Redeye‘s Tracy Swartz – one of the city’s best writers on the transportation beat outside of Streetsblog Chicago, to whom you should still give money – has an interesting article about why people choose to remain on transit (or not) while gas prices plummet. There are actually some interesting lessons in that part of the article, but I want to focus on this line:

Some CTA riders also don’t have cars to make the switch to driving when gas prices are low. About 16 percent of workers 16 years old and up don’t have access to a car to commute to work, according to U.S. Census Bureau American Community Survey estimates from 2008 and 2012.

Tracy showed me the ACS tables where she got that 16% number. But for the purposes of this article, I think they’re a bit (unintentionally) misleading. They tell us that 84% of Chicago workers live in a household with at least one car – but that’s not the same as being able to use a car to commute.

In my household, for example, there are three adults and one car. According to the Census, that means that all three of us have “access” to a car. But practically, only one can actually drive to work. Some households in a similar situation may be able to carpool, but given job sprawl and service sector work schedules, it’s unlikely that number is super large. (The Census says less than 10% of all workers carpool to work.)

So what’s a better estimate of how many workers can actually use a car to commute? To figure that out, I used this Census table, which gives the number of cars in a household by the number of workers.

First, in households with only one worker, about a quarter (113,000 out of 456,000) have zero cars.

 

Of the 254,000 households with two workers, about 11% (29,000) have no cars, and 38% (97,000) have one car. That translates to 155,000 workers without their own car.¹

Of the 57,000 households with three or more workers, about 9% (5,000) have no cars, 19% (11,000) have one car, and 31% (18,000) have two cars. That translates to at least 55,000 workers without their own car.²

So, altogether, there are at least 113,000 + 155,000 + 55,000 = 323,000 workers who can’t use their own car to drive to work.

The Census also tells us that there are about 1,191,000 workers in all. Which means that 323,000 / 1,191,000 = 27% of Chicago workers do not have their own car to drive to work. That’s a good deal more than 16%.

Incidentally, this also means that a huge number of Chicago’s workers – roughly 39% – live in a household where, even if they themselves drive, their spouse, or child, or parent, or friend, rely on public transit (or in some cases bikes) to get around the city. And that doesn’t include households where a high school or college student relies on transit to get to class.

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¹ There are two carless workers for each zero-car household, and 29,000 * 2 = 58,000. There is one carless worker for each one-car household, so 97,000. And 58,000 + 97,000 = 155,000.

² There are three carless workers for each zero-car household, and 5,000 * 3 = 15,000. There are two carless workers for each one-car household, and 11,000 * 2 = 22,000. If each two-car household has three workers, then there’s one carless worker for each of those. (If there are more than three workers, then there’s more than one carless worker – but let’s be conservative.) So that’s 18,000. And 15,000 + 22,000 + 18,000 = 55,000.