Without getting back on the topic of pohutukawas or St Luke’s Road again, I did notice something funny in the statement that Greg Edmonds, Auckland Transport’s Chief Operating Officer, made in Metro Magazine in response to the issue:
The founding premise of the Auckland super city was that the city’s congestion was costing $1 billion a year in lost productivity and this had to change.
Auckland Transport (AT) was created to solve the congestion problem…
Some people might think that this is a slightly too narrow view of Auckland Transport’s mandate. Whatever. Fair enough.
However, there is actually a much more serious problem with Mr Edmonds’ comments. Simply put: the notion that we can “solve the congestion problem” is not at all realistic. (Unless we are willing to try out road pricing, which is unlikely given the tepid response to the last few studies of the issue.)
I don’t want to pick on Mr Edmonds in particular. It’s common to hear politicians, bureaucrats, and advocates from all over say similar things. We constantly hear that Project X or Project Y will “fix congestion” or “solve gridlock” or “save us [some unthinkably large amount of money] in congestion costs”.
As an economist, I’m baffled by these statements. The empirical evidence on congestion overwhelmingly shows that it is not possible to reduce it by building more roads. This is because people change their behaviour in response to bigger roads. They shift from walking to the store to driving there; they buy a house further out of town; they travel at different times.
Here’s what two North American economists, Duranton and Turner, had to say on the topic after undertaking a comprehensive, multi-decade study on induced traffic in US cities:
Our data suggests a ‘fundamental law of road congestion’ where the extension of most major roads is met with a proportional increase in traffic. Not only do we provide direct evidence for this law, but also show find evidence that three implications of this law; near flat demand curve for VKT, convergence of traffic levels, and no effect of public transit on traffic levels.
All earlier studies, such as this comprehensive 1998 study of 70 US metro areas over a 15 year period cited by walkable city advocate Jeff Speck, have come up with identical findings:
Metro areas that invested heavily in road capacity expansion fared no better in easing congestion than metro areas that did not. Trends in congestion show that areas that exhibited greater growth in lane capacity spent roughly $22 billion more on road construction than those that didn’t, yet ended up with slightly higher congestion costs per person, wasted fuel, and travel delay.
Consequently, all we can realistically do about congestion is to give people good alternatives to participating in it. Other modes, such as grade-separated rapid transit and walking and cycling, do not get congested in the same way as roads do. While the research shows that providing alternatives to driving does not necessarily reduce road congestion, it does give people a way to reduce their exposure to it.
In light of these fundamental economic realities, it is essential that transport agencies stop talking about “fixing congestion”. This is nothing more than a dangerous fantasy.
Suggesting that we can solve congestion creates unrealistic hopes among the public. Every time a politician or transport agency opens a new road and promises that it will reduce congestion or speed up people’s journeys, they are feeding expectations that can never fully be met.
The result of this is that transport agencies are constantly dealing with demands for more roads that will not actually deliver long-term solutions to the problem of congestion. This sets the transport profession up to constantly fail to satisfy people’s desires and demands. This has to be a tremendously disheartening situation to be in.
My personal view is that instead of talking about “fixing congestion”, transport agencies should instead promise to deliver outcomes that are actually achievable.
This could include, for example, committing to deliver transport choice to underserved areas of the city by investing in rapid transit infrastructure, frequent bus services, and safe walking and cycling infrastructure. While transport agencies would have to work hard to deliver on all this, they could expect that the end result would be more transport choice for residents.
Transport agencies could even commit to some traditionally roads-centric goals, like, say, building new roads to enable the development of a new subdivision at the edge of the city. At least, as long as they weren’t making unrealistic promises of fast, frictionless commutes to the future residents…
Proponents of driverless cars often suggest the technology will make all sorts of significant changes to transport. Gone will be car ownership with people just hiring a car when they need one, like taxi’s only easier and cheaper. As such they say gone too will be the need for public transport, especially when you take away some of the benefits PT currently has like being able to do other things such as work, read, use a phone or even sleep. Further congestion will also be a thing of the past with these smart vehicles able to better work together rather than the randomness of humans. Of course the biggest and likely most accurate prediction will be safety as for a start these cars will obey the road rules so no speeding, no running red lights or any of the other bad habits human drivers have.
That all sounds wonderful however an article from CityLab highlights research showing that at least for some time driverless cars could actually make things worse on the roads.
