Does building more roads create more traffic?

Tunnel vision: the claim that more roads equals less congestion fails to acknowledge the wider picture. Image: Martin Fisch via Flickr.

Congestion is a major source of frustration for road users and has worsened over time in most cities. Different solutions have been proposed, such as introducing congestion charging (a favourite of transport economists) or investing in public transport. The solution put forward most often is to build more roads. But does this approach actually work?

A recent study in the United States identified Los Angeles, Honolulu and San Francisco as the top three most gridlocked cities in the United States. All of these cities use almost exclusively road-based solutions to transport citizens. Meanwhile, China has increased its expressway network from 16,300 km in the year 2000 to around 70,000 km in 2010. Yet the average commute time in Beijing increased by 25 minutes between 2012 and 2013 to 1 hour and 55 minutes.

So why do residents of these cities not live in a driving utopia, despite their huge amounts of road capacity? 

Induced demand

The first thing to get your head around is a concept called induced demand.

Think about the street where you live. If a new road makes driving to work quicker, you may benefit from that.

But this reduced travel time might be enough to encourage two other people in your street to start driving; and two more people in the next street; and two more people in the street after that; and so on. Very quickly, the drive to work takes just as long as it ever did.

In transportation, this well-established response is known in various contexts as the Downs-Thomson Paradox, The Pigou-Knight-Downs Paradox or the Lewis-Mogridge Position: a new road may provide motorists with some level of respite from congestion in the short term, but almost all of the benefit from the road will be lost due to increased demand in the longer term.

To add insult to injury, while more roads may solve congestion locally, more traffic on the road network may result in more congestion elsewhere. In Sydney, for example, the WestConnex may improve traffic conditions on Parramatta Road, but may worsen congestion in the city as a whole.

Weakest links

Congestion is determined by the weakest links in the road network. If road capacity expansion does not involve widening of these bottleneck links, congestion may simply move to another part of the network without solving the congestion problem. Moreover, it could potentially make congestion across the network even worse.

The Braess Paradox is a famous example in which building new roads in the wrong location can lead to longer travel times for everyone, even without induced demand, because new roads may lead more car drivers to the weakest links in the network. The reverse may also be true: removing roads may even improve traffic conditions.

This paradox occurs because each driver chooses the route that is quickest without considering the implications his or her choice has on other drivers. Car drivers only care about the number of vehicles in the queue in front of them and do not care about vehicles queueing behind them. This is a classic problem in game theory, very similar to the type for which John Nash was awarded a Nobel Prize.

Building, widening or duplicating toll roads and freeways may just induce more people to choose cars over public transport. Image: KRoock74 at Wikimedia Commons.

What does the data say?

One US study has shown a strong relationship between the amount of new road length and the total number of kilometres travelled in US cities, a finding the authors of that study termed “the fundamental law of road congestion”.

Similar findings are reported in Spain and in the United States, where even major road capacity increases can actually lead to little or no reduction in network traffic densities. It has also been found to exist in Europe, where neglecting induced demand has led to biases in appraising of environmental impacts as well as the economic viability of proposed road projects.

New South Wales Premier Mike Baird’s successful re-election campaign promised motorists more roads and less traffic.

In Sydney, there is similar evidence from traffic volumes crossing the harbour. The Sydney Harbour Bridge was carrying a stable traffic volume of around 180,000 vehicles per day from 1986 to 1991. The Sydney Harbour Tunnel opened in 1992, and the total volume of traffic crossing the harbour increased in 1995 to almost 250,000 vehicles per day. This 38 per cent increase in traffic can be attributed to induced demand and not to population growth (which was around 4 per cent during this period).

Empirical observations have also confirmed the existence of the Braess Paradox. For example, in 1969 a new road was built in Stuttgart, Germany, which did not improve the traffic conditions. After closing the road again, congestion decreased.

Similar observations in which road closure led to improved traffic conditions have been observed in New York City, where upon closing 42nd street (a major crosstown street in Manhattan) it was observed that traffic was significantly less congested than average.

A recent experimental study confirmed that this paradox still exists by showing that expanding road capacity can result in worse traffic conditions for everybody.

The theory of induced demand is accepted by a large majority, but not by everyone – the authors of a 2001 paper argued that induced demand does not exist. However, UK researchers Goodwin and Noland have criticised this study.

In isolation, building more roads can certainly improve traffic conditions, but these effects may only be local and short run. Roads alone do not solve congestion in the long term; they are only one (problematic) tool in a transport management toolkit.

Matthew Beck is a Senior Lecturer in Infrastructure Management, and Michiel Bliemer Professor in Transport and Logistics Network Modelling. Both work at the University of Sydney. 

This article was originally published on The Conversation. Read the original article.


“This is a civic pride for the digital age”: why we should why we should willingly let City Hall have our data

He was the future once: David Cameron discusses smart cities with Angela Merkel and a German technology executive. Image: Getty.

Victorian England. From the shadows of wealth grew poverty. Slums slumped against symbols of civic pride, cowering next to towering town halls funded through rich merchant princes, whose elitist rule was insufficient to deal with too many people in too few houses with too little infrastructure.

Enter municipality. With darkness came electric light; with disease came tunnels to disperse their cause; with time came reform, regulation and the rise of town planning.

It’s over a century since those places which first industrialised became those first urbanised; yet even the wealthiest cities in the world continue to struggle with the complexities of urbanisation. In London, ten thousand die each year from pollution; in New York, six times this amount reside in homeless shelters.On the rush-hour roads of Sydney, cars stand still, and in the ‘burbs or banlieues of Paris slums still stand.

