Can Really Build More Roads Improvement Traffic?

They are election dates in Spain and many politicians insist on fixing problems of congestion with more cars, more tracks. In general, this not resolves the situation, but it gets worse: is creates demand induced and them jams return to them few months. We translate an article from The Conversation, made by Matthew Beck and Michael Bliemer of the University of Sydney, which explains this issue in more detail. If in your city want to build more expressways, remind them that that does not solve congestion, only postponed it.

Translated with permission from The Conversation – thank you, Khalil!

Of really building more roads improves the traffic?

Matthew Beck and Michiel Bliemer, University of Sydney

The jams are a great source of frustration to them users of roads and have worsened with the time in the greater part of cities. Is have proposed different solutions, as implementation rates by congestion (favorite of them economists of the transport) or invest in transport public. The solution that applies more frequently is to build more roads, but does this approach?

A recent study in the United States points to Los Angeles, Honolulu and San Francisco as cities with more traffic jams in this country. All these towns trust your transportation solutions citizen, almost exclusively, to highways.

Although China has made grow 16.300 Km motorway network in 2000 to about 70,000 Km in 2010, the average time of journey to work in Beijing during 2013 was 1 hour and 55 minutes, 25 minutes more than the previous year.

Why, then, the residents of these cities, all with huge amounts of capacity available in their roads, not inhabit in a utopia of it driving?

Induced demand

The first concept that must meet is called demand induced.

Think of the street where you live. If a new highway makes that you can drive to work in less time, you can you benefit you, but this same work time reduction can make two other residents of your street begin to drive; and other two in the street of to the side; and another two in the next Street, etc. In a very short time, the way to work costs the same time as always.

In transport, this response, well established, is known in several contexts as the paradox Downs-Thomson, the paradox Pigou-Knight-Downs or the position of Lewis-Mogridge: a new road can relieve to them drivers of part of the congestion to short term, but almost all the benefit is lose to long term.

The project WestConnex of Sydney. Image of the Draft Metropolitan Plan for Sydney.

More even, although some way can solve the congestion local, to the have more traffic in the network of roads the congestion can move is to another site. In Sydney, for example, the road WestConnex can have improved the traffic in Parramatta Road, but worsen the jams in the city.

The weakest links

The congestion it determine those links more weak in the network of roads. If the expansion of the capacity not extends these links, that make of neck of bottle, them jams could simply move is to another part of the network without resolve the problem of congestion. And worse still, could create traffic jams even worse.

The paradox of Braess is a famous example in which the construction of new roads in the location wrong can carry to worsen them times of travel for all, even without exist demand induced, because them new roads can take to more drivers to them links more weak of it network. And the reverse can also occur: eliminate roads can improve the traffic conditions.

This paradox occurs because each driver choose the route that you is more fast without have in has them implications that his election has in others drivers. Them bikers only is concerned of the amount of vehicles that are by in front of them in the row of the traffic and les dan equal which come by back. Is a problem classic of theory of games, very similar to those studied John Nash when received the prize Nobel.

Build, expand or duplicate motorways or dual carriageways can induce more people to drive their cars instead of using public transport. Image of AAP / Dean Lewins.

What they say the data?

A U.S. study shows a strong relationship between the kilometers built new highways and the total kilometres travelled in cities of the United States, a finding that the authors call “the fundamental law of the congestion on the roads”.

Similar relations in Spain and elsewhere in the United States, where also the major capacity expansions have achieved very little or no reduction in network traffic densities have been found. Also is has found in Europe, where ignore the demand induced has carry biases to the estimate the impacts environmental and the viability economic of some projects of roads.

The new Premier of new South Wales, Mike Baird, promised in his campaign for re-election more roads and less traffic.

There is similar evidence about the traffic that crosses the Bay in Sydney . The bridge of the Bay of Sydney bore a volume of traffic stable of approximately 180,000 vehicles / day between 1986 and 1991. Sydney Bay Tunnel opened in 1992, and the total volume of traffic that crosses the Bay increased in 1995 to almost 250,000 vehicles per day. This 38% of increase in the traffic can be attributed is to the demand induced and not to the growth in the population, that was approximately of the 4% during these years.

Others examples empirical confirm the existence of the paradox of Braess. For example, in 1969 was built a new road in Stuttgart, Germany, that not improved the conditions of the traffic. And after closing the road, jams decreased.

There have been similar cases in which the closure of a highway meant better traffic conditions in New York, where the closing of 42nd Street (until then an artery to traverse Manhattan) meant that traffic was significantly less congested than the average of NY.

A recent pilot study confirmed the existence of the paradox, showing that the capacity expansion can mean worst traffic conditions for all.

Induced demand theory is accepted by a large majority, but not by all. For example, the authors of a article of 2001 argue that the demand induced not exists. However, Goodwin and Noland, of the United Kingdom, researchers have been critics of this study.

If considered separately, the construction of new roads can certainly improve the traffic. But these effects may only be short-term and local. Congestion may be worse in other parts of the network, and experience shows that the overcapacity existing in the network is quickly filled with more cars.

Even without them new users that create them new roads, if is built in places wrong, the new way can worsen the congestion simply by the way in that it people is behaves. Roads, by themselves, do not solve congestion in the long run: are only a tool (problem) more than that can be used for the management of the transport.

 

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