A new simulation-based study of driverless cars questions how well these two big secondary benefits—less traffic and more comfort—can coexist. Trains are conducive to productivity in large part because they aren’t as jerky as cars. But if driverless cars mimic the acceleration and deceleration of trains, speeding up and slowing down more smoothly for the rider’s sake, they might sacrifice much of their ability to relieve traffic in the process.
“Acceleration has big impacts on congestion at intersections because it describes how quickly a vehicle begins to move,” Scott Le Vine of Imperial College London, who led the research, tells CityLab via email. “Think about being stuck behind an 18-wheeler when the light turns green. It accelerates very slowly, which means that you’re delayed much more than if you were behind a car that accelerated quickly.”
For their study, Le Vine and colleagues simulated traffic at a basic four-way urban intersection where 25 percent of the vehicles were driverless and the rest were standard. In some scenarios, the driverless cars accelerated and decelerated the way that light rail trains do—more comfortable than, say, riding in a taxi, but still a little jerky at times. In other scenarios, the cars started and stopped with the premium smoothness of high-speed rail.
Within these broad scenarios the researchers also tested alternatives that reduced speeds but improved smoothness, such as longer yellow lights or following distances. All told they modeled 16 scenarios against a baseline with all human-driven cars. The researchers then ran each simulation for an hour, repeated it 100 times, and calculated the average impact that scenario had in terms of traffic delay and road capacity.
In every single test scenario, driverless cars designed to create a comfortable, rail-style ride made congestion worse than it would have been in a baseline scenario with people behind every wheel.
So cars with fast acceleration and deceleration are obviously easy to make but that’s not what people are likely to want if you’re also trying to do some of the other activities mentioned earlier. Regardless traffic generally moves at the pace of the slowest vehicles so all it takes is one slow driver or driverless vehicle and many others will be slowed down too. I bet they won’t say that in the marketing brochures.
The interior of the Mercedes-Benz driverless car concept
I suspect this isn’t the only aspect of driverless cars that could create congestion. As an example the driverless taxi model that most people say will happen, is likely to result in a lot more vehicle movements as cars reposition themselves to pick up additional fares. That means that where roads are generally congested in one direction only, with driverless cars congestion could occur in both directions.
Earlier this week, I took a look at the relationship between congestion and density. I was investigating geographer Phil McDermott’s claim, based on some dodgy data comparing between cities, that increasing density would increase congestion.
Economists know that it is difficult to make inferences about causality using cross-sectional analysis. Simply looking at variations between different cities doesn’t allow you to form robust conclusions about how those cities got to where they are.
One of the ways in which economists seek to strengthen their understanding of causality is to look at changes over time. For example, if you observe that increases in density tend to be followed by increases in congestion, then that is stronger (although not necessarily conclusive) evidence that there is a causal relationship.
With that in mind, it is worth asking: How have congestion and density changed in New Zealand cities over time? Unfortunately, we don’t have enough data points to conduct a robust econometric analysis, but we do have enough to start painting a picture of recent changes. We can draw upon two relevant sources:
I’m going to focus on NZ’s three largest cities – Auckland, Wellington, and Christchurch – as two of the three experienced big increases in density between 2001 and 2013. (MoT hasn’t collected data on Hamilton and Tauranga for as many years.) If these increases in density coincided with rising congestion, it may be an indication that intensification can lead to increased congestion.
Here’s the data. It shows that density has risen 33% in Auckland between the 2001 and 2013 Censuses, 17% in Wellington, and a mere 3% in Christchurch:
And here’s the Ministry of Transport’s Congestion Index, which measures the average minutes of delay per vehicle-kilometre, relative to totally free-flowing conditions. This is a bit of an unrealistic comparison, as a 2013 NZTA research report by Wallis and Lupton shows. The only way that you can totally avoid all queuing or stopping at traffic lights is if there are no other cars on the road. So it wouldn’t be realistic to say that we could speed up the average Auckland trip by half a minute per kilometre. However, this is still a useful indicator for changes from year to year.
While the Index bounces around a bit from year to year, the overall trends are clear. Levels of congestion are flat or falling in Auckland and Wellington, which experienced big increases in density over the last decade, and rising in Christchurch, which hasn’t gotten denser. In particular:
- Average delay for Auckland drivers was 25% lower in 2013 than it was in 2003
- Average delay for Wellington motorists fell 5% from 2004 to 2013
- Average delay for Christchurch drivers rose a staggering 31% between 2004 and 2010. Unfortunately, MoT’s monitoring seems to have been disrupted by the earthquake, but anecdotal evidence suggests that congestion has worsened since then.
