It's baaaaaaaack: the zombie study that won't die. After a four-year reprieve, the Texas Transportation Institute (TTI) has once again published its infamous Urban Mobility Report. So if you're seeing a spate of headlines about how the traffic is bad and getting worse, coupled with outrageous dollar amounts that Americans supposedly lose to congestion—like $166 billion in 2017—the source of those claims is almost certainly the TTI report.

This report is pure propaganda for the road-building industry, designed to elicit credulous takes from major news outlets that cement in the public's mind the idea that We Need to Spend More On Infrastructure™. It inflates the cost of congestion in a dozen different ways, by making unreasonable assumptions that don't reflect the real world. It has been debunked repeatedly by a range of transportation policy experts, and yet it just. Keeps. Coming. Back. And without addressing any of the substantive criticisms.

If you want to read some of those substantive criticisms, those smarter than I have already done a great job enumerating them. Here are a couple good links:

Glaring problems with the report include that it assigns the value of time lost sitting in traffic based on prevailing wages, which is a nonsensical practice to economists: the alternative to losing 6 minutes on your commute is virtually never that you could have otherwise earned 6 additional minutes of pay at your job. And very rarely would anyone be willing to spend 6 minutes worth of their wages (say, on an express toll lane) to avoid that congestion—turns out this has been studied and people will pay, on average, more like $3 an hour, or well under minimum wage.

Another error: the study defines “delay” (congestion incurring a cost) as any time vehicles are moving less than free-flow speed. But on some roads, the free-flow speed is actually greater than the legal speed limit. Drivers simply obeying the law are counted by the TTI as evidence of congestion.

The glaring errors in the report go uncorrected because correcting them would defeat the report’s purpose, which is to make congestion look bad and always worsening. Because others have done such a thorough job deconstructing the report's definitions and assumptions, though, I'm going to attack it from a more root philosophical angle that helps explain why this report is asking and answering the wrong questions.

The Disastrous Assumption at the Heart of the UMR (and Our Prevailing Transportation Policy): That “Mobility" is Our Goal

It's right there in the title of the report: "mobility." This is assumed to be the goal of our transportation system—to move people. Sounds reasonable and obvious enough.

Accordingly, the way the authors measure traffic congestion is in "delay." This also sounds reasonable on its face: on a congested freeway, you travel more slowly, get to your destination later, and those are minutes lost that you could have spent doing things you value. Ergo, congestion delay is costly for society, according to the TTI.

All of this is intuitive to ordinary people, which is why the TTI has no trouble getting their findings parroted in the press without much critical analysis. The problem with it is that it’s wrong. It ignores how we actually make transportation decisions in the grand scheme of our lives.

The Oxford English Dictionary defines mobility as "the ability to move or be moved freely and easily." Is that ability valuable to us in its own right? Generally no. What we value is the stuff that mobility helps us access. Your job. Your kids' school. Your church. Your doctor. The grocery store. Friends' houses.

We arrange our lives to have as much access as we can manage to the things we value. And we do that with a sort of travel time budget in mind: how much time we're willing to spend in transit in a typical day. It might vary for individuals, or in different contexts, but there's an average range. Few if any of us object to spending 20-30 minutes of our weekday just moving from place to place. That's just life. But virtually none of us wants to spend 3 hours of our weekday just moving from place to place. It's why few people are willing to live in Hartford, CT or Allentown, PA and commute to New York City, even though housing is several times cheaper in those cities.

Mobility is the answer to "How far can you get?" from a given location in a given time. The answer to the question, "What can you get to?" in that time is called accessibility, and is a better way to think about the actual value of transportation.

For decades, we've oriented our transportation spending toward mobility—making it easier for people to travel longer distances at higher speeds. And the results are evident in the contrast between these two graphs: