Category Archives: Futurism

Ridership projections reveal tricky calculus for transit planners | strib

I get quoted in the Strib by Eric Roper:  Ridership projections reveal tricky calculus for transit planners (though I wish he would clean up my conversational  speech so it looked better on paper. This is why interviews should be by email). Also he used “calculus” in an article.

Prof. David Levinson, a transportation expert at the University of Minnesota, said there is a valid reason for the conservative projections.

“All the forecasts that were done in the 70s, and 80s and 90s…most of them overestimated transit ridership,” Levinson said. “The forecasts that have been done since the new rules have been implemented have gotten much closer to expected ridership numbers.”

That helps federal funders, he said, but also creates some confusion about what exactly the forecasts represent.

“To call that the forecast means that everything will exceed forecast if there’s any economic development affects whatsoever, because you’re not accounting for any of them [economic development effects] or very little of them when you’re doing this,” Levinson said.

It stands in contrast to the city’s projections for a Nicollet-Central streetcar line, Levinson said, which has been sold as an economic development tool.

“I would claim that the streetcar forecasts are more in the line of advocacy forecasting. They were trying to get people to buy into the idea of this,” Levinson said, noting that they would likely have to be adjusted if the project advances in a quest for federal funding.

The forecasts may be about to change, however. John Welbes, a spokesman for the Southwest project, said new ridership estimates will be released between mid-August and early September.

The Futurist Fallacy

As I occasionally write about the future in this blog, I try to keep in mind what I will call “The Futurist Fallacy” –   In the future, everyone will live and behave like  the futurist does today.

Contrast this with William Gibson’s quote: “The future is already here — it’s just not very evenly distributed”, which he is reported to have first said this in an interview on Fresh Air, NPR (31 August 1993).

Both of these may hold provided that the futurist is not in fact behaving the way future will turn out. Of course every good futurist will try to behave in a future-oriented way, trying to be cutting edge with technologies and lifestyles. Many of those will however turn out to be techno-evolutionary dead ends.



Imagine: A World Where Nobody Owns Their Own Car – Eric Jaffe – The Atlantic Cities

Eric Jaffe at Atlantic Cities writes: Imagine: A World Where Nobody Owns Their Own Car :

“Skeptics have also charged that autonomous cars will disrupt any city-based travel models, since people freed from the need to drive will move even farther away from the core. That might be true for people who own their autonomous cars, says University of Minnesota transport scholar David Levinson, but a strong sharing system could promote the opposite movement. “If you’re paying for the car by the minute, then you’re not going to want to move farther out,” says Levinson. “You’re going to want to move closer in.”

Levinson says SAV service that offers convenient on-demand trips gives people a much greater incentive to rely on that system — and a much smaller incentive to take the unnecessary trips often made by private cars. It’s a recipe for the type of multi-modal lifestyle change only possible right now in places like Manhattan. Transit for essential daily trips, cabs (or other alternatives based on the type of trip) for the rest.”

The big market question is when this world will begin to emerge. Levinson subscribes to a timeline in which autonomous cars enter the luxury market in 2020, the technology trickles down into the affordable mid-level range over the next several years, and by 2030 every [edit: NEW] car on the road is driverless. (Other cars would be banned a decade later.) Since car- and ride-sharing operations tend to rely on smaller cars, that would peg SAV networks closer to 2030 — about 16 years from now.

“It’s not that far away anymore,” says Levinson. “But 16 years ago was 1998, and Google hadn’t been invented. So it’s a short time and it’s a long time.”

Structural errors in forecasting

Forecasting is notoriously bad.

S-Curve and the Danger of Extrapolation (from The Transportation Experience, Second Edition, (Garrison and Levinson (2014)).
S-Curve and the Danger of Extrapolation (from The Transportation Experience, Second Edition, (Garrison and Levinson (2014)).

There are many reasons for this, but one is structural, failure to understand the life-cycle dynamics.  The reason for overshoot and undershoot can be understood by visiting the S-curve. Assumed forecasts are made by extrapolating previous results, which is how many businesses and investors and government agencies operate, as shown in the figure. In early years (Birthing and Early Growth) the rate of growth each year is greater than the previous year. Someone extrapolating from history will undershoot actual growth. But in late growth and maturity, growth is slower than the previous year. Someone extrapolating from history will overshoot actual growth.