In short, data on changes in density and congestion in New Zealand cities contradicts the notion that intensification will necessarily cause worse traffic congestion. If anything, it suggests that rising density may do the opposite, by making it more feasible for people to walk, cycle, or take public transport.
Do we need to treat this data with caution? Most certainly. As I noted earlier in the week, there are a number of omitted variables that influence congestion, such as such as changing consumer preferences, macroeconomic changes, and significant investments in both roads and public transport over the last decade. But it does suggest that wild claims about the negative traffic impacts of new apartment buildings should be taken with a significant grain of salt.
What do you make of this data?
A number of recent posts have taken a look at some of the “strategic misrepresentations” that people have used to argue for a sprawled-out, roads-focused Auckland. We’ve taken aim at some of the common fallacies, including:
A while back someone sent me an article by geographer Phil McDermott that really hits the trifecta of fallacies. He argues that building apartment buildings on arterial roads – precisely where they will have the best access to frequent public transport services on Auckland’s New Network – is a bad idea because it will lead to increased congestion on the roads.
McDermott’s argument is long on subjective judgments (young people may want apartments but old people downsizing from big suburban homes never will!) and short on quantitative analysis. Here’s his key piece of evidence that constructing apartments on arterial roads will inevitably lead to more congestion:
Congestion – the elephant in the apartment
That might be just as well because mindlessly boosting residential development on arterial roads promises simply to compound Auckland’s congestion problems.
We know higher densities are associated with higher congestion. Auckland’s geography means it already performs poorly on this count. The Tom Tom Congestion Index confirms this.
When the 2013 congestion index for 65 American and Australasian cities is plotted against population density (sourced from the Demographia website) Auckland sits among the worst performers – Vancouver, Sydney, Los Angeles, and San Francisco (Figure 2).
Figure 2: Population Density and Congestion
This is not a serious piece of analysis – it is an insult to econometricians. McDermott makes three elementary errors in this short excerpt alone.
First, he uses bad data that misrepresents levels of density and congestion in these cities. Matt has previously taken a look into the guts of the TomTom Traffic Index and found that it is not a useful measure:
It measures the difference in speed between free flow and congested periods. That means cities with lots of all day congestion there isn’t as much of a difference between peak and off peak times and therefore they get recorded as having less congestion.
Likewise, I’ve done some empirical work on population densities in New Zealand and Australian cities that has showed that Demographia’s statistics are similarly meaningless. Demographia measures the density of the average hectare of land in the city, rather than the density of the neighbourhood in which the average person lives. Nick has shown how badly these figures misrepresent the actual density of New Zealand cities:
Second, McDermott omits important variables and makes inappropriate inferences about causality. While he observes a correlation between two variables, that’s hardly sufficient to prove that building apartments will increase congestion. The causality could very easily run the other way. For example, it could be the case that the presence of congestion creates an incentive for people to live closer to employment and amenity. If that’s the case, then McDermott’s preferred policy of banning apartment developments would make Aucklanders much worse off by preventing them from minimising their travel costs.
Another possibility is that the relationship between density and congestion is mediated through other factors. Both may be caused by a third variable that McDermott has omitted, or there may be an intermediate step between density and congestion. (Or, as noted above, the measures themselves might be rubbish.)
A while back, CityLab’s Eric Dumbaugh provided an excellent illustration of the complex nature of congestion. He looks at data on US cities and finds that higher congestion is associated with higher, rather than lower, levels of productivity:
As per capita delay went up, so did GDP per capita. Every 10 percent increase in traffic delay per person was associated with a 3.4 percent increase in per capita GDP. For those interested in statistics, the relationship was significant at the 0.000 level, and the model had an R2 of 0.375. In layman’s terms, this was statistically-meaningful relationship.
Such a finding seems counterintuitive on its surface. How could being stuck in traffic lead people to be more productive? The relationship is almost certainly not causal. Instead, regional GDP and traffic congestion are tied to a common moderating variable – the presence of a vibrant, economically-productive city. And as city economies grow, so too does the demand for travel. People travel for work and meetings, for shopping and recreation. They produce and demand goods and services, which further increases travel demand. And when the streets become congested and driving inconvenient, people move to more accessible areas, rebuild at higher densities, travel shorter distances, and shift travel modes.
In light of these counterintuitive relationships, the simple two-variable OLS regression that McDermott is relying upon is almost certainly misleading.
