Surprising Things You Never Knew About Transport

This is the first in a series of four short films prepared by a faculty team from the Centre for Transport and Society at the University of the West of England (UWE Bristol). The four podcasts pose some interesting questions and give an insightful appraisal of what influences travel habits, delivered by nationally leading experts in the field of transport research: Professor Glenn Lyons, Dr Steve Melia, Professor Graham Parkhurst and Professor John Parkin. Today’s film is presented by Steve Melia and looks into some surprising questions from Steve’s forthcoming book ‘Urban Transport Without the Hot Air’. All four films can be viewed on the UWE Bristol web pages.

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Op-Ed: Why things are not good for UK citizens — and how to make them better

- By John Whitelegg

We are not doing very well in the UK on things that matter to most people.  We are the 6th richest country in the world and yet we come very near the bottom of most rankings on things like child poverty, inequality, pensioner poverty, excess winter deaths, teenage pregnancy, NEETS, percentage of electricity generated from renewables, levels of cycling and quality of public transport.  None of this is necessary and it is safe to assume that local and central government did not set out to achieve these poor quality outcomes.  So what is going on?

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Op-Ed: Do you know your ecological footprint?

Toward the end of each year, I take a few minutes to run my personal Ecological Footprint scan to see if I can get a handle on how I am doing relative to myself, to others and to the planet. Seems like the least I can do, not less because it does oblige me to think about my life pattern and choices in the greater scheme of things. “Walk the talk”, etc., etc. (PS. On a more global basis, to get a feel for where the high scores hang out, this map of earth lights at night will provide you with some good clues.) Continue reading

Sustainable Transport and the Importance of Pattern Recognition

In order to turn around a very big boat that is moving in the wrong direction – think global warming or any of the other wrong-way trips that we are currently locked into when it comes to transport in cities – it helps to be smart, studious and work very hard. But it is if anything even more important to have a feel for what is really going on. And this is where the fine art of pattern recognition comes in. Pattern recognition: all too often the empty chair when it comes to understanding and decision making in the field of transport policy and practice. No wonder we are doing so poorly. Continue reading

To fix Sustainable Transport: Ensure Full Gender Parity in all Decision and Investment Fora (QED)

Today is International Women’s Day. And not only that, 2011 marks the one hundredth anniversary of this great and necessary idea. So what better occasion for World Streets to announce publicly, loudly and yet once again our firm belief that the most important single thing that our society, our nations and our cities could do to increase the fairness and the effectiveness of our transportation arrangements would be to make it a matter of the law that all decisions determining how taxpayer money is invested in the sector should be decided by councils that respect full gender parity. We invite you to join us in this challenge and make it one of the major themes of sustainable transport policy worldwide in 2011. Continue reading

Editorial: The Seven Simple Truths of Sustainable Mobility (Come argue with me)

Sometimes in life things can be simple. Let’s look at one case.

Doubtless the most severe single problem holding us back in the hard up-hill struggle for “sustainable transport” in cities and countries around the world is that so far everyone seems to have a different definition and a different agenda.  Google offered 947,000 entries under this phrase this morning and all it takes is a quick tour of the Google News rubric to  get a quick education on the enormous range of interpretations of what the phrase means to different people, places and interests. Continue reading

Testimony: Science and Technology Select Committee, UK House of Lords

In the last weeks I was asked to provide written testimony and evidence in answer to a “Call for Evidence” for the UK House of Lords Science and Technology Select Committee on the subject of “Behaviour Change —Travel-Mode Choice Interventions to Reduce Car Use in Towns and Cities”. As can happen in these things, in my remarks I moved away from the chosen topic (instruments for behaviour change),  on the grounds that there are other more fundamental issues that need to be tackled first. In the following you will find my submittal of last Monday to the committee, whom I thank for giving me this opportunity to share my views.
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1.4285714285714285714285714285714 e-10

With the world’s population to pass seven billion next year– meaning that my and your fair share of the world’s resources will be on the order of 1.4285714285714285714285714285714e-10 – it is time perhaps to give some consideration as to who “owns” what on this sweltering planet. The very concept of ownership digs very deep into the psyche and the way in which the owned object is used. Let’s take your or my car for example. The odds are that one of us is an owner – and it is well known there is not a single country, a single city on this planet in which the owners of automobiles pay even a small fraction of their total cost to society. What does that mean in this particular case? Continue reading

Sharing: Strategy for a Small Planet

- Keynote address by Eric Britton, Co-Chair of the World Share/Transport Forum, to the first international Share/Transport Conference. Kaohsiung. 16 Sept. 2010

I appreciate this opportunity to share with this distinguished international audience by way of introduction to the presentations and discussions that will now follow a few words on why I think that the concept of more and better sharing of scarce resources of all kinds is an important concept for quality of life for each of us on this small and shrinking planet. And to talk with you as well briefly on why I have come to the conclusion that the transport sector gives us a great place to start both to do a lot more sharing and to learn about why we human beings like, or don’t like, the idea of sharing things. Let’s start with . . . ourselves. Continue reading

What Transportation And Public Health Can Learn From Each Other About Changing Public Behaviors

Which of the following is more likely to get you to drive slower down a street? Or to get the majority of car drivers on that street to slow down?

• A long talk with a friend about the dangers of speeding to yourself and others.
• A newly posted sign announcing a lower speed limit.
• A stop sign placed in the middle of the block.
• A series of speed bumps along the road. Continue reading

Car Free Days 2014: Part 2. Thursday: A breakthrough strategy for reducing car dependence in cities

This is the full unedited text of the original 18 October 1994 presentation to the Ciudades Accesibles Congress in Toledo Spain organized by the Spanish Ministry of Public Works, Transport and the Environment, with the participation of Leber/EcoPlan International, Car Free Cities Initiative of the EuroCities program and the Direction General XI of the Commission of European Communities. Continue reading

Oops! What went wrong with "Old Mobility"

In order what needs to be done to create a healthier and better performing set of transportation arrangements, World Streets make a consistent distinction between what we call “old mobility” and “new mobility.” The difference between the two is quite simple. And substantial.

Old mobility was the form of transportation policy, practice and thinking that took its full shape and momentum starting in the mid twentieth century, at a time when we all lived in a universe that was, or at least seemed to be, boundless and free of constraints. It served us well in many ways at the time, albeit with exceptions, though we were blind to most of them most of the time. It was a very different world back them. But that world is over. And it will never come back.

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New Politics, New Economics and New Mobility : Frugal Transport comes of age in Britain?

John Whitelegg, Editor of World Transport Policy and Practice, offers up a lead editorial in the latest edition of the Journal which was published today and is freely available here. His proposal makes particular economic sense at a time of great economic uncertainty, and of course not only in the UK. His core recommendation: (a) Cancel systematically all public investments that do not pass the sustainability test. What goes? (b) £10 billion for unnecessary road building. (c) £32 billion for uncalled for high speed rail. And (d) elimination of all but a handful of domestic aviation subsidies and investments. And with those frugal savings, the new government team can really go to work to guarantee the sustainable transport agenda.

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No Accident! Traffic and Pedestrians in the Modern City

As most of our regular readers are well aware, World Streets is no friend of speed in cities. To the contrary, it is our firm position that a considerable number of the basic objectives associated with sustainable mobility and sustainable cities can be achieved if we do no more than to reduce top speeds in and around our cities in a strategic and carefully thought-out way. The great technological virtuosity of traffic engineers and technical planners permit us to do this, while at the same time retaining a well working transportation system, a healthier city, and a viable local economy. Listen to what John Rennie Short and Luis Mauricio Pinet-Peralta have to tell us on the subject.
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How to build more traffic? It’s not hard. Read on.

