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.

 
 
 
 

Two east London boroughs are planning to tax nightlife to fund the clean up. Will it work?

A Shoreditch rave, 2013. Image: Getty.

No-one likes cleaning up after a party, but someone’s got to do it. On a city-wide scale, that job falls to the local authority. But that still leaves the question: who pays?

In east London, the number of bars and clubs has increased dramatically in recent years. The thriving club scene has come with benefits – but also a price tag for the morning clean-up and cost of policing. The boroughs of Hackney and Tower Hamlets are now looking to nightlife venues to cover these costs.

Back in 2012, councils were given powers to introduce ‘late night levies’: essentially a tax on all the licensed venues that open between midnight and 6am. The amount venues are expected to pay is based on the premises’ rateable value. Seventy per cent of any money raised goes to the police and the council keeps the rest.

Few councils took up the offer. Four years after the legislation was introduced, only eight local authorities had introduced a levy, including Southampton, Nottingham, and Cheltenham. Three of the levies were in the capital, including Camden and Islington. The most lucrative was in the City of London, where £420,000 was raised in the 2015-16 financial year.

Even in places where levies have been introduced, they haven’t always had the desired effect. Nottingham adopted a late night levy in November 2014. Last year, it emerged that the tax had raised £150,000 less than expected in its first year. Only a few months before, Cheltenham scrapped its levy after it similarly failed to meet expectations.


Last year, the House of Lords committee published its review of the 2003 Licensing Act. The committee found that “hardly any respondents believed that late night levies were currently working as they should be” – and councils reported that the obligation to pass revenues from the levy to the police had made the tax unappealing. Concluding its findings on the late night levy, the committee said: “We believe on balance that it has failed to achieve its objectives, and should be abolished.”

As might be expected of a nightlife tax, late night levies are also vociferously opposed by the hospitality industry. Commenting on the proposed levy in Tower Hamlets, Brigid Simmonds, chief executive at the British Beer and Pub Association, said: “A levy would represent a damaging new tax – it is the wrong approach. The focus should be on partnership working, with the police and local business, to address any issues in the night time economy.”

Nevertheless, boroughs in east London are pressing ahead with their plans. Tower Hamlets was recently forced to restart a consultation on its late night levy after a first attempt was the subject of a successful legal challenge by the Association of Licensed Multiple Retailers (ALMR). Kate Nicholls, chief executive at the ALMR, said:

“We will continue to oppose these measures wherever they are considered in any part of the UK and will urge local authorities’ to work with businesses, not against them, to find solutions to any issues they may have.”

Meanwhile, Hackney council intends to introduce a levy after a consultation which revealed 52 per cents of respondents were in favour of the plans. Announcing the consultation in February, licensing chair Emma Plouviez said:

“With ever-shrinking budgets, we need to find a way to ensure the our nightlife can continue to operate safely, so we’re considering looking to these businesses for a contribution towards making sure their customers can enjoy a safe night out and their neighbours and surrounding community doesn’t suffer.”

With budgets stretched, it’s inevitable that councils will seek to take advantage of any source of income they can. Nevertheless, earlier examples of the late night levy suggest this nightlife tax is unlikely to prove as lucrative as is hoped. Even if it does, should we expect nightlife venues to plug the gap left by public sector cuts?