There are many players in the world of transport policy these days. On net, this influx of new actors into the policy, advocacy and planning realms is likely a benefit, but does offer some concerns. One thing that I see again and again is that new entrants and existing players in the world of urban transport policy too often don’t know or have forgotten lessons learned in the past. On one level this is just a nuisance, and it is good that old knowledge is rediscovered. On another more troubling level this is like health professionals having to rediscover penicillin every other generation.

Here are two recent examples where existing knowledge is ignored or not known or marginalized.

In a recent Vox piece the concept of induced demand was discussed with reference to recent empirical work by the economists Gilles Duranton and Matthew Turner (a few months ago Wired also wrote about this particular work.). Induced demand is a well-known concept that goes back at least to Anthony Downs’ “Iron Law of Congestion,” [and was discussed informally by Lewis Mumford (in 1955), who was referring to Mitchell and Rapkin’s Urban Traffic: A Function of Land Use (1954)] yet the Vox piece suggests induced demand is new knowledge. Reading beyond recent urban economics research reveals that scholars in transportation economics and urban planning have extensively explored induced demand. Here is a 1995 article by Mark Hansen in ACCESS where he describes the problem. Robert Cervero, Robert Noland, Robert Cervero and Mark Hansen and the Transportationist himself (note to regular readers: this post is by David King, not David Levinson) are some of the scholars who have published in leading journals, presented at conferences and included induced demand in their teaching. Here is what Robert Cervero wrote in 2000:

“No issue has paralyzed highway programmes and side-tracked our ability to rationalize new road development as concerns over “induced travel demand”. Time and again, experiences show that building new roads or widening existing ones, especially in fast growing areas, provides only ephemeral relief – in short time, they are once again filled to capacity. A study using 18 years of data from 14 California metropolitan areas found every 10 percent increase in highway lane-miles was associated with a 9 percent increase in vehicle-miles-traveled four years after road expansion, controlling for other factors. Similar findings have been recorded in the United Kingdom. In the United States, regional transportation plans, such as in the San Francisco Bay Area, have been legally contested by environmental interest groups on the very grounds that they failed to account for the induced travel demand effects of road investments and expansions.”

This ACCESS article (2003) by Cervero is worth reading for nuance about what induced demand really means for transport planning and policy. He notes that while induced demand claims have stopped highway expansions in the past, induced demand claims gloss over more important concerns about the use and costs of travel.

It is also worth noting that even though induced demand is usually discussed in the context of expanded road capacity induced demand actually applies for any particular transportation technology. Transit expansion along a corridor has the same effect on induced demand as road widening. On his blog Kevin Krizek explained how congestion is a poor argument for expanded cycling facilities also because of induced demand. We actually know a lot about how transport capacity affects the price of travel, which affects demand for travel across time and space.

A second example about forgotten knowledge has to do with taxi policy. In a recent opinion piece about how wonderful Uber is Mohamed El-Erian describes how Uber will disrupt the inefficient taxi stands near Penn Station in Midtown Manhattan:

“Arriving earlier this week in New York at Penn Station, I joined many others in a rather slow-moving line for taxis. I did so out of habit. But a few minutes into my wait, I realized that the smart thing to do was to pull up the Uber app on my phone. In a few seconds, Uber linked me up with a car, which picked me up four minutes later. The driver was courteous, and the vehicle was clean. And all this for a fare that was similar to what I would have paid for a traditional cab — after a much longer wait, that is.”

This is a terrible argument for Uber type services and reflects little understanding about how taxi networks actually work on existing streets. The whole reason we have taxi stands is because it is really inefficient to have hundreds of people emerge from Penn Station (or any event, station, airport, etc.) to hail hundreds of cabs. We do not have the street capacity or curb capacity to accommodate this, and some type of queuing is necessary. The Uber model, as described, only works when a few people are using the service and is simply not scalable to the extent that a taxi queue is.

These are just two examples, but lots of people are wading into transport policy based on limited reading and personal anecdotes, and if we follow their lead we will have to relearn all the things that we already know. Forgetting knowledge is not a new phenomenon and not limited to any particular set of experts, but it is problematic and deserves more discussion about how to fix it. In a recent lead editorial in the May 2014 Planning Magazine (gated link) the American Planning Association’s CEO, Paul Farmer, begins as follows:

“During a chat about planning in the U.S. and Canada, several planning colleagues addressed the topic of value capture. “We’ve coined the phrase ‘windfalls,’” one Canadian colleague proudly remarked in describing the unearthed benefits that a property owner might realize from investment made by others. The late Don Hagman might have been pleased, amused, or irritated by this appropriation of the concept he popularized, if not invented, in his extensive writings half a century ago.”

(The book referenced is Windfalls for Wipeouts: Land Value Capture and Compensation.)

Concern about keeping knowledge alive isn’t just sour grapes about all the stuff I learned in grad school that people ignore. It’s not clear how we can steadily move policy forward (in a better way, however “better” is defined) if we can’t keep the lessons of the past in mind. This is not a question only for transport policy, either. In a recent book Jo Guldi and David Armitage argue that historical study should play a larger role in economic and policy debates.

As transport policy attracts more specialists from fields outside of transport—economics, computer science, software engineers, data miners, etc.—the challenge of sharing existing knowledge rather than rediscovering knowledge is really important. We don’t need to have lots of policies that won’t work just to relearn than such policies don’t work.