Third, McDermott fails to recognise that people are less exposed to congestion in denser, mixed-use cities. It’s simple: when people have better transport choices – i.e. access to frequent bus services and rapid transit, and safe walking and cycling networks – it doesn’t matter as much that the roads are congested. Increasing Auckland’s density by constructing apartment blocks and terraced housing on arterial roads will make it easier for people to have those choices, because the arterial roads are where the frequent bus services under the New Network will go:
Frequency is freedom
Furthermore, density allows people to be closer to where they want to go. I find it odd that McDermott (and others) underestimate the importance of physical proximity in cities, even as people are paying high prices for the privilege. Building more homes in the areas that are accessible to jobs and amenities will allow more people to choose proximity over long commutes. (Without preventing others from making a different choice.)
A question for the readers: Would you rather have a 40 kilometre commute travelling at 80 km/hr, or a 5 kilometre commute moving at 30 km/hr? Show your work…
Following the gridlock on the roads last Saturday, the NZ Herald published several perspectives on how Auckland should cope with disruption to its transport networks. Matt weighed in with an excellent piece on the need to build Auckland’s long-awaited rapid transit network, which would give people an alternative to congested roads. However, the Herald “counterbalanced” it with some arrant nonsense about the need for more motorways by University of Auckland associate professor (and prominent climate change denialist) Chris de Freitas.
I use the term “nonsense” for good reason. The article was rife with factual errors that undermined the points that it was trying to make. Let us count the mistakes.
One: Congestion does not cost the Auckland economy billions each year.
De Freitas contends that:
The cost to the region’s economy of traffic delays is estimated to be many billions of dollars a year, which does not include the mental anguish caused to frustrated and angry drivers.
He does not provide any citations for this figure. However, I am aware of the relevant research, including a 2013 NZTA research paper by Wallis and Lupton that found that a more realistic figure for the cost of congestion in Auckland was a mere $250 million:
Including all congestion cost components, we concluded that the costs of congestion in Auckland are approximately $1250 million per year when compared with free-flow conditions, or $250 million per year when compared with the network operating at capacity.
In other words, the only way we could achieve that hypothetical $1.25 billion saving in congestion costs would be to build a network far, far in excess of what is required to move vehicles. Furthermore, Wallis and Lupton’s estimates are derived using NZTA’s Economic Evaluation Manual procedures, which explicitly account for non-monetary values such as travel time and driver frustration. The actual financial costs of congestion are likely to be an order of magnitude lower – i.e. closer to $25-50 million. That’s just not a lot compared to Auckland’s regional GDP of $75 billion.
Two: Auckland is not adding a Dunedin worth of population every 3-4 years.
De Freitas asserts that:
Given that the region’s population continues to expand by the size of Dunedin every three to four years, the vulnerability to traffic snarl-ups will grow exponentially.
According to the most recent Census data, Dunedin has a population of roughly 120,000 people. Between 2001 and 2013, Auckland’s population increased by approximately 255,000 people, or roughly 21,000 people per year. For those who like numbers, that means one new Dunedin every six years, not every three years. De Freitas seems to think that Auckland is growing twice as fast as it actually is.
Furthermore, the Ministry of Transport’s Congestion Index shows that travel time delay actually fell by one-quarter between 2003 and 2013. This contradicts de Freitas’ claim that congestion will increase “exponentially” as population grows – why hasn’t it increased over the past decade?
Three: Rapid transit networks are well-suited for regions with natural choke-points.
De Freitas argues that geography is destiny, and that Auckland’s skinny shape makes it a natural for roads:
Public transport itself will not ease the region’s traffic crisis. Auckland’s geography, history and politics make it a unique case for infrastructure planning. Its long, thin shape led to the earliest transport routes developing along a narrow north-south axis. Strategic arterial roads followed this pattern.
He correctly observes that road networks become less efficient when they are forced through natural choke-points like harbours and portages. However, these choke-points actually make public transport more efficient, not less. Putting more cars on a single road causes congestion and makes that road less efficient, but putting more buses or trains on a single right-of-way increases efficiency by allowing them to share costly infrastructure.
Four: Auckland’s motorway network already has alternative routes.
De Freitas contends that the Auckland motorway network lacks redundancy:
The result is a highway system that is not yet part of a fully integrated network. It is linear with no alternative routes around major bottlenecks. Traffic that would want to bypass the city is forced through Spaghetti Junction, adding to the vulnerability of the system to gridlock.
