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In Dutch politics, the right-ish parties are in favour of more roads, whereas the left-ish parties are against more roads. Although I'm more left-oriented, I disagree with their reasoning. They want to invest in public transport for a better environment. They argue that more roads will lead to more cars, causing even more traffic jams than before. This reasoning sounds rather silly to me. What does science/research say about whether more roads will lead to a better traffic flow?

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    That is actually not necessarily silly. There is an economic mechanism called induced demand that would fit, but I am not knowledgeable enough about that. There have also been known instances where building a new road to alleviate congestion caused motorists to "abandon" several older roads making the new road even worse than the old ones ever were. That has actually been modelled mathematically, but claiming that it would apply to any given situation is stretching facts even more than Fox News is capable of. – Jyrki Lahtonen Feb 25 '17 at 11:41
  • Anyway, the first Google hits relevant to your question pointed at articles that cannot be called scientific. Caveat reader. – Jyrki Lahtonen Feb 25 '17 at 11:42
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    A larger road network with faster speed limits encourages urban sprawl by inducing people to move to suburbs more distant from their jobs, and, more generally, to be more likely to plan longer trips in their cars. This results in more cars on the road. Look at Los Angeles and Atlanta. Of course, other factors in the Netherlands, such as greater attention to urban planning and the significantly higher cost of fuel, may make these examples less applicable. – phoog Feb 25 '17 at 15:58
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    The paper wasn't published because it was TOO obvious to publish? Request for papers if off-topic? I don't even know to respond to that...You are effectively saying you only want anecdotal evidence and no peer reviewed research. OK. I drove to Amsterdam in Nov 2016 and I was in a traffic jam lasting two hours on the A2. Done. Road widening clearly didn't work. – Venture2099 Feb 25 '17 at 19:10
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    Added an answer that covers How could, responsibly, more roads/lanes lead to less traffic jams. Felt it was needed, because althought the accepted answer does cover why just building more roads doesn't sustainably reduce it in the long period, it doesn't cover "how" could it work sustainably. – CptEric Feb 27 '17 at 11:25
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TL;DR No. Roads do not lead sustainably to less traffic jams. In the extreme short term they can do but it can be disastrous for the rest of the traffic network and they increase congestion in the long term through induced demand. Almost all peer-reviewed studies about actual traffic networks across the world in every continent reach the same conclusions.

Evidence

The rule of induced demand says widening highways and adding roads does not ease congestion, and often makes it worse.

In 2009, two economists—Matthew Turner of the University of Toronto and Gilles Duranton of the University of Pennsylvania—decided to compare the amount of new roads and highways built in different U.S. cities between 1980 and 2000, and the total number of miles driven in those cities over the same period.

“We found that there’s this perfect one-to-one relationship,” said Turner.

If a city had increased its road capacity by 10 percent between 1980 and 1990, then the amount of driving in that city went up by 10 percent. If the amount of roads in the same city then went up by 11 percent between 1990 and 2000, the total number of miles driven also went up by 11 percent. It’s like the two figures were moving in perfect lockstep, changing at the same exact rate.

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.

This is reflected in global traffic initiatives

China

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.

Spain

Distinguishing between traffic generated exclusively from the expansion of the road network (induced demand) and that resulting from other demand factors is of crucial importance to properly designed transport policies. This paper analyzes and quantifies the induced demand for road transport for Spain’s main regions from 1998 to 2006, years that saw mobility in Spain attain its highest growth rate.

United States

Empirical evidence of Induced Traffic

Disparate evidence indicates that the provision of extra road capacity results in a greater volume of traffic. The amount of extra traffic must be heavily dependent on the context, size and location of road schemes, but an appropriate average value is given by an elasticity of traffic volume with respect to travel time of about −0.5 in the short term, and up to −1.0 in the long term. As a result, an average road improvement has induced an additional 10% of base traffic in the short term and 20% in the long term: individual schemes with induced traffic at double this level may not be very unusual, especially for peak periods. Induced traffic is particularly seen on the alternative routes that road improvements are intended to relieve.

