A single wacko month explains half of the last eight years of bus ridership declines

It’s a problem: CTA bus ridership is down—close to 20 percent between 2008 and 2016, even as rail ridership has increased by roughly the same amount.

I’ve written about this issue before, both in the context of the serious service cuts CTA buses (and others) have suffered over this time period, and more recently about the curious, and little-reported, shift in how people pay for rides on the CTA, and how that shift might explain part of the ridership decline.


But in this post, I’m going to present evidence that what might seem like a gradual, death-by-attrition sort of problem is actually largely accounted for by a completely inexplicable one-time ridership crash. In fact, two-thirds of the last five years’ worth of decline took place in a single monthfor no apparent reason, and in a way that’s totally incongruous with the ridership patterns that followed and preceded it.

Why wasn’t this already obvious? Well, it can be harder than you think to get a straightforward read on ridership trends. One big reason is that there are strong seasonal patterns—so, for example, ridership is generally lower in the summer, when high school is out. In the chart of CTA ridership below, you can see clear up-and-downs that repeat every year.


So when the CTA or other agencies report monthly ridership changes, they don’t compare rides in one month to the previous month—otherwise you would just be getting seasonal trends, masking the “real” shifts. Instead, they compare ridership to the same month in the previous year. They also adjust for the number of weekdays and weekends, to make things really apples-to-apples.

That means that in some ways, it’s easiest to see trends in ridership not by charting the actual number of people who ride each month, but by charting these monthly year-over-year changes. If “real” ridership is unchanged, the first chart will still show seasonal ups and downs, but the second will just be flat.

So that’s what I’ve done below: Made a chart of the monthly year-over-year ridership changes on CTA buses and the L.


There are three things to notice here. The first is that monthly ridership trends for buses and the L tend to track each other: When the rail ridership line goes up, the bus ridership line usually also goes up, and vice versa.

The second thing is that rail ridership generally does better than bus ridership, and by roughly the same amount every month—with one big exception, which we will get to in a moment. If you take out that big exception—which, again, just a sec—then between 2011 and 2016, L ridership consistently grew about three percentage points faster than bus ridership. So if L ridership grew five percent in a given month, bus ridership probably grew about two percent; if L ridership grew by two percent, bus ridership probably fell by one percent.

We can think of that three-percentage-point gap (illustrated by the red line in the chart below) as representing the big, long-term, structural reasons that ridership changes: more Loop jobs and destinations, and white-collar workers in North Side neighborhoods with L access, means more train rides; outer neighborhood population decline, service reductions, and perhaps the rise of companies like Uber, mean weaker bus performance. From month to month, other things might happen—a particularly brutal winter could push ridership down, say—but against the background of these structural forces, which will tend to keep rail and bus ridership trends in similar positions relative to each other.


Which brings us to the Big Exception. In September 2013, the gap between rail and bus ridership growth was 2.0 percentage points; in October, it was 4.3 points; and then in November, it skyrocketed to 11.6 points. It then stayed at extremely high levels—on average, 13.7 points—for exactly twelve months, before abruptly returning to its previous three-point average.

What does that mean? It means that in a single month—November 2013—bus ridership cratered ten percent below where we would have expected it, before mysteriously leveling out again at that lower point in the very next month, and then continuing on its previous path of modestly underperforming L ridership trends. I say it cratered by ten percent because the bus-rail gap averaged 13.7 points, rather than three. And I say it happened in just one month because a one-time change will show up in year-over-year comparisons for exactly twelve months, until the prior year’s comparison month includes the change. That is, until you’ve gone all the way around the calendar, each new month is the first time you’ve measured that month at the new, lower level, so it shows up as a year-over-year decline, even though the only real change happened in the first month.

If that doesn’t compute, don’t worry, because the next chart hopefully explains the situation in a more intuitive way. It has two lines. The red line shows actual monthly bus ridership, in millions of rides. The blue line shows what would have happened i bus ridership had perfectly followed the “three percent” rule since January 2011, growing exactly three percentage points more slowly than L ridership.


As you can see, before November 2013, actual ridership behaved almost exactly like the ridership we projected using the “three percent” rule. In fact, in many places, the projected numbers track the real ones so closely that the lines are on top of each other. But then, in November 2013, they sharply diverge. If bus ridership had continued to follow the “three percent” rule, we would have expected about 25.4 million bus rides that month; instead, we got about 23.2 million—nearly ten percent less.