A bit down on the resource column just to your left is an early warning system of sorts which calls up relevant articles from an eclectic collection of independent sources that publish regularly in areas related to our field. One of these is Planetizen, where yesterday we spotted this thoughtful interview we thought you might wish to check out. It’s an old story, but good research helps us to get beyond the purely anecdotal. And now that we know it, the job is to get that message across where it counts.

Freeways Responsible For Emptying Out Cities

- Interview by Tim Halbur, managing editor of Planetizen

A recent study shows that for every significant freeway that gets built in a major city, population declines by about 18%. Nathaniel Baum-Snow, author of the study, talks with Planetizen.

Photo: Nathaniel Baum-SnowNathaniel Baum-Snow is a professor of economics at Brown University. His research has been remarkable consistent and urban-centric since writing his dissertation in 2000 on “The Effects of New Public Projects to Expand Urban Rail Transit.” Baum-Snow’s work came to our attention when he was cited in a recent Boston Globe article quoting his study that concluded that each new federally-funded highway passing through a central city “reduces its population by about 18 percent.” The implication of this type of data-driven evidence of the effect of highway construction on cities is often hard to find, so we went to the source.

BAUM-SNOW: There’s a lot of anecdotal evidence we see out there in metropolitan cities that a lot of jobs exist in the suburbs, and that that wasn’t nearly as true 40 or 50 years from now. But amazingly enough, there’s not a lot of systematic, empirical evidence about the extent of which that employment decentralization has occurred, and their isn’t a lot of empirical evidence about how commutes have changed over time. In the process of writing my first paper about highways and suburbanization, I tried to read everything I could about this and I couldn’t find anybody who’d looked at this in a systematic way across metropolitan areas.

And it turns out that not only has the nature of residential and employment locations have changed dramatically, but the nature of commuting patterns have also changed dramatically. Now, the vast majority of commutes do not involve the central city at all, even commutes made by people who live in metropolitan areas, whereas in 1960, the majority certainly involved central cities either as origins or destinations or both. And that’s a major change. I think the next step is to try to understand all the things that generated that change.

PLANETIZEN: Over the last couple of decades, planners have shifted their attention to thinking about regional planning. It seems to me that your research could indicate that regional planning is unnecessary, because people tend to live and work in their own locality. Is that your take?

BAUM-SNOW: Actually, I think it’s an argument in favor of having more regional land use and transportation planning, and the reason is that if suburb A builds a highway to connect to suburb B, that’s going to effect the distribution of commutes not only between those suburbs but also the commutes in the region as a whole. So there are going to be these externalities where someone in suburb C has a faster way to get to work, so they’re going to start using it and filling up this new highway. And a business downtown might say, hey, there’s this new infrastructure, let’s go locate out there and I can have a lot more space to work with. So anytime one part of a region changes something, it’s going to effect population and employment throughout the metropolitan area. So I think it’s important to engage at the regional level.

I think that zoning and densification are important. But there’s no way to make people or firms locate in a densely packed manner without providing the transportation infrastructure to allow them to do it. So you have to have some sort of policy at the metropolitan area-level. And what you can get is local communities imposing costs on everybody else by doing something like imposing big exclusionary zoning right next to the urban core. And that’s clearly not economically efficient for the region as a whole- they’re obviously trying to protect their housing values. So I think that it’s important for regional government to be proactive and realistic with transportation planning.

Everybody would like to live in a dense neighborhood as long as they have the biggest house on the block. So they have a lot of living space, but their neighbors are all contributing to the sidewalk life. There’s a balance there that is hard to get around, so there is a role for zoning that encourages density and gets the transportation infrastructure set up in a way that is feasible.

Image courtesy of Flickr user jbrownell.

PLANETIZEN: So was the creation of the highway system a good thing overall or a bad thing?

BAUM-SNOW: I do think that there was a welfare benefit from highway construction for a lot of people. People get to live in bigger homes, they have more choice in where they’d like to live. Now most households are dual-worker households, which wasn’t true back in 1950. Highways have allowed two people living in the same house to commute to different areas each day, so I think there’s been a welfare gain from that. So it’s sort of a mixed bag, but I think most people would say that although there have been some costs, the highway system has been a good thing.

A lot of people think that decentralization is about fleeing to the suburbs out of central cities, but if you look at the change in the spatial distribution of the population across large metropolitan areas, you find that it’s really much more of a spatial phenomenon. You see that the population density in the more peripheral regions of central cities actually went up quite a bit over the last 50 years, while the population of the central business districts went down.

PLANETIZEN: And how did you, as an economist, get interested in issues of transportation and land use planning?

BAUM-SNOW: Growing up I’d always been interested in urban transportation. I always loved riding the subway, and one of the first puzzles my parents gave me as a kid was a puzzle map of the United States with all the states and the interstate highways. And I would memorize the subway maps and bus maps, stuff like that. So it was always something I liked.

And as I got older, I would explore different neighborhoods in Boston (where I grew up), and I was fascinated how you could have such heterogeneity in land use patterns and in socio-demographic patterns within such a small space. So in college, I wasn’t sure what I wanted to do, but I had an interest in public policy and politics, and I took a lot of different classes. Economics struck me as a field that had the best hope in helping me think about all of these things in a satisfying way.

# # #

Nathaniel Baum-Snow is an assistant professor of economics at Brown University. You can access his research papers at his website here.

About the author:
Tim Halbur is managing editor of Planetizen, the leading news and information source for the urban planning, design and development community. Tim is the co-author of Planetizen’s Insiders’ Guide to Careers in Urban Planning and Where Things Are, From Near to Far, a book for children about city planners and what they do. He is also an audio producer and artist, collaborating with artists Amy Balkin and Kim Stringfellow on Invisible 5, a self-guided critical audio tour along Interstate 5 between San Francisco and Los Angeles engaging with issues of environmental racism.

It was there all the time: Putting shared transport to work. * Share Transport 2010 – Conference in Kaohsiung, ROC *

The all but invisible (unless you were looking for it) trend behind true sustainability in the transport sector is . . . sharing. We now know that the only way to significantly reduce the CO2 load of our transportation arrangements is through corresponding reductions in motorized traffic (VMT/VKT). Which means efficiently getting more people and goods in those vehicles still plying the road. And to do this well, we need to learn a lot more about sharing.

Kaohsiung 2010 Conference plan in brief

The objective of this International Conference – the first of its kind — is to examine the concept of shared transport (as opposed to individual ownership) from a multi-disciplinary perspective, with a strong international and Chinese-speaking contingent. The goal of this event is to bring together leading thinkers and sharing transport practitioners from around Taiwan, Asia and the world, and to provide them with a high profile opportunity to share experience, perspectives, ideas, and recommendations on this important trend.

The concept of shared transport is at once old and new, formal and informal, and one that is growing very fast. However to now attention has focused on the technical details of each project and approach — as opposed to stepping back first to gain a broader understanding of the basic human, societal, and economic trends and realities behind this kind of behavior more generally.

But something important is clearly going on, and the Kaohsiung event will be looking at this carefully, in the hope of providing a broader strategic base for advancing not just the individual shared modes, but the sustainable transport agenda more broadly

Background: Sharing in the 21st century – Will it shape our cities?

After many decades of a single dominant city-shaping transportation pattern – i.e., for those who could afford it: owning and driving our own cars, trucks, motorcycles and bicycles, getting into taxis by ourselves, riding in streets that are designed for cars and not much else — there is considerable evidence accumulating that we have already entered into a world of new mobility practices that are changing the transportation landscape in many ways. It has to do with sharing, as opposed to outright ownership. But strange to say, this trend seems to have escaped the attention of the policymakers in many of the institutions directly concerned.

