An article in Toronto’s Globe and Mail newspaper just over a week ago, using the rather provocative title of “Sick of Congestion: build roads not transit” has unsurprisingly led to a lot of fisking of the information contained in the article – particularly around the different ways of defining congestion and how easily they can be misused. A good example of a response is this from Jarrett Walker.
Essentially, the argument put forward in the article is that when we look at cities around the USA (and internationally), at first glance the data appears to be showing that cities which have built a lot of freeways in the past few decades have lower levels of congestion than those which haven’t. Here are the key paragraphs:
This connection between road construction and congestion has been most comprehensively studied in the United States. There, 30 years ago, the Texas Transportation Institute at the Texas A&M University created an annual Travel Time Index (TTI) that estimates how much time traffic congestion adds to commuting by comparing actual travel times of commuters in different cities with the time it would take to travel the same distances in the absence of congestion.
Over the decades of its existence, the TTI has revealed some fascinating shifts. In the early days of the index, Phoenix, for example, had the 10th worse congestion among major urban areas in the U.S., despite being only 35th in population. It has more than doubled in size in the ensuing decades (it is now the 12th largest urban area in the U.S.), but its traffic congestion has fallen to 37th.
What explains this major improvement? A huge expansion of public transit? Hardly. Try a major road-building program. Something similar happened in Houston.
At the other end of the spectrum, Portland, Ore., has pursued road-skeptical policies similar to many major Canadian cities. The result is markedly worsened commuting times. According to the TTI, over the past 30 years Portland has gone from having the 47th worst congestion in the U.S. to the sixth worst.
Something in the next paragraph jumped out at me when first reading it – when mention was made of New Zealand cities as examples of those that had high congestion and hadn’t built many urban freeways.
Now data are starting to emerge that allow us to compare commute times among similar rich-world industrialized countries in Western Europe, the U.S., Canada, Australia and New Zealand. The results are not encouraging for the anti-car crowd. The worst urban congestion in this group of countries is in New Zealand, followed by Australia, countries that have invested relatively little in urban freeways.
If Auckland, with our gigantic spaghetti junction and motorways to just about every corner of the city, is an example of us not having invested much in ‘urban freeways’, I’d hate to see a place with lot of them – although Toronto’s Highway 405 (below) is pretty bad. I actually had a quick look at some figures from US cities with populations greater than 1 million people and from what I can tell based on some admittedly very rough calculations is that the size of motorway network would probably put us within top 10 US cities. Might have to look into that in more detail for a future post.
But the strange mention of New Zealand aside, the real issue with the article is its reliance upon congestion information from the Texas Transportation Institute that is decidedly dodgy in how it’s applied. Let’s pick up on Jarrett Walker’s criticism of the source data:
TTI believes that traffic congestion is a valid measure of people’s ability to access the resources of their city. They do not measure actual travel times for all people, or the liberty and economic liberty that a good urban transporation system offers. They apply these things as factors to a degree, but their bottom line is road congestion.
Specifically, their metric is the difference in travel times, by car, between travel time on congested roads and the same roads in a free-flow condition. In other words, their baseline utopian condition is abundant free-flowing roads at all times of day. (That condition is actually an economic impossibility in a city above a certain size with a healthy economy and no road pricing.)
Once you insist on measuring congestion, and against that fantasy baseline, you can get absolutely everything backwards…
… If you count everybody’s commuting time, Portland is ahead of most US metros. … it is only congestion that is worse. Yes, like all dense cities, Portland has exactly as much congestion as it makes room for, but it has low overall commute times, mostly because its carefully mixed density allows many people to commute very short distances. Remember, if you are measuring car congestion, Portland’s transit riders and cyclists and the many people who can walk to work simply do not exist. Crowley disses “congested” Vancouver for the same reason, even though Vancouver is the only Canadian metro where the long-term trend is toward shorter commute times, due to continued consolidation of housing and business around transit.
Jarrett sort of dances around the key point here while hinting at it in a number of ways. This key point is that for many people in the Portlands or Vancouvers of this world the level of basic congestion is irrelevant because they’re not affected by it. They’re walking, cycling, on a bus (as long as it’s in a bus lane or on a busway), a tram, a train or whatever. They’re not in the congestion.
This is the key point of the Congestion Free Network: it provides people with the ability to ‘opt out’ of congestion. This approach highlights that there are two elements to congestion:
- How bad is the congestion? (Congestion intensity)
- What proportion of people experience the congestion? (Congestion exposure)
It is the combination of these two elements which is what really matters – the actual effect of congestion can be increased or decreased not only through its intensity (which is all that the TTI measure, and arguably not that well either) but also through changing the proportion of people experiencing congestion. It seems that transport planners and particularly transport engineers focus so much on trying to reduce the intensity of congestion, even though this is nearly impossible due to induced demand, whereas the long-lasting way of reducing congestion is to provide ways to remove people from the congestion.
This means that a focus on cycleways, bus lanes, rapid transit and freight lanes (because it can be very important to shift goods around in a way that’s unaffected by congestion) are the true ways of reducing the actual effect of congestion. They’re also the only long-lasting ways of doing so. Todd Litman focuses on this distinction in his recent piece on Planetizen:
…the Texas Transportation Institute’s Travel Time Index, the INRIX Traffic Scorecard, and TomTom’s Traffic Index only measure congestion intensity, the degree that traffic declines during peak periods. Such indicators do not account for exposure, the amount that people must drive during peak periods and therefore their total congestion costs. Intensity indices are useful for short-term decisions, such as how best to cross town during rush hour, but are unsuited to strategic planning decisions that affect the quality of transport options or land use development patterns, and therefore the amount that people must drive. For planning purposes, the correct indicator is per capita congestion costs.
For example, a compact, transit-oriented city may have a 1.3 Travel Time Index (traffic speeds decline 30% during peak periods), 60% automobile commute mode share, and 6-mile average trip lengths, resulting in 34 average annual hours of delay per commuter; while a sprawled, automobile-dependent city has a 1.2 Travel Time Index, 90% automobile mode share, and 10-mile average trip lengths, resulting in a much higher 45 average annual hours of delay. Intensity indicators imply that the compact city has worse congestion due to greater peak period speed reductions, although its residents experience lower total congestion costs because they drive less during peak periods.
I talked about TomTom’s Traffic index here.
As part of the next phase of promoting the Congestion Free Network, we are going to focus strongly on expanding this new approach to defining congestion – so that it can actually be a useful measure of transport success, rather than something that suggests we do stupid things like building more (or bigger) urban motorways.