An umbrella bought during a downpour costs more than one bough under blue sky – and the truth is that, for too, long city halls have failed to forecast and so incurred greater costs. It’s a reactive culture summed up by words first head in Jimmy Carter’s budget office: if it ain’t broke, don’t fix it. Disease before sewer, gridlock before investment, collapse before rebuild – visible fix over unseen prevention

But with the world’s urban population growing by 65m every year, this has to change: there is not enough resource to manage cities reactively. Enter technology and the move to smart cities.

From Barcelona to New YorkOxford to Amsterdam, Singapore to Seoul: billions of low-cost devices are being installed into everyday objects to send and receive data: street lights recording pollution, and bridges reporting performance; traffic lights that count, and whose analysis will be counted upon, to ease traffic congestion; health wristbands understanding our heart’s needs, shop ceilings noting our heart’s desires. A web of information woven into the very fabric of cities which, when added to data from sources like mobile phones, is providing a living-breathing picture of how we and our cities operate.

This data is no longer retrospective or historic but live and dynamic. It is of such quantity, and can be analysed at such granular detail, that it can provide certainty where once there was only supposition. It is build-up before the gridlock, illness before epidemic; the crack of an ageing bridge, the first signs of smog. It is diagnostic to preventative. Umbrella under blue sky.

Those promoting the “internet of things”, estimated to be worth $11.1trn a year by 2025, will declare it a panacea – but it is not, at least not entirely. Sure, challenges regarding data quality, privacy, standardisation, and security will be overcome; 4G will become 5G will become 6G. Devices will communicate intelligently with each other – autonomous vehicle to autonomous vehicle, autonomous vehicle to bridge, drone to home. Data will become as fundamental to cities as infrastructure, and will be referred to as such.

Yet city halls in democracies, whilst infinitely better informed, will continue to make their decisions which are restricted by commercialism, framed by political ideology, and driven by short-term electoral or media pressures.

People first

From the mid-sixties to the start of this century a UK television programme called Tomorrow’s World showcased future living. For every correct prediction (mobile phones) came countless incorrect ones: the floating-bicycle, say, or paper underwear. My point is that only a small part of understanding the future of cities is about understanding technology. The majority is about understanding people and society, the people from whom the very word “city” is derived: civitas, the collective of citizens.

Gutenberg did not change the world by inventing the printing press in the 13th century – but he did enable the world to change. The technology was the printing press, the outputs were books filled with knowledge, the outcomes were the actions of the many who used that knowledge. Technology is a tool, a process towards an outcome. 

In much the same way, the Internet of Things will not change the world – but it will enable the world to change. Sensors are the technology, data the outputs, the analysis of this data and subsequent decisions, the outcome.

It is crucial to avoid the Tomorrow’s World approach. That is, racing to implement technology first without consideration of identified social, economic or environmental needs; introducing more complexity when most citizens seek simplicity. As the writer and urbanist Jane Jacobs once said:“First comes the image of what we want, then the machinery is adapted to turn out that image.”

Start with people. Form the image. Think of technology through the Greek origins of the word, techne and logos – a discourse about the way things are gained – and capitalise on collective intelligence to move towards that image.

Since cities first started to appear some millennia ago, they’ve provided incontrovertible evidence that the wisdom of crowds is far greater than the individual; that collective intelligence gained from that trinity of city institutions – citizen, government, industry – surpasses what can be achieved by any one in isolation. Where would Apple, Uber, or Google be without the government-backed inventions like the world-wide-web, touchscreen technology, WiFi or global positioning systems?

A new civic pride

Of course, an app on a smart phone that can ask a thousand questions is meaningless if nobody feels motivated to answer. Increasing urbanisation brings increasing interdependency: lives intrinsically linked, services shared. The challenge for city halls is to turn the increase in what people have in common, into an increase in common purpose, through understanding the three benefits that motivate and lead to action.

Extrinsic benefits, of status and reward, caused merchant princes to fund city halls in Victorian England: such benefits today see the ambitious putting in extra hours. Intrinsic benefits, like competitiveness or fun, that once caused business tycoons to compete to build the tallest skyscrapers, now explain why “hackathons” and “city challenges” are such a success. Then there are the pro-social benefits of altruism or benevolence, that cause millions to volunteer their time to give back and feel part of something bigger than themselves.

These motivations are of greater significance, because there are no longer people with clipboards standing on street corners asking permission to collate our views on services: it is happening automatically through the Internet of Things. Our choices online, movements offline; the travel we take, the pollution we make; our actions and interactions. We are data.

City halls can take a click-box-small-print approach to this, like so many apps. But there is opportunity to do the opposite. They can promote the fact that citizens can knowingly provide their data towards making lives better; visualise and enable citizens to see and understand their input, alongside data provided by others.

They can incentivise interaction with data, so that entrepreneurs can work back from outcomes, solve challenges, and re-localise where appropriate (we should not need a multinational to get a taxi). They can be proudly open, enabling citizens, industry and government to receive pro-social benefit by contributing to something bigger than themselves: their life and the lives of others.

This is a civic pride for the digital age. Not just localism or patriotism based on geography but the strength of connection between people and their ability to direct and determine change through data. Not just pride in the buildings and infrastructure that form our physical world, but in the quality of data that will shape our future world and move us from a diagnostic to preventative society – umbrellas under blue sky.

We should take pride in technology, yes; but that should come second to the pride in those who, enabled by that technology, drive progress. Who, through the wisdom of crowds, form an image of the future and strengthen democracy by motivating society to move towards it. Who embrace openness and help overcome the challenges of urbanisation.

Kevin Keith is a writer, researcher, urbanist, and director of the southern hemisphere’s largest open data competition, GovHack. He tweets as@KevKeith.

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