And that gap—after appearing suddenly in a single month—then holds roughly steady thereafter. In other words, again: Since 2011, CTA bus ridership has followed a predictable pattern, modestly underperforming L ridership—except for just one month, when a couple million rides per month suddenly disappeared and didn’t come back.


How big a deal is November 2013? Well, since 2011, annual bus ridership has fallen by nearly 46 million rides, or about 15 percent. Based on the projections above, November 2013 explains fully 30 million of those rides, or essentially two-thirds of the entire decline over the last five years.

And even if you go back to 2008—which includes ridership hits from the aftermath of the recession and the 2010 service cuts—November 2013 explains roughly half of the entire decline.

So what the hell happened? In short: I have no idea. That year, 2013, saw serious fare hikes, as I’ve written about, but they took place in January, 11 months before. That was also the year that Ventra was introduced—but the first Ventra cards became available in August, and the old fare payment system wasn’t put offline until halfway through 2014. There was a Ventra system crash on November 13, 2013, but the CTA estimated that they gave just 15,000 free rides that day—nowhere near enough to explain that month’s ridership crash, and no help at all in explaining why ridership would remain so much lower in subsequent months even after the crash had been fixed.

I will say that intuitively, I can’t imagine what sort of event—especially one that’s low-profile enough not to be obvious—would cause a one-time, seemingly permanent drop of 70,000 to 80,000 rides per day, essentially overnight, with no signs of unusual ridership patterns before or after. That leads me to suspect—though, again, without anything more than circumstantial evidence—that what we’re looking at is actually a measurement issue, rather than a ridership one. But what kind of measurement issue? I don’t know.

This post is long and convoluted enough, but for the sake of transparency I should note that the “three-percent” rule appears to mostly apply between 2011 and 2016 (and possibly beyond). From 2008 to 2010, the recession and harsh service cuts appeared to create a few other waves of difference, which mostly disadvantaged buses relative to rail.

15 thoughts on “A single wacko month explains half of the last eight years of bus ridership declines

  1. Im just fishing here too, and I can’t imagine an economic event that would cause that large a drop but perhaps you explore layoffs, or employment numbers from that month? If indeed it was actual drop and not a measurement challenge maybe a bunch of people lost their jobs all at once?!?
    Thanks for the good work.

  2. I suspect you’re right that there was a change in measurement. I also suspect it may have had something to do with a change in leadership at the CTA. The commissioner at the time stepped down in November 2013. I wonder if he was falsifying ridership (or maybe just incorrectly reporting it), possibly to gain an advantage for funding purposes (just a guess). This Trib article states he left for an opportunity in the private sector. I wonder if his bogus reporting was found out internally and he was quietly “asked” to step down…


    1. CDOT and CTA are different agencies, though–Klein wouldn’t have had anything to do, I don’t think, with CTA’s ridership analysis or reporting.

  3. Could this be the red line south reconstruction ending? Several months of artificially high bus ridership for red line replacement, plus a more attractive rail option for residents from that point forward.

  4. I’ll bite. Yeah Ventra. Ventra on the bus is marginally slower than on the el. That’s not exactly the problem but an indicator of difference between el counts and bus counts, And then there is the human interface on the bus that does not exist at the el.

    At the start of a new system there will be a lot of confusion. I say drivers were waving problems through. And still are. Much fewer problems than at the start of Ventra but still there. If I get on the bus at el speed and it doesn’t register exactly right and the driver says nothing I just keep going. And since the el to bus transfer is sometimes free anyway, or cheap, who really cares that I didn’t get counted. Just people like you it seems. 🙂

    In My Humble Opinion

  5. Red Line Dan Ryan construction ended Oct2013 and replacement bus shuttles were taken off service and the 50 cent south side bus discount went away.

    1. The Dan Ryan construction doesn’t explain why there’s a sudden jump in November 2013; if that were the culprit, the outliers should be May-October 2013, when the Red Line was out of service, with a return to normalcy in November.

  6. I’ve been appreciating your investigation of this mystery and it also seems to me that the evidence presented here would usually point to a possible measurement change. Do we know much about the CTA’s ridership count methodology?

