By Roger Bacon

This is the unabridged version of an article first published in The Canberra Times on Sunday 10 April 2022.

“Adding highway lanes to deal with traffic congestion is like loosening your belt to cure obesity.” – Lewis Mumford, American urban planner, 1955

“Just gave my name in Starbucks as ‘You’re not stuck in traffic.’ As the barista shouted out my ‘name’ repeatedly, the whole place responded ‘You ARE traffic,’ and I realized every single person out there now completely understands ‘The Law of Congestion.’ Try it.” – Brent Toderian, Canadian urban planner, 2018

St Paul had his moment on the road to Damascus. Mine hit me on the road to Pialligo, late last Christmas night, while driving to the Animal Hospital.

The revelation was about traffic congestion on Canberra’s constricted boulevards. At 1.30 am on Boxing Day, there isn’t any. Traffic, that is.

So when our local leaders go on about widening roads to ‘bust congestion’ and ‘get hard-working Canberrans home to their families [a few minutes] earlier’, they are not just offering up a prayer to Our Blessed Lady of Acceleration. They are talking about spending tens of millions of our money to solve a problem that only exists – if at all – for about four hours on working days.

That’s about 1,000 hours a year, or about 11 percent of the time. For the other 7,766 hours, there’s no problem. Mention Canberra congestion to someone from a big city, and they fall about laughing.

All the evidence is that if you choose to make something – like driving  – easier and more convenient, people do it more. This is what economists call ‘induced demand’. Road widening is a classic example. The increased road capacity quicky fills up again. The Katy Freeway in Houston, Texas – the world’s widest – is now up to 26 lanes, and still gets congested.

Traffic doesn’t behave like a liquid, moving faster through a wider and smoother pipe. It behaves like a gas, expanding to fill the available space.

‘Liquid’ vs ‘gas’ models for traffic

“… engineers are shifting their thinking toward traffic. Formerly, the model for traffic was a “liquid,” where adding capacity relieved congestion. Now engineers are starting to see traffic as a “gas,” where traffic volume expands to fill the capacity.

Researchers at the University of California Institute for Transportation Studies recently published the results of their study on capacity expansion projects in many California cities. They found that within one year, 60% of the new capacity was consumed with new, or longer, trips. Within five years, 90% of the capacity was consumed.

Evidence from capacity reductions verifies this thinking – removing capacity reduces traffic.

– from Peter Jacobsen, letter to the Los Angeles Times, 14 May 1997

Spending big money to make congestion worse is not very clever, even if it appeals to like-minded voters. It’s also completely incompatible with several other worthy aims, including better public health and minimising climate change.

It would be better to put that kind of money into things that actually will reduce road congestion, like public transport and cycling.

Sooner or later, we will also have to bring in road user charges in place of fuel excise. Electric vehicles make it inevitable. As with any number of goods such as electricity and air travel, there will be ‘peak’, ‘shoulder’ and ‘off-peak’ rates.

This video clip perfectly illustrates the folly of widening roads to ‘bust congestion’. It’s from a recent episode of the ABC series Utopia, and has gone viral in the urban planning community worldwide.

We need to start making better choices.

“When you design a city for cars it fails for all, including drivers. When you design a multimodal city it works for all, including drivers.” – Brent Toderian, 2015