Largely ignored by the transport policy establishment perhaps but transport sharing is an important trend, one that is already starting to reshape at least parts of some of our cities. It is a movement at the leading edge of our most successful (and wealthiest and livable) cities — not just a watered down or second-rate transport option for the poor.

With this in view, we are setting out to come together to examine not just the qualities (and limitations) of individual shared mobility modes, but also to put this in the broader context of why people share. And why they do not. And in the process to stretch our minds to consider what is needed to move toward a new environment in which people often share rather than necessarily only doing things on their own when it comes to moving around in our cities worldwide.

As a contribution to international understanding in this fast emerging but largely unexplored field, the city of Kaohsiung is organizing, together with an international team from the Chinese Institute of Transport (CIT), the Global New Mobility Project, Megatrans Taiwan, and National Taiwan University, a three-day international conference and brainstorming session to take place from 16 – 18 September 2010, in which a number of people working at the leading edge of these matters will come together, first to examine together the general concept of sharing in the 21st century. And then, once this broader frame and understanding has been established, go on to consider how sharing as an organizational principle is working out in each of the individual mobility modes which are rapidly gaining force in cities around the world.

Sharing in Transport (Quick introduction)

Below is our latest list of the shared transport modes to be considered by the conference. (This list to be prioritized, pruned and consolidated as useful for the conference. Only selected topics will be covered by the formal sessions.)

1. Bikesharing
2. Carsharing (includes both formal and informal arrangements
3. Fleetsharing
4. Ridesharing (carpools, van pools, hitchhiking – organized and informal).
5. Taxi sharing
6. Shared Parking
7. Truck/van sharing (combined delivery, other)
8. Streetsharing 1 (example: BRT streets shared between buses, cyclists, taxis, emergency vehicles)
9. Streetsharing 2 (streets used by others for other (non-transport) reasons as well.)
10. Public space sharing
11. Work place sharing (neighborhood telework centers; virtual offices; co-workplace; hoteling)
12. Sharing SVS (small vehicle systems: DRT, shuttles, community buses, etc.)
13. Cost sharing
14. Time sharing
15. Successful integration of public transport within a shared transport city? Including bus and rail
16. Team sharing
17. Knowledge-sharing (including this conference)

Initial conference details (to be finalized)

Event: Three day international conference and planning workshops

Dates: 16-18 September 2010.

Theme: “It was there all the time: Putting shared transport to work in our cities”

Location: City of Kaohsiung, Taiwan, ROC

Hosts: City of Kaohsiung, with support of the Chinese Institute of Transport and National Taiwan University

• Presenting the leading edge of thinking, policy and practice in this fast emerging field.
• Panel of distinguished international speakers will be joined by Taiwanese and Chinese leaders

• Researchers, city administration, activists, NGOs, students, media, and suppliers to the sector
• From Taiwan, China, South-East Asia and all other interested

Participant questionnaire:
Each participant is invited to fill out a short questionnaire prior to registration, to help the organizers structure the conference and in particular the breakout sessions on the various share modes to serve the needs of the group better. Comments and suggestions are also welcomed, and the organizers commit to answering your communications and questions.

Call for papers: (To follow.)

Poster sessions invitations: (To follow.)

Other events in planning stages:
There are several other closely related events that are to be integrated into the program. While final details are not yet available, but here are several of the events that are presently under discussion:

1. Integrating the meeting with the 2010 Kaohsiung Car Free Day (the seventh in their series since 2003)
2. Ditto for a New Mobility Week presently under discussions.
3. A possible New Mobility Master Class (again focusing on Kaohsiung)
4. Working links to the Taipei Low Carbon Cities program
5. Kids Sharing Channel (Open school project)
6. University Media project:
7. A guided tour program for visitors taking them to key sharing and new mobility projects and cities in both Taiwan and the PRC.

Language: Chinese/English. Full translation of all sessions

Sponsors: Under discussion. Both private and public sector partners being invited to participate.

Conference venue: Garden Villa Kaohsiung –

Media: The program will be media rich, all the way through from using the latest Web, internet, videoconferencing and virtual presence technologies, to extensive use of film and videos to provide a higher impact and more rapid understanding of the principles. Goal is to share conference freely and broadly.

For further information: Contact details just below.

Why Kaohsiung?

The city of Kaohsiung is taking this initiative because it realizes that most of our cities need new thinking and new approaches to resolving the insufficiencies of our present transportation arrangements, theirs included. The city is putting new ideas and real resources into their transport challenges. They have has already introduced one of the first shared bike projects in Asia, are looking into taxi-sharing, have been celebrating Car Free Days since 2003, and are building cycling infrastructure at a steady pace. Carsharing is a new idea for Kaohsiung and visitors will be able to see how they are approaching it as one more shared transport option.

The city has a spanking new metro, but the transport means of choice for about two thirds of all trips is the South Asian special, motorized two wheelers. There is something about “seeing the future” as you observe this striking pattern on the street, and it pushes the mind to consider how to come to grips wiht this new and largely unmapped phenomenon.

So when you come to Kaohsiung for the conference in September, you will also be able to take advantage of a two day new mobility tour of the city’s transportation arrangements, challenges and plans for the future. Planners and policy makers from cities around the world are going to recognize a lot of what they see in Kaohsiung.

The conference materials pack will contain extensive background on and leads to further information on each of these topic areas. To be made available before the meeting convenes.

The conference address is

For more, contact:

For Chinese media, participation, sponsor and administrative contacts:
Susan Lin, Project Leader
Mega Trans International Corporation
Hansheng East Road
Banciao City Taipei County 22066 Taiwan Tel. +886 922 661 235

For meeting logistics, overall organization and UK contacts:
Rory McMullan, Project Manager
PTRC Education and Research Services Ltd.
1 Vernon Mews, Vernon Street,
W14 0RL United Kingdom Tel. +44 (0) 20 7348 1970 Skype: roryer

For matters relating to content, ACOST, speakers, jury and moderating
Eric Britton, Program Chair:
New Mobility Partnerships
The Commons/EcoPlan international
Le Frêne, 8/10 rue Joseph Bara. 75006 Paris, France Tel. +331 4326 1323 Skype: newmobility

Home Location , Smart Growth and Sustainable Transport: Changing Patterns

A significant key to sustainable transport resides in our land use. And what more important land use decision than where we chose to live, the place in which we start or end the lion’s share of our personal travel each day? In this article our guest Todd Litman of the Victoria Transport Policy Institute sheds judicious light on claims and counter-claims of Smart Growth, as true in Delhi, Moscow or Cape Town as in North America.

Archives: Stephen Budiansky on The Physics of Gridlock

Normally the weekend is a time of rest here at W/S, but occasionally the temptation of trolling through our archives dating back to the eighties brings up something that seems every bit as relevant today as it did back then. So in this spirit, “Budiansky on The Physics of Gridlock”, Dec. 2000.

The Physics of Gridlock

What causes traffic jams? The depressing answer may be nothing at all

by Stephen Budiansky, Atlantic Monthly D e c e m b e r 2000

BERTRAND Russell once observed that animal behaviorists studying the problem-solving abilities of chimpanzees consistently seemed to detect in their experimental subjects the “national characteristics” of the scientists themselves. A divergence in the findings of the practical-minded Americans and the theoretically inclined Germans was particularly apparent.

Animals studied by Americans rush about frantically, with an incredible display of hustle and pep, and at last achieve the desired result by chance. Animals observed by Germans sit still and think, and at last evolve the solution out of their inner consciousness.

In science, Germans tend to come up with things like the uncertainty principle. Americans tend to come up with things like the atomic bomb.