Europe

Traffic Forecasts Ignoring Induced Demand: a Shaky Fundament for Cost-Benefit Analyses

Although the phenomenon of induced traffic has been theorized for more than 60 years and is now widely accepted among transport researchers, the traffic-generating effects of road capacity expansion are still often neglected in transport modelling. Such omission can lead to serious bias in the assessments of environmental impacts as well as the economic viability of proposed road projects, especially in situations where there is a latent demand for more road capacity.

Australia

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).

Why is this?

The reasoning is because of the fundamental rule - New roads will create new drivers, resulting in the intensity of traffic staying the same.

This is argued in detail in the following peer reviewed scientific study The Fundamental Law of Road Congestion: Evidence from US cities published in the American Economic Review, American Economic Association, vol. 101(6), pages 2616-52, October and in the National Bureau of Economic Research.

It can actually be the that reverse is true. Removing traffic lanes has no adverse effects and leads to greater adoption of public transport.

San Francisco removed a highway section, called the Central Freeway, that carried nearly 100,000 cars per day in 1989. The boulevard that replaced it now only carries around 45,000 daily cars and yet they move.

Civil engineers liken traffic to a gas: It expands to fill the space provided. As civil engineer and sustainability advocate Charles Marohn so eloquently put it, “Trying to solve congestion by making roadways wider is like trying to solve obesity by buying bigger pants.”

Refuting Evidence

Refuting evidence is covered in the academic research above and soundly shown to be biased and short termist in nature. However, a cited academic study can be found here.

The debate that expenditure on new or existing roads induces more traffic has intensified during the 1990s in most developed countries. In this paper the controversy is readdressed from a UK perspective, using the method of Granger noncausality. Results indicate that aggregate expenditure on new and existing roads does not induce additional traffic in the Granger sense. Conversely, the results found that traffic Granger causes road expenditure. The importance of these results, along with issues concerning the selection and specification of dynamic models, are discussed.

However that report was widely rebutted by a subsequent investigation which directly refuted it.

A recent article by Prakash et al. (Applied Economics, 33, 1579–85, 2001) asserted that induced travel effects do not occur. This paper is criticized on several grounds. It disregards much of the recent work in this area that has empirically estimated induced travel relationships. The models specified are inappropriate for properly addressing this question, both in their use of road expenditure data (based on a misunderstanding of how this may relate to traffic growth) and specification of a model that does not account for other variables that generally have a large effect on traffic growth (notably population and income growth). The evidence in the literature is summarized and an analysis of UK road expenditure data shows that expenditure is not a good measure of actual road capacity that is built.

This wired article researching traffic in Texas indicates that the published research may be wrong.

Two things might explain why the Dallas project worked. The first is that the bottleneck on that highway was a very specific problem: a two-lane stretch connecting three-lane highways. Opening the shoulders eliminated the choke points of squeezing into a tighter space. The second and more cynical explanation for the project’s success is that it wasn’t actually successful. The traffic numbers published this month include just a few days after the new lanes opened in September. Traffic has increased since then, though the TxDOT says traffic is still moving faster than before the project. It’s quite possible unbearable congestion will return, as more locals change their behavior to take advantage of what is suddenly a smooth ride—that’s the fundamental principle of induced demand.

Rebuttal Summary

By exaggerating the economic benefits of road capacity increase and underestimating its negative effects, omission of induced traffic can result in overallocation of public money on road construction and correspondingly less focus on other ways of dealing with congestion and environmental problems in urban areas.

Weakest Link

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.

Conclusion

The majority of published research holds that adding lanes or roads makes congestion worse. All of the information supporting road addition and widening is drawn from governmental sources from the departments responsible for spending the money on the transport initiative. Few peer-reviewed, academic studies support road-widening or addition as a positive measure for traffic congestion and easing.

More info here, here and here.

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Yes and No

Many answers already cover part of this, so i won't enter in detail in the data. This answer covers how one does reduce traffic jams with more roads/lanes, with an efficient design and better infrastructure.

Scientific papers prove that more lanes and more highways create induced demand, both by creating a faster and personal alternative to public transport and by allowing citizens living in the expensive, crowded areas to move to less expensive, almost countryside areas.

