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.

 
 
 
 

A nation that doesn’t officially exist: on Somaliland’s campaign to build a national library in Hargeisa

The Somaliland National Library, Hargeisa. Image: Ahmed Elmi.

For seven years now, there’s been a fundraising campaign underway to build a new national library in a nation that doesn’t officially exist. 

Since 2010, the Somali diaspora have been sending money, to pay for construction of the new building in the capital, Hargeisa. In a video promoting the project, the British journalist Rageeh Omar, who was born in Mogadishu to a Hargeisa family, said it would be... 

“...one of the most important institutions and reference points for all Somalilanders. I hope it sets a benchmark in terms of when a country decides to do something for itself, for the greater good, for learning and for progress – that anything can be achieved.”

Now the first storey of the Somaliland National Library is largely complete. The next step is to fill it with books. The diaspora has been sending those, too.

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Some background is necessary here to explain the “country that doesn’t exist” part. During the Scramble for Africa of the 1880s, at the height of European imperialism, several different empires established protectorates in the Somali territories on the Horn of Africa. In 1883, the French took the port of Djibouti; the following year, the British grabbed the north coast, which looks out onto the Gulf of Aden. Five years after that, the Italians took the east coast, which faces the Indian Ocean.

And, excepting some uproar during World War II, so things remained for the next 70 years or so.

The Somali territories in 1890. Image: Ingoman/Wikimedia Commons.

When the winds of change arrived in 1960, the British and Italian portions agreed to unite as the Somali Republic: a hair-pin shaped territory, hugging the coast and surrounding Ethiopia on two sides. But British Somaliland gained its independence first: for just five days, at the end of June 1960, it was effectively an independent country. This will become important later.

(In case you are wondering what happened to the French bit, it voted to remain with France in a distinctly dodgy referendum. It later became independent as Djibouti in 1977.)

The new country, informally known as Somalia, had a difficult history: nine years of democracy ended in a coup, and were followed by the 22 year military dictatorship under the presidency of General Siad Barre. In 1991, under pressure from rebel groups including the Hargeisa-based Somali National Movement (SNM), Barre fled, and his government finally collapsed. So, in effect, did the country.

For one thing, it split in two, along the old colonial boundaries: the local authorities in the British portion, backed by the SNM, made a unilateral declaration of independence. In the formerly Italian south, though, things collapsed in a rather more literal sense: the territory centred on Mogadishu was devastated by the Somali civil war, which has killed around 500,000, displaced more than twice that, and is still officially going on.

Somalia (blue) and Somaliland (yellow) in 2016. Image: Nicolay Sidorov/Wikimedia Commons.

The north, meanwhile, got off relatively lightly: today it’s the democratic and moderately prosperous Republic of Somaliland. It claims to be the successor to the independent state of Somaliland, which existed for those five days in June 1960.

This hasn’t persuaded anybody, though, and today it’s the only de facto sovereign state that has never been recognised by a single UN member. Reading about it, one gets the distinct sense that this is because it’s basically doing okay, so its lack of diplomatic recognition has never risen up anyone’s priority list.

Neither has its library.

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Rageeh Omar described the site of the new library in his fundraising video. It occupies 6,000m2 in the middle of Hargeisa, two minutes from the city’s main hospital, 10 from the presidential palace. In one sequence he stands on the half-completed building’s roof and points out the neighbours: the city’s main high street, with the country’s largest shopping mall; the Ministry of Telecoms that lies right next door.

This spiel, in a video produced by the project’s promoters, suggests something about the new library: that part of its job is to be another in this list of landmarks, more evidence that Hargeisa, a city of 1.5m, should be recognised as the proper capital of a real country.

But it isn’t just that: the description of the library’s function, in the government’s Strategic Plan 2013-2023, makes clear it’s also meant to be a real educational facility. NGOS, the report notes, have focused their resources on primary schools first, secondary schools second and other educational facilities not at all. (This makes sense, given that they want most bang for their buck.)

And so, the new building will provide “the normal functions of public library, but also... additional services that are intentionally aimed at solving the unique education problems of a post conflict society”. It’ll provide books for a network of library trucks, providing “book services” to the regions outside Hargeisa, and a “book dispersal and exchange system”, to provide books for schools and other educational facilities. There’ll even be a “Camel Library Caravan that will specifically aim at accessing the nomadic pastoralists in remote areas”.

All this, it’s hoped, will raise literacy levels, in English as well as the local languages of Arabic and Somali, and so boost the economy too.

As described. Image courtesy of Nimko Ali.

Ahmed Elmi, the London-based Somali who’s founder and director of the library campaign, says that the Somaliland government has invested $192,000 in the library. A further $97,000 came from individual and business donors in both Hargeisa and in the disaspora. “We had higher ambitions,” Elmi tells me, “but we had to humble our approach, since the last three years the country has been suffering from a large drought.”

Now the scheme is moving to its second phase: books, computers and printers, plus landscaping the gardens. This will cost another $175,000. “We are also open to donations of books, furniture and technology,” Emli says. “Or even someone with technical expertise who can help up set-up the librarian system instead of a contemporary donation of a cash sum.” The Czech government, in fact, has helped with the latter: it’s not offered financial support, but has offered to spend four weeks training two librarians.  

Inside the library.

On internet forums frequented by the Somali diaspora, a number of people have left comments about the best way to do this. One said he’d “donated all my old science and maths schoolbooks last year”. And then there’s this:

“At least 16 thousand landers get back to home every year, if everyone bring one book our children will have plenty of books to read. But we should make sure to not bring useless books such celebrity biography books or romantic novels. the kids should have plenty of science,maths and vocational books.”

Which is good advice for all of us, really.


Perhaps the pithiest description of the project comes from its Facebook page: “Africa always suffers food shortage, diseases, civil wars, corruption etc. – but the Somaliland people need a modern library to build a better place for the generations to come.”

The building doesn’t look like much: a squat concrete block, one storey-high. But there’s something about the idea of a country coming together like this to build something that’s rather moving. Books are better than sovereignty anyway.

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and also has a Facebook page now for some reason. 

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