The latest field to host this conflict of national styles is one that seems at first glance to offer little prospect of a sporting contest. Bigger and better highways are as American as fast-food restaurants and sport utility vehicles, and when it comes to making the crooked straight and the rough places plain, the practicality of American traffic engineers is hard to argue with. As an American academic discipline, traffic engineering is centered in civil-engineering departments, and civil engineers tend to believe in solving problems by going at them head on. A recent study funded by nine state departments of transportation to examine the doubling in congestion on urban highways and primary roads that has occurred over the past two decades listed in its final report various ways that traffic engineers have tried to alleviate the problem. These included “add road space” and “lower the number of vehicles.” This would not, as the saying goes, appear to be rocket science.

Even when American traffic engineers have ventured closer to rocket science, with computer simulations of traffic flow on multi-lane highways, the results have tended to reinforce the American reputation for practicality and level-headedness. The mathematical and computer models indicate that when traffic jams occur, they are the result of bottlenecks (merging lanes, bad curves, accidents), which constrict flow. Find a way to eliminate the bottlenecks and flow will be restored.

Such was the happy, practical, and deterministic state of affairs up until a few years ago, when several German theoretical physicists began publishing papers on traffic flow in Physical Review Letters, Journal of Physics, Nature, and other publications not normally read by civil engineers. The Germans had noticed that if one simulated the movement of cars and trucks on a highway using the well-established equations that describe how the molecules of a gas move, some distinctly eerie results emerged. Cars do not behave exactly like gas molecules, to be sure: for example, drivers try to avoid collisions by slowing down when they get too near another car, whereas gas molecules have no such aversion. But the physicists added some terms to the equations to take the differences into account, and the overall description of traffic as a flowing gas has proved to be a very good one. The moving-gas model of traffic reproduces many phenomena seen in real-world traffic. When a flowing gas encounters a bottleneck, for example, it becomes compressed as the molecules suddenly crowd together — and that compression travels back through the stream of oncoming gas as a shock wave. That is precisely analogous to the well-known slowing and queuing of cars behind a traffic bottleneck: as cars slow at the obstruction, cars behind them slow too, which causes a wave of stop-and-go movement to be transmitted “upstream” along the highway.

The eeriest thing that came out of these equations, however, was the implication that traffic congestion can arise completely spontaneously under certain circumstances. No bottlenecks or other external causes are necessary. Traffic can be flowing freely along, at a density still well below what the road can handle, and then suddenly gel into a slow-moving ooze. Under the right conditions a small, brief, and local fluctuation in the speed or spacing of cars — the sort of fluctuation that happens all the time just by chance on a busy highway — is all it takes to trigger a system-wide breakdown that persists for hours after the blip that triggered it is gone. In fact, the Germans’ analysis suggested, such spontaneous breakdowns in traffic flow probably occur quite frequently on highways.

Though a decidedly unnerving discovery, this was very much of a piece with the results of mathematical models of many physical and biological systems that exhibit the phenomena popularized under the heading “chaos theory.” In any complex interacting system with many parts, each of which affects the others, tiny fluctuations can grow in huge but unpredictable ways. Scientists refer to these as nonlinear phenomena — phenomena in which seemingly negligible changes in one variable can have disproportionately great consequences. Nonlinear properties have been discovered in the mathematical equations that describe weather, chemical reactions, and populations of biological organisms. Some combinations of variables for these equations give rise to sudden “phase shifts,” in which the solution to the equation jumps abruptly from one value to another; others set off truly chaotic situations in which for a time the solution to the equation fluctuates wildly and without any seeming pattern, and then suddenly calms down.

Such mathematical discoveries do seem to be borne out in the real world. Biological populations often exhibit erratic booms and busts that cannot be explained by any external cause. Long-term weather patterns defy prediction by the most powerful supercomputers. And a whole class of chemical reactions has been discovered in which the chemicals do not merely react and create a product, as they did in high school chemistry class, but oscillate back and forth between reactants and products. (Some especially nice ones cause color changes in the solution, so you can sit there and watch the stuff in the beaker go back and forth every few seconds.) The consistent story in all these discoveries is that the components of the system and their interactions themselves — rather than any external cause — give rise to the nonlinear behavior of the system as a whole. A rough analogy is a dozen dogs standing on a water bed. If one dog moves, he starts the bed sloshing around, which causes another dog to lose his balance and shift his weight, which sets up another wave of disturbance, until true chaos is reached.

In the case of traffic, the German physicists — principally Dirk Helbing and Boris Kerner, of Stuttgart — found that given a certain combination of vehicle density and vehicle flow rate along a highway, the solution to their equations undergoes a sudden phase shift from freely moving traffic to what they call “synchronized traffic.” Cars in all lanes abruptly slow down and start moving at the same speed as the cars in adjacent lanes, which makes passing impossible and can cause the whole system to jam up for hours.

In the traditional picture of traffic flow and congestion, the number of cars per minute that pass a given point on the highway at first steadily increases as the density of cars on the highway increases. (As long as everything keeps moving freely, the more cars there are on a mile of a highway, the more flow by per minute.) Eventually, however, further increases in density will cause a decrease in flow, as drivers begin braking to maintain a safe distance from the cars in front of them. A graph of flow versus density thus forms an inverted V shape. The uphill side corresponds to free flow, the downhill to congested flow. The Germans found, in effect, that under the right (or, rather, wrong) circumstances the solution to the equations can tunnel right through this hill without ever reaching the top, jumping from a state of (submaximal) free flow straight to congestion.

Such a leap from one state to another is like what happens when a chemical substance changes phase from vapor to liquid. It often happens that water in a cloud remains in the gas phase even after temperature and density have reached the point where it could condense into water droplets. Only when a speck of dust happens along, providing a surface on which condensation can take place (a “condensation nucleus”), does the transition finally occur. Helbing and Kerner basically found that free flow and synchronized flow can occur under the same conditions, and that under such “metastable” conditions a small fluctuation in traffic density can act as the speck of dust causing the shift from one to the other.

Worse, they found that it is easier to start a traffic jam than to stop one. The phase shifts they discovered exhibit what is known in the terminology of nonlinear phenomena as hysteresis. That is, a small and transient increase in, say, the number of cars entering a highway from a ramp can trigger a breakdown in flow, but even after the on-ramp traffic drops to its original level (in fact, even after it drops well below its original level), the traffic jam persists. Looking at actual data recorded by sensors on Dutch and German highways, the physicists found apparent examples of this phenomenon in action, in which a sluggish synchronized flow came on suddenly and persisted for hours, even after the density of traffic had dropped.

If breakdowns in flow can result from such small and random fluctuations, then the world is a very different place from the one that most traffic engineers are accustomed to. The very notion of maximum capacity for a highway is called into question, because even at traffic densities well below what a highway is designed to handle, jams can spontaneously arise. “If this flow breakdown can take place just anywhere,” says James Banks, a professor of civil and environmental engineering at San Diego State University, “then we’re in trouble, because there’s a lot more potential for congested traffic than we thought was the case. And it makes a control strategy much more difficult.”

For example, it may not be enough simply to limit the rate at which cars are allowed to enter a highway, as is now done on some congested freeways; rather, it may be necessary to time each car’s entry precisely to coincide with a transient drop in density along the main road, thus aiming to smooth out the fluctuations that can trigger a phase shift. There may even be situations in which widening roads or “metering” on-ramp flow could backfire, making flow breakdowns more likely. Preventing flow breakdowns in a nonlinear, chaotic world could ultimately require realizing an Orwellian idea that has been suggested from time to time: directly controlling the speed and spacing of individual cars along a highway with central computers and sensors that communicate with each car’s engine and brake controls.

