Image by jodeng from Pixabay
Traffic jams: we all hate them. From regular rush hour tailbacks to Bank Holiday horror shows, how many hours do we waste in nose-to-tail queues, bored out of our skulls, half-hoping for a zombie apocalypse to clear the streets?
If only there was another road to ease the pressure. If only the government would get off its backside and do something!
New roads seem such an obvious, straightforward solution. If you have 100,000 cars trying to use the same road, then two roads will mean 50,000 on each, and we can all get home in time for tea.
Well, yeah… except that building extra roads hardly ever eases congestion.
Occasionally, they can relieve traffic through town centres built in the middle ages, but even then, it’s less than you’d think.
To understand why, we need to dive into the crazy world of generated traffic.
To drive, or not to drive?
To explain generated traffic, aka induced demand, let’s take an example.
Imagine you live outside a medium-sized city, and you’d love to drive into that funky area to check out restaurants and shopping. The problem is that the one road into town is clogged with traffic. It’s going to take you an hour to get there and an hour back. So instead, you save that trip for a special occasion and usually shop and eat more locally.
But then, a new road is opened. Now, you can drive a blissfully uncrowded route into town in just ten minutes. Suddenly, that trip looks more attractive, and you’re heading into the bright lights at every opportunity.
And as those new benefits don’t just apply to you, guess what happens next? Yep, everybody gets the same idea. Before long, the new road is just as busy as the old road. The new road has generated its own traffic.
Not just a theory
So that’s the theory of induced demand/generated traffic. What about in practice? An excellent article in Vox and a more detailed one from the Victoria Transport Policy Institute (VTPI) in Australia provide some real world examples:
- In May 2014, after five years of work and $1 billion, the widening of the Los Angeles’ I-405 freeway was completed. The result was that traffic moved just as slowly as before the road expansion (Vox article).
- When new bridges were built in Istanbul in 1973 and 1988, traffic congestion soon returned to previous levels (VTPI, p 9)
- A 2019 study in Norway concluded: “highway expansions provide only short-term congestion relief, and by increasing sprawled development, increase total traffic growth.” (VTPI, p 7)
- A 2020 study of 545 European cities found that “urban highway expansion tends to increase vehicle traffic and so fails to solve congestion”. In addition, “each 1% increase in highway lane-kilometres typically increases total vehicle kilometres by 1.2%.”
We could go on, but you get the point. All over the world. it’s the same story: more roads or more lanes just means more traffic. However, one last study from the VTPI is worth quoting in its entirety, because it shows what a monumental failure adding extra roads can be:
The report, The Congestion Con: How More Lanes and More Money Equals More Traffic (TfA 2020) analyzed how roadway expansions affected per capita congestion delay in the 100 largest urbanized areas in the U.S. between 1993 and 2017. During that period governments spent more than $500 billion on highway projects but congestion grew 144%, far more than population, and the regions that expanded roads the most tended to have more congestion growth than those that expanded less. The authors concluded that this resulted from generated traffic which filled the added capacity. plus the long-term effects of increased sprawl and increased per capita vehicle travel induced by the additional roadway capacity.
[We added the bolding]
So, why do we keep adding road capacity?
Just to be clear, there are circumstances where extra road capacity can reduce congestion. Obvious examples are traffic bottlenecks, where two lanes merge into one, or bypasses for mediaeval towns that weren’t designed for modern cars. But as a general rule, we’ve seen that adding roads just doesn’t work that well.
And that raises a huge question. If adding capacity doesn’t solve the problem, why do we keep doing it?
The Vox article has a simple, though jaw-dropping, answer: planners just assumed it would work. Until recently, there wasn’t that much empirical testing of what adding roads actually achieved. Perhaps it’s because adding road capacity seems so intuitive that very few questioned the logic of it.
On top of that, we’ll add our own speculation. Let’s say you’re a politician and your voters want you to do something about the terrible congestion problems. Your options are:
- introducing road tolls
- improving public transport
- building a new road
The first option is always horribly unpopular and feels like a punishment for your long-suffering public. The second one… maybe, but people love their cars, far more than going on the bus. The third one offers a common-sense solution that everyone understands – and it offers a tantalising vision of zooming down a brand new, lightly trafficked road. It feels like a gift to the people.
And you do want to be re-elected, don’t you?
OK brainbox, what does reduce congestion?
Ah, that’s for next time… see you in two weeks!
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