    I think the best argument against a measurement change, though, is that the other explanations you’ve offered in recent months already seem to explain this trend pretty well. The huge behavioral shift from passes to single-rides was presumably primed by the recession service cuts and the early 2013 fare changes and then triggered as people shifted to Ventra. That would seem to have the effect described here: many thousands of riders suddenly faced a marginal cost per transit trip. Every time each of them applied that calculation to a new trip, a certain percentage of them decided differently than they would have before, and that created a new, steady leak in bus ridership.

    (Obviously there’s also a lot of churn in the CTA-riding population, so some of this behavioral shift is actually coming from turnover rather than individuals changing their habits, but it all looks the same in the stats.)

    Another thought: the ACS has Chicago’s bike-commute rate growing quite steadily since 2009, I wonder if that could also be what happened to some of these bus trips, to work and otherwise. If you’re a Chicagoan with no car who needs to travel in directions the L won’t take you, seems like a bike would be the closest substitute to a bus. Especially if you’re extremely sensitive to marginal costs. (Which is to say, maybe we can pin this on Klein after all… 🙂

    1. Thanks for the thoughts! I think the problem with my other explanations (which I still think are relevant for the more normal-looking decline of 5% over the last few years if you take out Nov. 2013) is that the timing doesn’t make any sense. The fare hikes and service cuts took place in January, 11 months before; even if you wouldn’t expect to see all the decline right away, you wouldn’t expect a very slow decline for nearly a full year, and then a sudden delayed crash. Or at least I can’t think of why that would be. And if Ventra was the more proximate cause, then why not in August, when it was introduced, or in 2014, when the old fare payment system was discontinued?

      I think the next step–because I’m truly obsessed–is to use CTA’s daily ridership numbers by line and comb through maybe Sept.-Dec. 2013 to see if I can pinpoint the day(s), and the lines, where the sudden decline happened. If it’s purely methodological, then it’s possible that the whole 10% drop literally happened on a single day.

      Or maybe someone with more knowledge than me will be able to tell me before I do that!

  7. Ventra frequently didn’t work very well on busses the first few months it was implemented, and more often than not the bus drivers just waved everyone past to get on rather than take 10 minutes at every bus stop for passengers’ cards to register the transactions. I suspect that has a lot to do with the reduced ridership count.

  8. If November 2013 is a downward fluxuation, then low ridership in December and January could be explained by ‘Chiberia’. Metra’s issues with switches made a lot of news at the time, and may have reinforced a negative narrative in customer’s minds about any bus reliability issues due to cold and snow.

    1. It doesn’t make sense that the lower levels would remain afterwards, though–and in any case, Chiberia didn’t start in November, which is when the ridership drop is.

  9. One way I’ve seen transit agencies develop ridership numbers is through tracking cash flows. Depending on technology, not all buses in a fleet will be outfitted with counting equipment (which has it’s own inaccuracies). But all of the money needs to be accounted for very regularly. Individual routes can still be studied directly, but the top line number may be from the farebox.

    The problem, obviously, is that a lot of riders – particularly regular riders – use passes, so there needs to be a factor to convert them. As a fake example, let’s say a single fare is $1. A monthly pass might cost $18, on the theory that most regular users commute to work five days a week for four weeks a month so $18 is a bit of a deal on a pass; a lot of these regular commuters probably won’t buy a pass if it’s $25, for example.

    However, from a counting perspective, pass users need to be counted. There’s not necessarily a lot of standards on how many rides a pass user makes, since both transit use and fare structure vary between agencies.

    I’ve seen surveys used, but people tend to overestimate their transit use – especially in more general terms. The $18 pass in the example could be used 30 or 25 or 20 or even 17 times on average (I’ve bought a pass at the start of a month and then gotten sick, for example). There is also an incentive for transit agencies to use a higher number rather than a lower number and to keep an old number rather than regularly revise it.

    I have no knowledge of how CTA ridership numbers are developed, but adjusting an inflated multiplier down as a one-time correction is consistent with the ridership report trends you describe. (The multiplier still being a little high is also consistent with ridership dropping as fewer people use passes.)

  10. I wonder if the city stopped counting certain rides at that time? Maybe free tickets to a sports game, or did the start counting journeys instead of boardings?

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