To say that not all American traffic engineers like these discoveries in chaos theory and their implications for traffic is an understatement. Banks acknowledges that there has been a strong, almost visceral, reaction against the Germans’ conclusion, because of its assault on rational determinism and common sense, and also on what might be termed culture-of-science grounds. “Scientists and engineers are human beings,”he says, “and the first reaction is, These guys are not only physicists — they also have a knack for getting themselves in the press. So right away there’s an envy factor: Who do these guys think they are?” It doesn’t help that the German theoreticians’ papers are very difficult to understand. “They’re written in such a way that those of us who aren’t physicists never know if it’s their English, or whether they’re using physics jargon, or whether they just don’t make sense,” Banks says.

The Americans also question how well the Germans’ theoretical results relate to traffic in the real world. All mathematical models involve assumptions, and just because a model re-creates certain real-world phenomena doesn’t mean it accurately reflects reality in toto; there is always the possibility that the weird properties of the equations are artifacts of the model itself and its assumptions. The Germans’ theory “is one plausible description,” says Carroll Messer, a research engineer at Texas A&M University, using words that are obviously chosen carefully, “but that’s not saying it’s been verified.” Indeed, some American researchers have questioned whether elaborate chaos-theory interpretations are needed at all, since at least some of the traffic phenomena the Germans’ theories predict seem to be much like things that have been appearing in the traffic-engineering literature under other names for years, and these have straightforward cause-and-effect explanations. Banks published a paper in 1999 pointing out that data from monitors that record how many cars pass a fixed point — the sort of data the Germans obtained from Dutch and German highways, which they say verify their predictions — often fail to capture the complete picture of what is happening on the road. He suggests that the behavior of drivers may in fact offer a simpler explanation for the phase shifts and other nonlinear features of the Germans’ theoretical models. A sudden slowdown in traffic may have less to do with chaos theory and self-organizing phenomena of systems than with driver psychology. Synchronized flow, for example, has appeared in American traffic literature for decades, under the name “speed sympathy,” and Banks says it often happens as traffic gets heavier simply because of the way individual drivers react to changing conditions. As the passing lane gets more crowded, aggressive drivers move to other lanes to try to pass, which also tends to homogenize the speed between lanes. Another leveling force is that when a driver in a fast lane brakes a bit to maintain a safe distance, the shock wave travels back much more rapidly than it would in other lanes, because each following driver has to react more quickly. So as a road becomes congested, the faster-moving traffic is the first to slow down.

Thus many American traffic engineers insist that when breakdowns in flow occur for no apparent reason, it is only because no one has looked hard enough to find the reason, which could be anything from a bad stretch of pavement to a deer running across the road. Much work is now under way on both sides of the Atlantic on a “theory of bottlenecks” that may help to settle the matter.

Even if traffic engineers manage to slay the mathematical bogeyman that theoretical physics and chaos theory have unleashed, another bogeyman may be lurking nearby. It turns out that the properties collectively exhibited by large numbers of cars moving over a network of roadways have many mathematical features in common with the behavior of other things that flow over networks, such as data carried by telephone lines and the Internet. The mathematics of networks is a well-studied topic in communications research, and a recent paper draws on this body of theory to establish an interesting paradox about the flow of vehicular traffic: adding a new road segment to an existing network of roadways can under certain circumstances reduce the car-carrying capacity of the network as a whole. The safest advice for budding engineers may be, If you want determinacy, stick to something simple — like rockets or atomic bombs.

# # #

Stephen Budiansky is a correspondent for The Atlantic.

Copyright © 2000 by The Atlantic Monthly Company. All rights reserved. The Atlantic Monthly; December 2000; The Physics of Gridlock – 00.12; Volume 286, No. 6; page 20-24.

Op-Ed: Chaotic India has an Urban Edge

“The unprecedented urban growth taking place in developing countries reflects the hopes and aspirations of millions of new urbanites. Cities have enormous potential for improving people’s lives, but inadequate urban management, often based on inaccurate perceptions and information, can turn opportunity into disaster.”
– State of World Population 2007, UNFPA.

“I regard the growth of cities as an evil thing, unfortunate for mankind and the world, unfortunate for England and certainly unfortunate for India…It is only when the cities realize the duty of making an adequate return to the villages for the strength and sustenance which they derive from them, instead of selfishly exploiting them, that a healthy and moral relationship between the two will spring up.”
– M. K. Gandhi

Continue reading

Envisioning the Future: 21 Ways to InflateTraffic Forecasts

This is the first article in a series to which we here at World Streets give great importance: the many different ways we have of envisioning the future, hopefully a very different future. These many ways span a variety of techniques: guessing, reckoning, projecting, forecasting, scenarios, estimating, predicting, modeling, and variously describing that different future using various media: physical models, drawings, simulations, films, interactive gaming, and even imagining, wishing, hoping, storytelling, and at times even lying. The idea in all cases being somehow to “show”, to render credible, even desirable (or the opposite) that different future. However if past performance is any guide we have not always been particularly good at this. To get the ball rolling in this series let’s have a look at a new book by Robert Bain Toll Road Traffic & Revenue Forecasts which is scheduled for publication next month, and in which he looks at one part of this, for which the track record is, you will see, a bit spotty.

Big Numbers Win Prizes

21 Ways to Inflate Toll Road Traffic & Revenue Forecasts

A number of high profile investor-financed toll roads around the world are currently failing to meet expectations. Robert Bain suggests that this has less to do with the present economic climate and more to do with a market readiness to be seduced by hopelessly optimistic traffic and revenue projections; lenders relying too heavily on elaborate transaction structuring for protection. The time is right for a paradigm shift, he maintains, with a renewed emphasis placed on understanding the demand fundamentals and less willingness to accept forecasts at face value – especially those that resemble statements of advocacy rather than unbiased predictions.

The evaluation criteria used to award many of today’s toll road concessions focus on maximising income – or minimising expenditure – for promoters. These criteria establish the rules of the game. Bidders are incentivised to develop strategies which best respond to the criteria – framing their bids in a positive light and maximising their chance of winning the competition. Under such circumstances, traffic and revenue forecasts are bound to attract considerable attention.

Bidding strategy success and the ability to raise significant quantities of debt often rely on strong projections of demand; even beyond credibility in situations where the short-term benefits of winning overshadow any possible longer-term costs. This is true in cases where profits are front-loaded or where, for practical or reputational reasons, procuring agencies may be open to subsequent contractual renegotiation. In short, the procurement process in general – and bid evaluation criteria specifically – reward high traffic and revenue forecasts, not accurate ones. This places asymmetric pressure on traffic advisers in terms of the outputs from their forecasting models. In this context, the following article summarises 21 ways in which toll road traffic and revenue projections can be inflated – tricks for investors to watch out for.

1. Flatter the Asset

The representation of a toll road in a traffic model may be flattered in various ways. An incomplete treatment of the delays that drivers experience at toll collection stations or upon leaving the toll road (and re-joining a congested toll-free network) makes the toll road more attractive to potential users. So does exaggerating the capacity per lane. Traffic modellers commonly employ assumptions about how the capacity of a toll facility will increase in future years despite its geometry and configuration remaining unchanged! This is supposed to reflect that fact that driver behaviour adapts over time such that the ‘effective’ capacity of a road will increase. Naturally, this improves the attractiveness of the asset. Evidence should be provided by traffic advisers to support such assumptions if they are to be incorporated in base case traffic models.

An alternative approach is to impair the competitive landscape. The competitive position of a toll road will appear to be strong in circumstances where the alternative facilities offer particularly poor levels of service to users. This can be achieved by degrading a competing route’s capacity through the use of punitive speed/flow relationships or speed limits, or by over-emphasising delays (such as those experienced at signalised intersections). It can also be achieved by over-simplifying the competitive context – ignoring important rat-runs in an urban network or by neglecting the potential for competition from other roads or transportation modes in the future.

