We must no longer justify new highways on the basis of reduced congestion

Ring road, more lanes on Deerfoot will not improve traffic

Note: After some clarifying discussion with Councillor Keating on Twitter, I’ve amended the end of the article to better reflect his point of view.
There’s a widely studied and documented economic principle known as induced demand. It stands on a very simple principle: If something becomes cheaper or easier to use, more people are likely to use it.

This is a very basic but extremely powerful principle. What this means is that if more of something (like highway lanes, for example) becomes available, this increase in supply causes a decrease in price. If you build more lanes and make a highway cheaper and easier to use, more people will use it. When I say “cheaper”, I generally mean less time spent in heavy traffic, and therefore less time spent driving in total. The end result is that if you try to relieve congestion by building more highways, you will get more congestion from the increase in people using them, until you’re right back where you started. This has been found time and time again, including in a study of a large area of the US:

In 2004, a study of the entire Mid-Atlantic region found “changes in lane-miles precede changes in travel” and a meta-analysis of dozens of studies found that, on average, a 10 percent increase in lane miles induces an immediate 4 percent increase in vehicle miles traveled, which climbs to 10 percent — the entire new capacity — in a few years.

The last line is so important it’s worth restating: all of the extra capacity built was used up again in a few years. This is from new cars, making new trips.

In Europe, they have taken this phenomenon to heart. In Great Britain, for example, new highways can no longer be justified solely on the basis of reduced congestion, and this policy exists across many other European countries. This leads me to ask: if after spending all this money on new urban highways, the road will be just as congested as before, why are we doing it?

One common argument for increased capacity despite accounting for induced demand is that even with the same congestion as before, more people are moving around in total, which is a net benefit to society. That is a shaky argument that really depends on how you measure “net benefit”. Often neglected is the fact that driving is worse for the environment and likely worse for your health, so the benefit from making a trip by car you would have not made at all (or made using some other method of transportation) would have to be pretty substantial.

Quite simply, billing new and wider highways as reducing congestion does not make sense. It is not a solution to the stated problem in any way, shape, or form.

There’s an alternative, though, and it’s (surprise surprise) public transit. Public transit has the ability to allow people to make more trips with much less expensive and space-hogging infrastructure investments. Public transit scales unlike any highway possibly could, and, unlike highways, transit actually improves with induced demand. When a transit service is improved (for example by increasing frequency or building a dedicated roadway to bypass vehicle traffic) more people will use it, and this in turn justifies better service in the area, leading to more people using it.

Here’s the kicker: Even with better transit, the roads will likely stay just as congested as before. This is sometimes used as “evidence” of transit not helping improve congestion at all. This happens because as people move from cars to buses, more road space is freed up, which in turn gets used again because of our now old friend induced demand. The key is that the impact of ramping up transit capacity is much lower than ramping up road capacity. Professional transit consultant Jarrett Walker explains the idea well:

Transit raises the level of economic activity and prosperity at a fixed level of congestion. Congestion appears to reach equilibrium at a level that is maddeningly high but that can’t be called “total gridlock.”  At that level, people just stop trying to travel.  If your city is car-dependent, that limit becomes the cap on the economic activity — and thus the prosperity — of your city. To the extent that your city is dependent on transit, supported by walking and cycling, economic activity and prosperity can continue to grow while congestion remains constant.

Calgary’s ring road and the current studies on Deerfoot are perfect examples of increasing highway capacity in an effort to reduce congestion. The east portion of the ring road has been open for some time and Councillor Keating has done a wonderful job of explaining how it has not helped reduce congestion on Deerfoot at all. Unfortunately, he calls for more lanes instead of actually useful solutions. Though he does call for some widening at pinch points, he understands the need for thinking differently:

And who can blame him? It’s good to see decision makers speaking out against what’s been repeated time and time again across North American cities, and we need more of it. When it comes to urban highway congestion, we’ve been beating our head against a wall repeatedly and wondering why we always have a headache. It’s time to heed the less of induced demand and stop supporting highway lanes on the entirely misleading promise that traffic will get better.

Willem Klumpenhouwer

Willem is a PhD student in transportation planning and engineering at the University of Calgary, working on improving transit schedule design. In his spare time, Willem does programming projects and is a volunteer and improviser at the Loose Moose Theatre.

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