Road data also shows, thought, that removing or leaving lanes "as they are", without providing any alternative system of transportation, leads to bigger jams, the best examples coming to any city near you without a responsible infrastructure design®

The problem can not be resolved with either the not doing anything! build some cycling lanes to satisfy at least some voters!, or build more lanes! more roads! more highway tolls! politics.

The problem of road networks in western Europe is directly related to bottlenecks provided by traffic, and unexisting or overexpensive alternatives. It doesn't matter how many lanes you build from city A to city B. If city B's main road has a 100 vehicle / minute capacity, it'll stay that. 8 lanes going into 2 lanes instead of 4 lanes into 2 lanes will just piss twice the amount of people in the same amount of time.

Let's see a graphic example:

enter image description here

No matter how many lanes we add to the left side, if the right side stays the same, nothing will change.

To correctly reduce traffic jam numbers AND fight induced demand, its cities and regions must have a working and functioning transport infrastructure that is designed to provide different efficient transportation methods from A to B.

First rule of transportation: not every citizen is suited for non-mass transportation.

Parents with kids that study in different schools and do extra curricular activities, retired/old people, tourists, businessmen have a lot of valid reasons to still need to use a private or at least massive transportation system, so we cannot rely solely on bicycle transportation methods for those, still, we must provide those that can rely on them (young people, average commuters living not that far from the office, teenagers ... )

An efficient bicycle transportation network will connect cities, neighborhoods, and business hubs seamlessly without severely interrupting the non-bike traffic. That means that i should be able to drive back and forth from my home to the nearest hub to my desired location without ever having to step into the sidewalk or the road.

enter image description here

Mass transportation alternatives to private transportation must be provided, that should be interconnected and must be a cheap alternative to the private owned ones.

If we provide of a good and affordable Train, Bus and Metro infrastructure to our citizens, less will require private transportation.

Good example of an imaginary town A 50km away from city B:

I get out of home at 7:00, walk 10min to my nearest bus station, where a bus stops every 15min.

I check in my monthly commute 30€ ticket, the bus stop on the neighborhood tram station by 7:25, where there is a tram every 10 min, with enough time to pick the 7:30 commute train that also works with the same monthly ticket, and that stops all along the city's business hubs.

I stop by 7:50 at the nearest station to my workplace, walk 1-5min depending on traffic and get there on time.

Bad example of a current existing city A 110km away from city B:

I leave my home at 6am, and walk for 30/40 minutes to the local train station, because there isn't any bus line that could leave me there in time. I purchase a 30€ back-and-forth single ticket on the cheapest fast train, that has an average frequency of one every 2.5 hours.

I get to the city B central station 1h 15min later, where i must purchase a single 2.99€ metro ticket.

The metro has a frequency of 5min, but is not connected to my workplace line (C), so i must exit the metro, walk for 10 minutes, then wait for the workplace line's inexplicable 10min long frequency, and also pay 2.99€ again, because there's no commute bonuses.

I finally get to my workplace, having spent twice the time it takes to do the same trip on a private car, and one and a half car diesel deposit in €, per day.

This example is taken from my personal experience visiting Barcelona once in a while®, and can vary from country to country.

Second rule of transportation: the effort to not use private means of transportation is proportional to the cost in time and the cost in money of the commute.

How does one fix this?

Victoria, Australia's infrastructure improvements go all the way with my reasonings, this video is the perfect example:

Swan bridge improvement

Chandler Highway upgrade

Finally, my conclusion:

A transportation network is like a computer. Every component is essential for its speed. If you have a flaw or a uncared component, the whole system will slow down as a result.