He has apparently not noticed that NZTA has almost finished building a bypass of Spaghetti Junction at a massive cost of $3.6 billion – the Western Ring Route. Perhaps he hasn’t been out west in the last decade, but if he had he would have noticed the construction of SH18 and the Upper Harbour Bridge, major expansions of the SH16 causeway, and the in-progress construction of the Waterview Connection to link SH16 with SH20.
Do we have to cover the whole region in asphalt to satisfy the man?
Five: A major earthquake in Auckland is extremely unlikely.
De Freitas raises the spectre of a Christchurch-esque quake:
The region’s most strategic arterial roads are vulnerable during earthquakes. Older multi-span bridges and abutments along motorways such as around Spaghetti Junction would be most vulnerable to damage from ground liquefaction. Even minor damage to these would bring city traffic to a halt.
Now, I’m no geologist… but both of my parents are geophysicists who started out researching Auckland’s rocks. They do not believe that Auckland faces serious risks of earthquakes. Volcanoes are a stronger possibility, of course, but volcanic activity doesn’t cause soil liquefaction. Here is a map from the British Geological Survey of every major earthquake in New Zealand since 1843. Notice the total absence of any recorded earthquakes anywhere near Auckland. Unlike Christchurch, we are not close to NZ’s fault lines:
Six: More roads are not a good solution for disaster readiness.
De Freitas argues that more roads are needed to evacuate Auckland:
The vulnerability of a city is to a large extent a function of the adequacy of preparedness planning. How soon could Auckland be evacuated?
There is limited motorway access out of the isthmus that is the Auckland urban area, so there few alternative exits. Main feeder roads head for one major harbour crossing and easily become congested.
Some American cities that are vulnerable to regular natural disasters have tested the “more roads” approach to evacuation. So here is Houston, attempting to evacuate on one of its eighteen-lane freeways during Hurricane Katrina in 2005. Not a lot of people actually made it out of the city:
We could devote endless hectares of increasingly valuable land attempting to repeat the same solution that failed Houston. Or, if we think that natural disasters are a serious risk, we could invest in disaster preparedness and civil defense to ensure that the city’s residents will still have access to food, water, and health care services, regardless of what happens. That’s likely to be a much more practical, cost-effective solution.
Finally: The Herald needs to get better at fact-checking, or print a retraction.
While de Freitas’ article was printed in the op-ed page, that is no excuse for its blatant errors and omissions. Auckland only has one newspaper of record, and its credibility and usefulness to its readers is undermined when it prints this sort of gibberish.
Yesterday large parts of Auckland’s Motorway network was brought to its knees by a single crash.
A serious crash brought Auckland’s motorway network to its knees with motorists stuck in grid-locked traffic for up to four hours.
Three motorbikes and a truck collided on Auckland’s Harbour Bridge about 12pm yesterday, leaving two motorcyclists with critical injuries and a third with serious injuries.
Three northbound lanes were closed while emergency services attended the scene of the crash.
Auckland motorists were stuck in grid-locked traffic, making a normally 40-minute journey from the airport to the North Shore take up to three hours.
The tail of the traffic jam on State Highway 1 stretched from the base of the Harbour Bridge to Highbrook Drive, Otahuhu, before all lanes were re-opened at 3pm.
Traffic on the Northwestern Motorway was very heavy, with motorists diverting trips they’d usually take on the Northern Motorway in an attempt to avoid the snarl up.
Roads throughout Central Auckland were also backed up as motorists tried to get on the motorway and became stuck.
Unfortunately I didn’t get a screenshot but at one stage the motorway traffic map looked like this with a considerable amount of red as well. In addition local roads all around the motorways would have been severely affected too.
While the crash is unfortunate – and I hope those involved are ok – as I say in the article, there is very little that could be done to prevent the ensuing chaos it caused. We’ve seen in recent years the motorway network brought to a standstill numerous times by accidents and this is especially the case when they occur on some of the busiest sections of the network.
I happened to be travelling towards the city about 1½ hours after the Harbour Bridge was reopened and SH16 was still at a standstill all the way from Te Atatu to the city which also showed just how long the delays took to clear.
Yesterday’s incident also shows highlights that even an additional harbour crossing wouldn’t have helped. As people tried to avoid the hold up they flooded to use the North-Western Motorway and that too soon jammed up. With an additional crossing the same thing would have happened as masses of people diverted their trips to avoid the bridge. It’s also worth pointing out that the opening of the Waterview Connection isn’t going to make this any better either as the project is expected to see traffic volumes on the motorway increase. This is due to new trips being generated thanks to the connection as well as a lot of trips shift from local roads on to the motorway network. The result would be even more people stuck in congestion – many deep underground.
