to allow for run-of-the-mill delays. However, this extra time increases the length of each trip, so we also have to be careful not to add too much. Excess wiggle-room can create gaps, crowding and bunching behind a bus, and can also cost money in wasted man-hours. Thus, our schedulers work with care and precision to try and find the right balance.

  • As another preventative measure, scheduling more service can be an option that helps against the likelihood that a delay becomes compounded by crowding and longer dwell times. But we also have to be careful not to spend money on excess capacity in one place at the expense of somewhere else that really needs it.

Suffice it to say, there really isn't a silver bullet for solving bus bunching and it's a problem that affects every busy bus system around the world. Corrective actions can be complicated and need a lot of people and pieces to come together in just the right way to really break up a bunch.

But we continue to work to improve service and regularly work to find new ways to prevent things like bunching, including evaluating new technology and implementing strategies to address it.

However, our buses remain hostage to street traffic accidents and problems as much as individual motorists, and with far less flexibility to adjust routes and stops since people depend on service following the same patterns.


Why did my bus go down the street slowly and/or purposely miss a green light?

We understand how frustrating this is, but this is a necessary evil in the big-picture of how to operate the best possible service. Here are the basics:

In the event that everything lines up in such a way that traffic is lighter than normal, and no events delay a bus, buses can get ahead of schedule because there’s always some wiggle room built-in to anticipate potential delays and variability.

We refer to being early as "running hot."

The problem is that if a bus "runs hot," it creates some problems:

During off-peak hours, running hot can cause a person trying to catch a specific bus to miss it, and then have to wait a full scheduled wait, plus the amount time they arrived at the stop early.

During higher-frequency service, a larger-than-normal gap behind a bus that's running hot leads to the following bus having more passengers than usual, slowing it down and potentially leading to a bus bunch behind it.

Either way, being ahead of schedule creates a gap in service and, potentially, one that’ll lead to bus bunching by increasing the number of people getting on and off the bus behind it, causing it to take longer and longer at each stop.

Since being early is one of few variables that can cause big inconveniences and is a variable that we can completely control and avoid, it’s in our procedures to simply not "run hot."

While it may be frustrating, keeping with the schedule, and not getting ahead of it, is an important, strategic procedure that helps us make the system more reliable, in general.


Some additional thoughts

Delays on high-frequency services like ours are a problem that every major bus and train system in the world faces. As much as we'd love to be able to, it’s simply not possible to account for every variable, and the solutions to when inevitable delays occur are not always easy—though we do try to do everything we can. We want you to know that we are very aware of how delays can affect your day and we experience them ourselves as transit riders who appreciate and believe in what we do. Providing a good service that improves your quality of life is a passion for us, and we think about how to find creative solutions to problems and, in general, how we can do better all the time.

While a good trip, generally, is a trip you don’t notice (you get on, you go, you get to where you’re going), we also know that it’s those bad ones that stand out. But for every time you experience a delay, there are probably a dozen delays that were averted or alleviated because of talented people in the field working hard to keep you on the move (in addition to all those times where things just worked the way they should in the first place). Usually, when a train breaks down, we have it back up and running in just a few minutes and only a small percentage of our buses actually are arriving at stops within a minute of another—but we know those are the things you might be more likely to remember.

Overall, we understand how important a role we play in Chicago being the bustling, busy and exciting city and metropolis it is.

To understand the quality of our service and look for opportunities to make it even better, we extensively monitor and keep track of our performance and quality of service, are constantly responding to delays that crop up—and often to the extent that you might not realize a delay ever occurred. We also recognize our responsibility to always be working to both provide a better service, and work to give you tools to find the best way to go, such as Bus Tracker and Train Tracker.

As always, we welcome feedback, which we regularly use to improve service.  You can reach us via phone (1-888-YOUR-CTA), e-mail or social media (@cta on Twitter,

Further, please feel free to check out our Performance Metrics to see how we’re doing—and also the App Center to find some of the nifty things the community has put together with data we publish about our system.

System status snapshot
‘L’ route status
Blue Line
Normal Service
Brown Line
Normal Service
Green Line
Normal Service
Orange Line
Normal Service
Pink Line
Normal Service
Purple Line
Normal Service
Yellow Line
Normal Service
Bus routes w/alerts
Elevator alerts