Extrapolation models are common in transportation, see e.g. Angie Schmitt’s Transpo Agencies Are Terrible at Predicting Traffic Levels. These are used for statewide modeling in many places. Such forecasting methods (assume growth continues at a fixed percent) is embedded in some textbooks, especially for instance, in pavement design.

Combined traffic projections from state and regional transportation agencies (the colored lines) have been wildly off the mark (the black line shows real traffic levels) for more than a decade. Image: SSTI
Combined traffic projections from state and regional transportation agencies (the colored lines) have been wildly off the mark (the black line shows real traffic levels) for more than a decade. Image: SSTI

Urban transportation planning models are better in some ways, in that they include multiple factors. Unfortunately, these models are based on rates at a single point in time. Thus they assume the function that describes the behavior is fixed, only exogenous (input) factors such as demographics, land use, networks, and policies are allowed to vary. Even when multiple years of data are available, such models are typically only estimated on the most recent survey, rather than on trends or changes. The underlying behavior is not permitted to change, only what it responds to. Yet we now have evidence that some underlying preferences do change over time. It’s not simply a matter of getting the demographics or incomes correct. For instance from the 1960s to the 1990s female labor force participation increased. Thus the number of work trips and non-work trips (substituting out-of-home for in-home production) both increased in that period. But that increase has played itself out. Thus the increases it was associated with have peaked. This reflected changing preferences. While hindsight is 20/20, I don’t know if underlying preferences can be modeled accurately prospectively (I am doubtful), but I do know failure to account for them will lead to model inaccuracies.

What changes are going on now that are not considered in travel demand forecasting? A brief (and very incomplete) list below:

  • Vehicle technology shifts (driverless vehicles)
  • Preference shifts among young travelers
  • Changing driver licensing requirements
  • Vehicle ownership vs on-demand vehicle rental (car “sharing”)
  • Telecommunication increasing substitution for work, shop, and social travel
  • Telecommunication complementarity for work, shop, and social travel

None of this is easy to model, certainly not within the existing framework of urban transportation planning models, even more modern activity-based models. In many ways it is easier to do macroscopic than microscopic forecasting. The question is, if some kinds of forecasting are impossible (I can forecast traffic pretty accurately two weeks from today, but not the first Tuesday of 2044), why do we do it? Is there a human-need to fill the void of future uncertainty with authoritative assertions?

Speculating about the future is useful, it opens up pathways. Developing scenarios is useful, it challenges assumptions. Thinking about the lifecycle process and markets helps frame the possible, the plausible, and the likely. Studying history (and past forecasting methods and errors) provides but humility and insight. Visions (and alternative competing visions) help establish what we want. Developing a communal hallucination can organize individual activities to become the ideal (or nightmarish) self-fulfilling or self-negating forecast.  Planning needs more methods for thinking about the future than single point forecasting.

The end of traffic in America: A Q&A with transportation expert David Levinson

A transcript of my podcast with Jim Pethokoukis is now up: The end of traffic in America: A Q&A with transportation expert David Levinson.

By the year 2030, most Americans may only head into the office a few days a week, lots of urban skyscrapers will have been converted into apartments, suburban land prices will have declined, and we’ll be “driving” — or at least sitting in autonomous cars — way less. Goodbye to traffic congestion.

That’s a bit of the possible future sketched out in a recent blog post – “What happened to traffic?”– by transportation expert David Levinson of the University of Minnesota and author of the Transportationist blog. I chatted with Prof. Levinson about his fascinating speculation for my Ricochet Money & Politics podcast.

The End of Driving — Money and Politics Podcast

My podcast on the Ricochet Podcast: Money and Politics with Jim Pethokoukis: Episode 21: The End of Driving is now up

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It’s not just driverless cars. In the latest Ricochet Money & Politics podcast, economist, transportation expert, and blogger David Levinsonargues traffic is declining and will continue to decline dramatically in the coming decades. And that decline is not only the result of some deeper economic and technological trends, but will itself cause a radical restructuring of American society.

What happened to traffic? — The Transportationist