An excellent recent article on CityLab discusses the important concept of ‘induced demand’ – the phenomenon that extra road capacity encourages more people to drive and fills the road again – while asking the important question of why so much money is still devoted to widening the road when we know it is not working.
For those who do not know the induced demand, this is an extremely important concept in transport planning, known for many decades:
Economist Anthony Downs is often credited with first formulating this “brazen congestion law” in 1962, when construction crews hacked highways through American cities. Downs published a seminal article with a stern warning: “On suburban urban freeways, rush hour traffic jams increase to maximum capacity. In other words, adding more lanes won’t solve the booming traffic; the extra car space inevitably invites more trips, until the traffic jams are as bad as ever.
Not only has the induced demand been known for a long time, but it has also been measured time and time again in many countries, highlighting the futility of trying to solve congestion by building wider roads:
Downs’ Iron Law applies not only to American cities, which are increasingly congested despite billions of dollars in fresh pavement, but also to cities around the world. The expansion of motorways in Norway and Great Britain did not reduce congestion there either. The principle meets today little opposition among economists and town planners. “It’s widely accepted,” says John Caskey, who teaches induced demand in his urban economics course at Swarthmore College. “For economists interested in urban transport, there is no real debate.
And yet billions and billions of dollars continue to be spent on widening roads in the hope that the next road can actually – finally – achieve the desired goal of reducing congestion. Despite somewhat better rhetoric than most recent governments, the current government’s transportation plans are still very much geared towards building roads rather than public transportation, walking and cycling:
Beyond what’s in the NLTP shown above, the government is also injecting billions from general taxation into New Zealand’s upgrade program, which primarily funds new or wider roads like Penlink, Papakura-Drury, Tauranga Northern Link and Otaki north of Levin.
Yet for many, even this vast expenditure on more and wider roads is not enough, despite decades of evidence that more and wider roads will not really help solve congestion. For example, a recent AA newsletter insists on spending even more on this failed strategy:
It is clear that a significant rebalancing of transport program is needed, in the form of a greater focus on improvement of general traffic conditions. This would result expand and advance:
- New road projects on the outskirts of the city (in particular, around high growth areas)
- Targeted widening of sections of the motorway network
- Small adjustments (such as dynamic traffic lights,period cleared roads and reconfiguration of tracks at bottlenecks) all over the network
Reestablishment of Mill Road and second stage of the Papakura in Drury The widening of the southern motorway is essential.
There is no sense in continuing to spend billions of dollars on solutions that have been proven over and over again to be ineffective. So why the hell does this still happen? The article suggests a number of reasons.
First, there is very little accountability in place to properly assess whether past investments have actually achieved what they intended to do, let alone ways in which these lessons are applied to future projects.
Part of the problem is the lack of accountability, says Beth Osborne, director of the transportation advocacy group for America. The federal government does not penalize states that make mistakes in their congestion alleviation estimates, as TxDOT did dramatically with Houston’s Katy Freeway, which in 2011 expanded to 26 lanes at a cost of 2.8. billion dollars, half of which came from federal funds. . The following year, an article in the Houston Chronicle declared the project a success: “What was once a day-long traffic jam is now mostly smooth sailing.”
But in 2014, most rush hour trips on the Katy took even longer than before the expansion.
Federal inaction “keeps TxDOT from finding any induced demand in their project,” Osborne says, “even though their last 25 projects haven’t gone very well because of it. TxDOT’s website currently predicts travel time savings of up to 84% from its $ 7 billion proposal to expand I-45 into Houston, which many residents and local officials are looking to see. oppose. (TxDOT did not respond to a request for comment.)
Matt Hardy, program director for planning and performance management at the American Association of State Highway and Transportation Officials (AASHTO), agrees on the need to look at historical results. “We don’t go back a lot to see if the project has delivered the expected benefits,” he says. “I wish we would. “
Over the past 20 years, huge parts of Auckland’s highway system have been widened – most of the North Highway to Akoranga North, almost all of the Northwest Highway, the South Highway through the spaghetti junction, then from Otahuhu to Papakura (soon Drury). Yet before Covid-19, these highways were more congested than ever. Even massive projects like the Western Ring Route and Waterview Connection, brought relatively short relief and started to fill up again before the most recent closures. But there is no responsibility for this, and even almost no control over the success (or not) of projects. Waka Kotahi even stopped bothering to undertake post-implementation reviews in August of last year.
Second, there is a lot of interest in ignoring the induced demand. In New Zealand, there is a close relationship between motor vehicle and freight lobbies and transport policy makers, which undermines evidence-based public policies.
Entire organizations – the state transportation departments in the United States, Waka Kotahi and to a lesser extent Auckland Transport and other councils in New Zealand – have a huge vested interest in pushing to continue building great roads that encourage driving, which generates more income that can help fund the next generation of projects.
Gasoline taxes further distort decision-making, as the revenues collected often go directly to state transportation departments, as they did 90 years ago. By implication, an initiative that reduces driving (such as an expansion of transit) could result in a lower state DOT budget, while an initiative that induces more driving could result in a bigger one – even if heavier traffic means that the drivers themselves do not benefit from it.
Eric Sundquist advised state DOTs on strategic planning for a decade before recently becoming an advisor to Caltrans, the California State Department of Transportation. “I remember working with a DOT manager in the Midwestern State who showed me his dashboard, which included a measurement of the kilometers driven by vehicles,” says Sundquist. “The objective of the state was clearly more VMT. When I asked why, I was told that more VMT would provide more income to maintain the public system. “
Such an attitude does not surprise Jose Gomez-Ibanez, professor emeritus at Harvard Kennedy School, who has studied transport financing for decades. “States are rewarded for ignoring induced demand,” he says. “There is a lot of self-interest involved.”
Waka Kotahi’s income comes mainly from fuel taxes and road user charges, which literally means that reducing travel and the use of fossil fuels – essential for tackling climate change – is undermining it. funding flow. Even though there are a lot of well-meaning people in Waka Kotahi, it is a very bad incentive structure for an organization that is to play a vital role in transforming our transportation system over the next few years.
Third, and perhaps most importantly, the induced demand is a bit counter-intuitive. It also takes a while to get started, which means the big new project looks like it was initially successful. There are also many hypothetical “counterfactuals” about what could have happened without the project, which are never really possible to know.
“The whole notion of induced demand is a bit counter-intuitive,” says Sundquist. “Building highways seems like a simple thing to do. And it allows cars to go faster – for a little while. “
Caskey agrees. “I understand that if someone driving everywhere sees traffic jams their immediate solution is to keep paving the way. It’s sort of a natural reaction.
This makes the subject of induced demand a challenge for policy makers. “Everyone with a driver’s license thinks they understand transportation,” says Rosenberg. Meanwhile, politically powerful entrepreneurs, unions and automakers are being urged to keep the public confused.
There are positive signs lately that key decision makers understand how the induced demand makes it unnecessary to build new and wider roads to solve congestion. The balance of investment is slowly but steadily shifting towards projects that actually reduce the demand for vehicle travel through the change of fashion, and we’ve actually seen major road projects like Mill Road and East West Link canceled without much public outcry. . Yet in other respects it still seems like we still have a long way to go, especially when it comes to the more ad hoc transport decisions that governments increasingly seem to be making, like the upgrade program. from New Zealand. Despite decades of evidence to the contrary around the world, it seems many people still believe that building more and wider roads will actually solve traffic jams.