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    The "Good Example" has a travel time of 51-55 minutes for 50 km, and includes 11-15 minutes exposure to potential rain and other bad weather. I won't call that "good." – Sjoerd Feb 27 '17 at 13:33
  • it's good, not "best" or "excellent". it can always be better. – CptEric Feb 27 '17 at 13:54
  • it's actually a quite decent commute time and exposure compared to the average commute time in Barcelona or berlin, adding finding a parking spot + parking price + then walking to the workplace – CptEric Feb 27 '17 at 14:01
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    @Sjoerd In the US, most commutes like the "good" example would be a 25 minute drive home to work, even fighting congestion, which is why so many people drive. – Andy Feb 27 '17 at 23:55
  • again, depends on context and distance. Without congestion, my 17km commute is done in 10 minutes. With some congestion, around 20. with severe, 35.by bus is 20min, so only on congestion days it would be necessary. But my friend's commute in barcelona is 1 and a half hours by car and 45min by train with normal congestion, due to the many bottlenecks, the only thing stopping him from taking the train everyday is the severely bad conditions spain's trains have, tend to break a lot mid-commute. – CptEric Feb 28 '17 at 7:08
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No matter what academic research may say, it has to deal with experiences from real life. And when dealing with the political debate in The Netherlands, one has to be aware of the real life experience we have had in The Netherlands, as it certainly will be used in a political debate.

The real life experiments from a change in government policy after the 2006 elections strongly suggests that adding lanes does work under certain circumstances.

The A2 is the clearest example.

The A2 (Amsterdam - Utrecht), the major North-South highway, was expanded from 3 lanes each way to 5 lanes. Traffic congestion on this part of the A2 almost completely disappeared as a result.

This was part of a new government policy after elections, so many roads were widened during those years, not just the A2. This might have helped reducing induced traffic and other side-effects.

There are also examples of small improvements that didn't help, e.g. the A4 where parts were widened to three lanes each way, leading to more traffic jams on the choke points where it went back to two lanes.

Some other major congested roads couldn't be widened due to space restrictions. Those drifted to the top of the top-50.

Academic research likely has helped to pick the right spots to be improved.

It is without doubt that in the long term - e.g. by 2050 - the current situation will not be good enough. But until that moment arrives, many people will have benefited from the short term positive effects. Keeping a network up to date will always be work-in-progress, and will never be finished.


Links (in Dutch):


From the VID links I used above ( http://www.vid.nl/top50.2016.html ), the total congestion for all roads:

2006: 14573500
2007: 15713022
2008: 15452236
2009: 13215678
2010: 13751244
2011: 10437738
2012:  8766086
2013:  8040298
2014:  7956449
2015:  9824126
2016: 10931110

Of course, there has been a major recession in those years, clearly visible in the numbers. Still, 2016 is significant lower than all years before the recession, while by now the economy is supposed to have recovered.

The usual explanation for the difference between 2006 and 2016 is that it's due to the many road works started after the elections of 2006. As the part of government responsible states:

In de jaren 2005-2015 is het reistijdverlies op het hoofdwegennet met 1 procent gedaald. Aanleg van extra rijstroken heeft voor het grootste deel bijgedragen aan deze afname van het reistijdverlies op het hoofdwegennet over deze periode.

Translated:

From 2005-2015, travel time loss on the major road network has been reduced by 1 procent. Adding additional lanes contributed for the largest part to this reduction of time travel loss on the main road network over this period.

Note that means that the policy of adding lanes was able to negate the effects of traffic growth by both induced traffic and population growth over this period of 10 years.


My observation:

After this Real Life experiment, there isn't much discussion anymore in The Netherlands whether road widening helps in certain cases. In politics, Real Life Experiences trump academic papers.

Nowadays, political debate in The Netherlands has shifted to discussion of what is to be sacrificed, e.g. the number of trees to be chomped down or what route.

As an example, the PvdA (Labour) program for the upcoming elections doesn't contest that it might be necessary to widen roads in some cases:

The PvdA is in favor of good accessibility, also by car. We therefore support the construction of new roads and widening of roads if it is evident that this traffic engineering is necessary and provided that damage to nature and the environment is limited. [..]

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They argue that more roads will lead to more cars,

Both sides are correct.

One party argues that if you expand roads, but the traffic in amount of vehicles being constant, you get less congestion -> you only need common sense to agree to that.

The other side argues that if you expand roads, you encourage private ownership of cars, and increase the likelihood of those cars to eventually congregate to one area (city rush hours, stadiums, concerts, major shopping centers, etc.), you get congestion. ie. you never have "the amount of vehicle being constant".

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