2. Cherry-Pick your Planning Variables

The future-year socio-demographic and planning variables that are used by traffic models are commonly presented as ranges. Consistent selection of values from the upper ends of these ranges will place upward pressure on the traffic numbers. This is one of the reasons why all of a model’s input assumptions should be tabulated on a single sheet and justified – with supporting evidence being provided by the traffic adviser.

A variation on this theme is the use of planning variables designed to achieve particular political objectives. A recent report reviewed talked of “planning targets”. These seemingly independent and unbiased variables – such as projections of population – may be the basis upon which the state allocates funds to regional government. There are incentives for the producers of these planning forecasts to inflate their own projections which, in turn, can be used to pump-up the traffic numbers. Understanding the source(s) of these ‘independent’ socio-demographic and planning variables can help to mitigate this risk. Presenting alternative planning forecasts from different public and private sector sources also provides some comfort to investors.

3. Judiciously ‘Identify’ the Historical Trend

With a time series of data – such as traffic or toll revenue – it is often possible to isolate different trends by carefully selecting the period to be analysed. Figure 1 shows the time series of revenue miles from the Pennsylvania Turnpike. From opening year (1941) to 2006 the compound annual growth rate was 5%. From 1952 to 2006 the rate was only 3%. However, in terms of supporting high traffic forecasts, from 1943 to 2006 the rate was a very useful 7%. These different growth rates are all derived from the same historical data set – just different parts of it.

4. Selectively Apply or Report Growth Factors

Traffic and revenue study reports commonly provide area-wide statistics in support of their forecasts. A report might state that, across the study area from 2010 to 2030, average population growth of 1.2% per annum is predicted. This appears reasonable – possibly even conservative. But what about the distribution of this growth? If the model is specified such that most of the population growth takes place in zones adjacent to or that feed the toll road, it would be no surprise to find high traffic growth rates resulting on the asset itself – usually considerably higher than 1.2% per annum!

5. The Future Will Look Exactly Like the Past

Some toll road forecasts are made against a backdrop of strong historical traffic growth trends. Why should such trends continue unabated for the next 25-30 years or beyond? And what about historical relationships – such as the elasticity between GDP growth and traffic growth? Why should this relationship remain constant throughout the forecasting horizon? These are for the traffic forecaster to justify – particularly if senior debt accretes or debt amortisation schedules are back-ended. In the absence of solid justification, base case forecasts should be adjusted accordingly to reflect the increasing uncertainty associated with long-range projections and sensitivity tests should be used to evaluate the impact of key relationships which could change in the future.

6. The Future Will Look Nothing Like the Past

A recent traffic and revenue study reviewed by the author demonstrated clearly that historical traffic growth across the study area had neither been strong nor consistent. Along some key corridors traffic volumes had been declining. Yet the future, according to the traffic forecasts, was one of strong, sustained growth. No explanation was provided for this dramatic disconnect between the past and the future. At best this hints of model-blindness. The traffic adviser has been engrossed in the mechanics of model building to the extent that they become blind to the credibility of the model outputs. Other symptoms of possible model blindness recently noted include low growth scenarios that resulted in traffic and revenue projections above the base case and severe downside sensitivity tests that had little impact on project revenues. Just because the model reports certain results does not mean that they have to be assumed to be credible.

7. Using Seasonality to Your Advantage.

Traffic surveys should be conducted on neutral days and during neutral months of the year. These are ones which are typical in terms of trip-making patterns and traffic conditions. This is not always possible, but failure to take proper account of factors such as seasonal variations can lead to erroneous modelling results.

Figure 2 shows the impact of seasonality on roads in Cornwall – a popular tourist destination in the south west of England – and compares traffic patterns there with the UK average.

Whereas the national trend demonstrates some seasonality, it is mild in comparison with that recorded in Cornwall. Traffic in Cornwall in August is 35% higher than the annual average. Figure 2 shows just how atypical certain months of the year can be. Days of the week can demonstrate similar variability. Compare market-day traffic with that from an average weekday. Without appropriate adjustment, surveys conducted on atypically busy days or during atypically busy months will overstate the amount of trip-making in an area and will lead to higher projections of traffic.

8. Remove Inconvenient Truths

This is best illustrated by example. Take a journey time survey involving five separate runs along a toll-free alternative to a proposed toll road. The run times are shown in Table 1.

The run time average is 12 minutes (top line). However, Run 4 was quicker than the others by some margin. If this is treated as an outlier – and is discarded – the average run time becomes 13.5 minutes (bottom line). This is useful as it degrades the attractiveness of the alternative facility and boosts the competitive standing of the toll road.

The difference between 12 and 13.5 minutes may appear insignificant, however some demand estimation techniques are very sensitive to small changes in the characteristics of competing alternatives. These small changes can have a disproportionate impact on the percentage of traffic projected to use the toll road. Traffic advisers should report how stable their estimates of market capture are to small changes in the competitive landscape – but seldom do.

9. Design Surveys to Return the Required Results

Transport researchers acknowledge that it is possible to achieve specific results from some survey types through judicious design and administration. Similarly, it is possible to bias the results through poor design and administration. This is particularly true in the case of Stated Preference surveys where respondents’ choices between alternative travel options are influenced by factors such as how those options are portrayed, the range of attribute levels presented and the absence of any opt-out choice (forcing an outcome on respondents).

This is not to suggest that Stated Preference techniques are inherently flawed. Good practitioners are alert to these issues and should be able to minimise such influences. However investors should look for some comfort in this regard – ensuring the use of experienced firms in this field – alert to the fact that it remains possible to affect survey output through the judicious contexting, selection and definition of the questions being asked to interviewees.

10. The Magic of Expansion/Annualisation Factors

Traffic models focus on critical times such as weekday AM peak periods – in part, for convenience. Expansion factors are then used to gross-up the results to annual estimates (toll revenue per year, for example). The smaller the modelled time period, the more emphasis is placed on expansion factors – and small changes to the factors can have a significant impact on the final revenue calculations.

Say that a traffic model suggests that, during a weekday AM peak hour, 1,600 vehicles use a toll road paying an average of $1.50. Two alternative sets of expansion factors are presented in Table 2 (Scenario A and B).

The expansion factors under Scenario A result in an annual revenue estimate of $4.8m. Using the alternative – yet still plausible – factors under Scenario B, the revenue is $6.6m (40% higher). This significant difference has nothing to do with the traffic model. It results from the use of different expansion factors. Traffic advisers should explain their choice of values used and should conduct and report the results from sensitivity tests if revenue projections appear to be particularly factor-dependent. Unlike the simple example presented here, the expansion process behind some forecasts can be complex. It is important that investors understand this process particularly well.

11. Assume that Consumers Act Rationally

It is easy to underestimate the reluctance of some (sometimes many) drivers to paying tolls. Even in circumstances where the time savings appear attractive, it is possible to observe drivers sitting in heavily congested traffic conditions just to avoid paying a relatively modest charge. This may appear to defy logic – and be contrary to what a traffic models suggests – but it can be observed nevertheless. For this reason, investors should pay particular attention to any revealed preference data (from comparable facilities) presented in support of toll road projections – or the absence thereof.

12. Assume that Consumers Make the Same Choice Every Time

An urban toll bridge in San Juan, Puerto Rico illustrates this issue well. It caters mainly for commuter traffic heading for the capital’s downtown business district. The tariff is $1.50 (cars) and the traffic model over-estimated demand by 46% in the first year of operations. Subsequent analysis of travel patterns on the bridge revealed that commuters were not using the bridge in each direction, nor were they using it every day. Commuters were using the bridge selectively. They were more inclined to pay to hurry home than they were to pay to hurry to work – and this effect became more pronounced towards the end of the week.

The cost proposition in the traffic model was a one-off payment of $1.50 (for x minutes of time saving). However if commuters used the bridge twice a day, five days a week, the cost proposition was $15/week. Although not captured by the model, this was the cost that drivers faced and responded to. Hence their selective use of the asset. Models which fail to capture such behaviour will produce inflated projections of traffic and revenue.