So what can we do?
What we need is a comprehensive multi modal network that is able to deliver real choice to Aucklanders in how they get around. That means a network like the Congestion Free Network as well dedicated walking and cycling options like Skypath combined with safe routes on road across the region. Those alternative networks won’t mean that everyone is going to suddenly use them or that people driving won’t suffer from congestion at times but it does mean that people can have a realistic option to make trips around the region knowing they won’t have the risk of suffering from congestion. As yesterday’s experience also shows, the key is also they are isolated from the rest of the road network. Because there is no dedicated route for buses over the harbour bridge all North Shore services were equally caught up in the chaos disrupting them too.
Note: we’ll be creating a new version to incorporate the change to the CRL with Mt Eden soon.
A true multi-modal transport system is also a resilient one so let’s get on and build those missing modes.
How do you define “optimal conditions” in a transport sense? The graphic below paints a stark difference in opinion on what constitutes “optimal conditions” for different professions:
Image from Patrick Kennedy, D Magazine, http://streetsmart.dmagazine.com/2014/11/07/age-of-enlightenment/
Now I’m both an engineer and an economist, so feel I have some insight into the motivation for whoever developed this graphic.
It highlights a very important issue: Engineers tend to measure performance using indicators that measure mobility, whereas economists tend to measure performance using indicators that measure value.
Now don’t get me wrong: I strongly believe that mobility has a value. I write this having just fanged up and down the northern motorway taking some visiting Australian guests to Tawharanui. But it’s not the only thing I value. Indeed, tonight I will take them to Fort Street for dinner at Ima’s.
I accept that what constitutes “optimal conditions” will change depending on the context, and that in some contexts mobility has a very high value. What I can’t fathom is why the transport/traffic profession have developed such simple and inflexible performance indicators to guide their work.
I’m going to say this right now: Level of service tells you *nothing* about what people value. Why? Because it’s measured independently of the costs associated with being able to move freely. We could, for example, enjoy great LOS if we bulldozed the entire city and replaced it all with twenty-lane motorways connecting to vast carparks, with the occasional office building or house dotted amongst the seas of asphalt. But I think it’s obvious that would be a really, really bad outcome for almost everything else that we value.
From an economic perspective, congestion in cities can be seen as a good thing. It’s an indicator that lots of people are using the city in lots of different ways – going to work, travelling to see friends or family, going shopping, visiting sports games or art museums etc. Congestion has costs, of course, but eliminating it entirely would be even more costly.
Wired magazine recently published a good, succinct explanation of induced traffic. It’s worth reading in full as it hits upon an incredibly important, often overlooked fact: it’s not possible to eliminate congestion by building more roads. Here are a few of the more interesting excerpts:
The concept is called induced demand, which is economist-speak for when increasing the supply of something (like roads) makes people want that thing even more. Though some traffic engineers made note of this phenomenon at least as early as the 1960s, it is only in recent years that social scientists have collected enough data to show how this happens pretty much every time we build new roads. These findings imply that the ways we traditionally go about trying to mitigate jams are essentially fruitless, and that we’d all be spending a lot less time in traffic if we could just be a little more rational.
But before we get to the solutions, we have to take a closer look at the problem. 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.
Los Angeles: Sitting in traffic after ignoring supply and demand for over 50 years.
In their excellent paper on the topic, Duranton and Turner describe this as “the fundamental law of road congestion: New roads will create new drivers, resulting in the intensity of traffic staying the same.” Their research also digs into a couple of other related and equally interesting phenomena:
- Better public transport provision doesn’t actually reduce road congestion – but it does enable more people to move without being affected by congestion
- Reducing road capacity has no measurable impact on congestion – if less road space is available, people take public transport or active modes instead, or avoid making low-value trips.
Urbanist.co also has some further discussion of Duranton and Turner’s work. The economists go on to suggest economists’ favourite answer to congestion: road pricing. (If you’re interested in reading more about that topic, Stu Donovan and I have written several posts about the economics of road pricing.)
So what can be done about all this? How could we actually reduce traffic congestion? Turner explained that the way we use roads right now is a bit like the Soviet Union’s method of distributing bread. Under the communist government, goods were given equally to all, with a central authority setting the price for each commodity. Because that price was often far less than what people were willing to pay for that good, comrades would rush to purchase it, forming lines around the block.