13. Hypothetical Bias: A Helping Hand?

Stated Preference (SP) surveys are widely used in transport studies because they are one of the few techniques that can measure the market and non-market values associated with consumer products such as toll roads. The technique remains somewhat controversial. Investors cannot be certain of the accuracy of the SP value estimates since SP surveys are hypothetical in both the payment for and the provision of the service in question. Most research suggests that people overestimate the amount they would pay for a service when they do not have to back-up that choice with a real commitment (hard cash). This is called hypothetical bias and is well documented in both laboratory and field settings. Researchers suggest that mean hypothetical values could be 2.5 to 3 times greater than actual cash payments would be.

There are some limited contradictory findings which suggests that SP underestimates the amount that people would be willing to pay in real life. Notwithstanding, investors should be aware that there are professional concerns about SP and hypothetical bias – particularly when interviewees remain uncertain about their responses. The majority view is that, when present, hypothetical bias is likely to overstate (inflate) the consumer response. This is another reason why revealed preference data – hard evidence – should be provided alongside SP survey results whenever possible.

14. Grow Your Value of Travel Time Savings

The value of travel time savings (VTTS) is a central concept in toll road demand studies. It is a large topic in itself. Here we concentrate on just three aspects. The first is the concept of growth in the VTTS as it is common for traffic consultants to use growth assumptions about the VTTS in toll road forecasting models. The underlying theory suggests that disposable income will grow – in real terms – in the future and hence the value attributed to time savings should also grow in the future. Forecasts of GDP are often used as a proxy for the growth in disposable income, although the growth factor applied to VTTS may be higher (eg. 1.2x disposable income growth).

Increasing the value of time savings boosts toll road usage in future years. There may be arguments in support of such an approach – and these should be articulated – however the impact of this growth is commonly material, and should be isolated and understood by funders who may feel that, in some situations, it has the scent of equity upside.

There is a second issue regarding time savings that is pertinent to mention here. It concerns small time savings. The conventional approach is to say that the driver who values a time saving of one hour at $20 automatically values a saving of three minutes at $1. This is known as the constant value approach and it has attracted a vocal body of critical opinion. Researchers suggest that small amounts of saved time are inherently less useful than large amounts – particularly if you cannot do anything with the time saved – and that small time savings may go unnoticed (hence unvalued) by travellers. Assumptions about small time savings have a particular relevance in the context of short tolled sections of road, bridges or tunnels. The recent revenue underperformance of some urban toll tunnels in Australia, for example, may, in part, be attributed to overestimating the price consumers are willing to pay to save relatively small amounts of travel time.

There is also the issue of VTTS in congested traffic conditions. Some traffic advisers maintain that the VTTS varies according to congestion levels and values over 1.5x the base value have been noted. Traffic advisers draw parallels with the value of waiting time in public transport models (which is typically higher than the value of travel time – reflecting the perception of time passing slowly while waiting). The impact is for more trips in the model to assign via the tolled facility and the effect – helpfully – compounds in the future as congestion intensifies across the network.

15. Overstating the Toll Road Premium

Some traffic models incorporate the use of a toll road premium or bonus to capture the inherent attractiveness of toll roads. This suggests that if a toll road and its toll-free competitor are matched, taking account of the toll paid and the time saved, instead of traffic assigning on a 50:50 basis, proportionately more traffic will use the toll road. The premium is supposed to encapsulate those characteristics of the road not fully estimated in the model (softer attributes that are more difficult to quantify like ride quality or perceived safety). The impact of this premium is replicated in models that, alternatively, penalise links that compete with the toll road.

The danger here lies in overestimating the premium – overstating the inherent attractiveness of the asset. This inflates revenues. Any toll road premium employed by traffic consultants should be made explicit and should be justified – to the extent of re-running the model in its absence to determine the contribution to revenues made by assumptions about the premium alone.

16. Overstating the Yield

Yield refers to average revenue/vehicle. As most toll roads are dominated by private car use, the yield generally lies close to the car tariff. Because of the proportionately higher tariffs, the greater the contribution of trucks and buses to the traffic mix, the higher will be the yield. Overestimating the number of trucks using a toll road will disproportionately inflate aggregate revenues. This is a particular concern as truck usage of toll roads is notoriously challenging to predict and has often been overestimated.

Yield calculations can also be overstated if unrealistic assumptions are made about the take-up of discount programmes. Similarly, unrealistic estimates of toll avoidance and/or exemptions will overstate yield. Investors need to understand not only what revenues are forecasted, but the composition of these revenues and any (and all) assumptions underpinning them.

17. Reliance on Speculative Development

Future land use plans are a key traffic modelling input – however there may be questions about how committed some development proposals actually are. The reliance that can be placed on land use plans is a challenging issue in economies experiencing rapid growth – especially under less-regulated planning regimes – however it is also an issue in many developed countries.

Purely speculative developments should be omitted from base case traffic forecasts. Similarly, developments expected to result from the building of new tolled facilities should be treated cautiously in terms of their contribution to traffic. Speculative and generated developments in toll road demand models simply serve to inflate the traffic and revenue projections.

18. The Joy of Induced Demand

Building new highway infrastructure generates traffic however the relationship is far from clear or consistent. Often toll road traffic forecasters make an assumption about generated (induced) traffic and add this to their forecasts. An upwards adjustment of 10% is not uncommon – however it is seldom supported with evidence.

Investors should identify if such an adjustment has been made to the traffic figures they are reviewing and then consider the evidence. In some circumstances the contribution from induced traffic has been removed from base case forecasts reflecting the fact that considerable uncertainty surrounds this revenue contribution. As before, induced traffic helpfully serves to inflate project revenues.

19. Introduce Your Own Toll Discount

There is some evidence to suggest that, in terms of toll road usage, drivers respond differently to different toll road payment media – particularly non-cash options. By using electronic toll collection (ETC) technologies, drivers do not have to pay the toll at the time/point of use. The charge is made to their credit card account and they are billed, in arrears, on a monthly basis. It is suggested that this encourages toll road usage above and beyond what would be expected from a cash-only operation. To capture this effect, traffic modellers talk about a ‘perceived ETC discount’ – the discount reflecting users’ misperceptions of the price paid due to electronic tolling and the payment deferral. This is entirely separate from (and in addition to) any real discount enjoyed by ETC scheme patrons.

In a recent study, the perceived ETC discount was set at 15% and tariffs were accordingly reduced to 0.85x their face value. Reducing the price encourages toll road use and inflates the traffic figures. Investors should look for evidence in support of perceived ETC discounts in traffic studies if they are to accept the use of artificially reduced tolls in base case projections.

20. Assume Quick Ramp-Up

Ramp-up is the period upon the opening of a tolled facility when drivers experiment with new routes. It is a period often characterised by strong growth (from a low base) and it ends when trip-making patterns stabilise and evolve into more mature trends. It is notoriously difficult to predict in terms of its depth and duration. Traffic consultants often assume a ramp-up profile based on instinct or weak evidence with questionable transferability.

The use of instant or short ramp-up assumptions runs the danger of inflating early-year revenue forecasts. Ramp-up assumptions should be challenged to understand their underpinning rationale. It may be sensible to run sensitivity tests using alternative assumptions to ensure that the financing remains robust during the early years of project operations and throughout the remaining term of the concession.