The U.S. government is also in the business of providing people with a good they really want: roads. And just like the old Soviets, Uncle Sam is giving this commodity away for next to nothing. Is the solution then to privatize all roads? Not unless you’re living in some libertarian fantasyland. What Turner and Duranton (and many others who’d like to see more rational transportation policy) actually advocate is known as congestion pricing.
Incidentally, I like Turner’s “Soviet Union” metaphor a lot – I’ve said on occasion that we’re running our transport system like a Polish shipyard.
Lastly, it’s incredibly important to consider induced traffic when making policy recommendations. As I wrote in my review of Alain Bertaud’s talks in Auckland, keeping commute times down is an important part of maintaining an efficient urban labour market. Some people seem to have taken Bertaud’s recommendation that policymakers focus on keeping average car commutes under 30 minutes (and PT commutes under 45 minutes) as a call for more roads. This is a superficially appealing but deeply wrongheaded idea.
Induced traffic means that building roads to keep commute times down will not work. And it will be expensive. While there is often a good case for specific road improvements to remove key bottlenecks or improve safety – the Victoria Park Tunnel comes to mind – Duranton and Turner’s work shows that a strategy of building lots of roads will not succeed in minimising commute times. An alternative approach is needed.
A lot of people think that Auckland’s got bad traffic congestion. The annual TomTom Traffic Index reinforces this perception – it regularly describes Auckland as one of the most congested cities in the region. (We’ve previously highlighted the methodological flaws with TomTom’s numbers – don’t take them at face value!)
However, I don’t think this perception matches up with reality. My experience is that Auckland has much better congestion than cities overseas. It’s incredibly easy to drive in Auckland. I’ve noticed that:
- Although speeds on motorways and arterial roads drop during rush hour, traffic keeps flowing at a relatively constant rate. It seems uncommon to get totally deadlocked traffic in Auckland – unlike in California, where it’s common to see speeds of under 20km/hr on freeways.
- The rush hour is incredibly short in Auckland – when I have to drive up to the North Shore after work to visit family, I find that traffic’s basically free-flowing after around 6:30. In other cities serious congestion starts much earlier and ends much later.
- Counter-peak traffic is shockingly low – on the occasions when I have to drive to Takapuna in the morning, I’ve found that I encounter few queues and no congestion on Pitt St, Victoria Park Tunnel, and the bridge.
Of course, Auckland is more congested than small New Zealand cities with one-tenth its population. That’s only to be expected. But is Auckland really more congested than other large cities overseas?
Jarrett Walker points us toward some new data that can help shed some light on this issue. A recent study (pdf) of commute times in Brazilian cities provides comparative estimates of average commute travel times for thirty large cities all around the world. I used data from New Zealand’s Household Travel Survey to add Auckland to the list. Here are the results:
As you can see, Aucklanders enjoy some of the fastest commutes of any city on the list. We travel faster than people in London, Stockholm, Sydney, Los Angeles, and Vancouver. Only Barcelona, a compact city with a densely-developed subway system, offers faster trips to work. (However, it would be good to see a few more Australian cities, like Perth and Brisbane, on the list for comparison.)
While population growth will put some pressure on Auckland’s transport infrastructure, this data suggests that our congestion problems are not severe at all. We look pretty good on Alain Bertaud’s preferred measure of transport accessibility! It seems like the impending completion of Auckland’s motorway network and the significant fall in vehicle kilometres travelled per capita over the last decade has given us a lot of breathing room on congestion.
Rather than trying to solve problems that can’t be observed in the data, we should use this breathing room to invest in real transport choices for Aucklanders. That means getting ambitious about building Auckland’s “missing modes”:
- A rapid transit network that reaches all parts of the city – starting with the City Rail Link and continuing with something like the Congestion Free Network
- A frequent bus network that is useful for more Aucklanders, more often – which Auckland Transport is currently doing
- Safe cycle infrastructure throughout the city – while Auckland Transport and NZTA are starting to deliver great projects like the Grafton Gully and Beach Road cycleways, there are still many holes in the network
- Good pedestrian-oriented streets – Auckland Council’s shared spaces in the city centre are fantastic but change hasn’t been as rapid in other parts of the city.
What’s your perception of Auckland’s transport problems?
It almost goes without saying that congestion is a terrible thing, so bad that it justifies the spending of massive amounts of public money as well as the impact on our cities from widening and building new transport infrastructure to rid ourselves – or at least reduce the level of – this terrible thing that is congestion. So you would expect cities with lots of congestion to be horrible places that are struggling to attract population and have a poor quality of life – while you might expect cities with less congestion to be great places that are attracting heaps of people and have a great quality of life. Right?
Well the reality appears to be quite different, as touched upon in this recent Planetizen article – which compares cities in the USA with some of the highest levels of congestion with those that have some of the lowest. Let’s start with the more congested cities.
Wendell Cox just wrote an essay trying to correlate density and congestion, asserting that density means congestion and congestion is really, really bad (or in his words, “less traffic congestion benefits a metropolitan area’s competitiveness.”)
So logically, the high-congestion cities should be declining, and the low-congestion places should be attracting Americans at a rapid rate. Right? Wrong.
In fact, the lowest-congestion cities tend to be a very mixed bag, while the high-congestion cities are doing relatively well. Cox lists ten high-congestion regions: Los Angeles, Houston, Austin, San Francisco, New York, Seattle, San Jose, Washington, Boston, and Portland. In all ten, the central city of the relevant region gained population between 2000 and 2010. These cities tend to be larger, relatively wealthy, high-cost cities, cities where keeping housing affordable is a bigger problem than demolition of worthless vacant lots.
And in all but two of these ten regions (all excepting Boston and Washington) the central city is more populous than in 1970. In these regions, there’s enough growth for city and suburb alike. Although some of these regions experienced regional population growth of 0-10 percent, not one of them shrunk, and two (Houston and Austin) grew by over 20 percent.
Reeling off cities like Houston, New York, Seattle, Washington, San Francisco and others hardly appears to be a list of US cities which are doing particularly badly at the moment. Even though they are apparently the most congested cities. Now let’s look at the least congested cities:
By contrast, Cox lists ten low-congestion regions: Indianapolis, Oklahoma City, Salt Lake City, St. Louis, Richmond, Kansas City, Memphis, Buffalo, Rochester, and Cleveland. A few of these (most notably Indianapolis, Oklahoma City and Salt Lake City) are doing reasonably well. But five of the central cities in Cox’s “hero metros” lost population in the 2000s (Buffalo, Rochester, Cleveland, St. Louis, and Memphis) and two more gained population in the 2000s but are still less populous than in 1970 (Richmond and Kansas City). In fact, Buffalo and Cleveland even managed to lose population regionwide, and not one of Cox’s high performers grew by more than 16.7% (metro Salt Lake City’s growth rate).
In addition, these low-congestion cities tend to be far more dangerous than high-congestion cities. Their average murder rate in 2012 was 19.5 per 100,000 residents, while the high-congestion cities’ murder rate was only 7 per 100,000—not surprising given the decline discussed above. Only one of the low congestion cities (Salt Lake City) had a murder rate as low as the average for the ten high-congestion cities.
Residents of Cox’s ten low-congestion cities have more reason to worry about dangerous drivers as well as dangerous criminals. I was able to find data for auto-related fatalities for sixteen of the twenty cities in Cox’s two “top ten” lists; the high-congestion cities averaged 4.7 traffic deaths per 100,000 residents in 2011, while the low-congestion cities averaged 9.8. To put the matter another way, the most dangerous of the high-congestion cities (Houston) had 9.1 traffic deaths per 100,000 people, while five of nine low-congestion cities had more traffic deaths per capita than Houston. The second most dangerous high-congestion city (Austin, clocking in at 6.4 deaths per 100,000) had a lower fatality rate than all but one of the low-congestion cities. The least dangerous of the low-congestion cities, Rochester, New York had a higher traffic death rate than five of the seven high-congestion cities.
St Louis, Buffalo, Cleveland etc. at first glance appear to be some of the US cities that have most struggled over the past few decades – losing a heap of population as US manufacturing moved off-shore. The very low congestion levels enjoyed by these places doesn’t seem to have any effect on their relative attractiveness – and seems to be linked with higher murder rates and much greater risk of traffic related deaths.
Michael Lewyn, the article’s author, suggests a possible reason for the connection between low congestion cities and these fairly poor statistics:
Or it could be that policies designed to limit congestion (like widening roads to support high speeds, chopping up downtowns with highways and turning them into giant parking craters) have actually had some positive effect for congestion, but at a heavy cost.
Given that generally we know congested cities are more economically productive, is it time we stopped stressing about this issue so much and focused on things that really matter like levels of accessibility and the extent to which people are able to get around unaffected by the particular road conditions of the moment. Of course that’s a key driver behind the the Congestion Free Network.