21. Ignore Physical (or Operational) Capacity Constraints

It may seem incredible that some forecasts have actually exceeded the physical capacity of their road (in terms of volume/lane/hour) but it has been noted – particularly when these forecasts result, not directly from traffic models, but from traffic model figures extrapolated into the future. Typically no mention is made of widening or the costs (and disruption) involved in capacity expansion. Turning from volume/hour to volume/day, another phenomenon observed has been the fact that some forecasts of daily traffic (AADT) would required roads to operate at peak-hour congestion levels for over 12 (sometimes over 18) hours/day. These highly uncharacteristic flow profiles should certainly raise investor questions.

The recent development of managed lanes with dynamic pricing – particularly in the US – introduces concerns about how forecasts may exceed a highway’s operational capacity. On some managed lanes, the tariff is adjusted based on the volume of traffic using the facility. As usage goes up, the toll goes up – with a view to constraining demand such that a certain level of service can be offered to drivers. Traffic forecasts recently reviewed from one project, however, were so high that they would have degraded the level of service to below that required contractually of the concessionaire. High-Occupancy Vehicle (HOV) and HOV/toll (HOT) lanes – and other initiatives that fall under the ‘managed lane’ concept – are relatively new and present particular methodological challenges to traffic modellers. They are commonly crudely or incompletely represented within the model – although this fact is seldom highlighted. Investors reviewing these more innovative tolling applications need to ensure that, in terms of modelling, traffic advisers explain clearly what has been achieved, how and – importantly – the limits of these achievements.


The list of 21 ways in which toll road traffic and revenue forecasts can be inflated is not exhaustive. It is purely indicative. There are others – some of which are highly technical and would require forensic work to uncover (such as the careful positioning of centroid connectors). Other techniques are more general and rely upon clouding detail – such as obscuring daily traffic volumes (which people understand) by reporting vehicle kilometres/year (which no one can). Or obscuring the relationship between traffic and revenue by simply reporting project revenues. This way, the recipient of the forecast has no idea how much traffic is supposed to be paying how much toll. The results cannot be sense-checked or compared with the findings from other studies.

Good traffic consultants know how to fine-tune their models. That is what model calibration is all about. In an environment where prizes are commonly awarded to the bidding team with the highest numbers, fine-tuning may be open to abuse. The purpose of the list is not to alarm investors. It simply demonstrates that it is perfectly possible to inflate the numbers for clients who want inflated numbers, and highlights some key issues to watch out for.

To knowingly inflate traffic and revenue projections is an act of deception – but it is not alone in that regard. Investors reviewing toll road studies should remain alert to two other potential acts of deceit. The first concerns sensitivity tests. Suspicions should arise when sensitivity tests have limited adverse impact on project traffic or revenues. Under certain circumstances this is possible, but it is not the norm. Good explanations should be provided in support of such results.

The second act of deceit concerns the use of pseudo-science to infer a precision of foresight that is simply not supported by empirical evidence. Favoured ploys include the presentation of narrow confidence intervals around base case forecasts and the abuse of exceedance probabilities. Traffic advisers sometimes talk in terms of P95 values – inferring that there is only a 5% probability of that particular number (traffic volume or revenue) not being achieved. However these exceedance probabilities are unlike those associated with scientifically-measurable natural phenomena such as the measurement of wind to determine energy yield predictions for wind farm financings. At best, they result from consultants attempting to re-cast their traffic model in a simple probabilistic framework. At worst, they are simply guesstimates.

Proper analysis of any traffic or toll revenue projections presented as probabilities requires a sound understanding of the probabilistic model construction, the probabilistic variables and their distributions and the correlations among the probabilistic variables. No comfort should ever be taken from P95 figures alone. If there really was as little uncertainty in the forecasts as some sensitivity tests, confidence intervals and P95s have suggested, traffic advisers could remove the legal disclaimers from their reports and could cancel their professional indemnity insurance. These trends have not been observed to date.

Robert Bain runs his own consultancy providing technical support services to investors, insurers and infrastructure funds. This article is an abridged extract from his forthcoming book ‘Toll Road Traffic & Revenue Forecasts: An Interpreter’s Guide’. Further details are available from Rob at

Correspondents/Eyes on the Streets update:

We are about to enter into the second month of World Streets existence, and are almost a week into the construction of our new World Streets Sentinels Map, so let me take a few minutes of your time to try to update you quickly on where this is heading from this point on.

1. Moving target: if you are a little confused about how all of this is supposed to work here at the beginning, let me assure you that you are not the only one. What we are setting off on here is a collaborative communication learning process, the basic underlying philosophy and broad goals of which are I hope pretty clear (see today’s opening editorial), with the rest to evolve as we move ahead and learn. I am comfortable with that and hope that you will be as well.

2. Peer-to-peer: I have always considered that one of the goals of a really successful public interest contribution is that it is wide open – i.e., that it provides materials, clues and tools which can help enable good things to happen without necessarily the provider of the tools of the initial ideas for ever emerging as the necessary central fulcrum of everything that the initial push might set off. This is definitely one of the objectives of World Streets, and I hope that you will take this as an invitation to run with any of this with your own ideas and initiatives. Of course I have to hope that whatever it is will be consistent with the basic philosophy we so strongly believe in, but in any event I am confident that the quality of the fundamental ideas and philosophic principles is sufficient to guarantee that this will pretty much have.

3. Correspondent contributions: As originally promised this is a no obligation activity, and I propose that in the first months the pattern that will suit you best will be the one that we mutually learn as the project advances. Again the sections Contributor Guidelines and Correspondents are useful as background reading which I can heartily recommend prior to posting or commenting if you will. I might add that we have particular interest in contributions which will fall under the categories including Honk!, the infamous Bad News Department, Toolkit , outstanding new projects or programs, people or groups that are making a difference, and basically anything that might be going on in your city or area of interest which has universal interest and potential application.

4. Eyes on the Street map. This is a pretty good microcosm for the rest. It is intended to illustrate in a striking manner the way in which we are attempting to combine the global and the local. There are a couple of ideas that we are looking at integrating into both this map and the project overall:

Local identification: Each city symbol needs to link to a specific person and a specific place. When you click a city, take Pune in India as example, this will take you direct to Sujit. I have tried to take him at his exact address in his neighborhood, 383 Narayan Peth, but I am going to need a little help from him in order to pinpoint the exact location of his home. I hope that we will be able to do this for all of our cooperating colleagues. (You will hopefully appreciate in this context why I have so doggedly insisted on the initial identification encompassing both the name of our cooperating colleagues and the city/country affiliation. Also In this regard, kindly you make sure I have your exact street address so, as close as possible to attaching it to your listing.)

Green Map: I am also playing around with the concept of linking each city to a Green Map (See As part of this, have already placed links not only in going but also in Barcelona, Seattle, Cape Town and one or two others.

Traffic cams: Another possibility that I intend to have a closer look at is that of finding the nearest traffic cam so that the visitor can get some kind of feel for what the streets actually look like at different points in time in that place.

4. Expanding World Streets coverage: We already after less than a week have more than 40 kind colleagues who have indicated that they will be pleased to exercise this item street function in their city and more broadly. I would hope during the course of April, the second month our new journal, to bring this up to ensure coverage of something like 100 world cities, i.e. cooperating colleagues.

Geographic: More coverage of Africa, the Middle East, the former parts of the Soviet Union and the Eastern Bloc, Latin America and Asia are definitely called for as priorities. And I think we should be very ambitious about coverage in both China and India.

Gender: One of the basic pillars of this project is that we need to engage more women in the process of planning and decision-making. Thus far of the first 40 correspondence coming in, only eight are women. To rectify this, I intend to adjust the outreach in these next ages to give heavy reference to qualified female colleagues, so if you have nominations for me please be sure that they will be immediately activated.

Sorry to have tied up so much of your time with this, but I think it is important that we get off to a strong start and a shared understanding of the best way to go about all this. Of course as always your suggestions, corrections, and ideas for doing better are enormously well.

Eric Britton
Editor, World Streets