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“The remarkable manner in which new roads create new traffic”: a history of induced demand

Sir Charles Bressey

Sir Charles Bressey, 1937: “remarkable manner in which new roads create new traffic.”

Transport academics tend to credit the discovery of ‘induced demand in transport’ to J.J. Leeming, a British road-traffic engineer and county surveyor, writing in 1969. He observed that the more roads are built, the more traffic there is to fill these roads. The idea was conceived shortly after German mathematician Dietrich Braess released the Braess’s paradox which shows that “selfish” motorists can’t be relied upon to consider the optimal travel times for all rather than just themselves, leading to delays for all. These ideas were further expanded in the Lewis–Mogridge Position of 1990 and the Downs–Thomson paradox of 1992.

The idea that building more roads leads to more congestion was used by anti-roads campaigners from the 1970s on to combat the futility of road building, and it became an orthodox position – briefly – following advice to Government from the Standing Advisory Committee on Trunk Road Assessment study of 1994. Margaret Thatcher’s road building programme – “the biggest since the Romans” – was halted. (Despite “austerity” it’s back again.)

Campaigners have a pithy phrase to describe induced demand:

“Building more roads to prevent congestion is like a fat man loosening his belt to prevent obesity.”*

Neat, but not neat enough to prevent today’s road building programme. New roads are being built and these new roads will quickly fill with traffic, leading to calls for yet more roads to be built. And so it goes on.

But induced demand was known about long before 1969. Writing in 1866, surveyor and engineer William J. Haywood, one of the builders of the Holborn Viaduct, said the new thoroughfare would attract more travellers: the “facility of locomotion stimulates traffic of itself”. His solution? Build more and more roads, of course. This was also the conclusion of Sir Charles Bressey’s Highway Development Survey for London, published in 1937. In his report – penned with the great architect, Sir Edward Lutyens – Bressey wrote:

“As a typical instance may be quoted the new Great West Road which parallels and relieves the old Brentford High Street route. According to the Ministry’s traffic census extracts…the new route as soon as it was opened carried four and a half times more vehicles than the old route was carrying. No diminution, however, occurred in the flow of traffic along the old route and from that day to this the number of vehicles on both routes has steadily increased…These figures serve to exemplify the remarkable manner in which new roads create new traffic.”

Bressey’s solution? Same as Haywood’s. More roads.

In an article about the Bressey Report in the Illustrated London News in 1938, an illustrator imagined what London would look like if Bressey and Lutyens had their way, including this not altogether desirable plan for a car park on Trafalgar Square:


The clipped, patriarchal tones of Bressey’s voice, and his stiff bearing, can be enjoyed in the period film below. It was shot in 1939 for the Post Office, hence the middle portion featuring the GPO’s incredible private underground network in London. Bressey is shown in his office, complaining that Sir Christopher Wren was constrained by the forces of “conservatism” for not being allowed to carry out his plan of giving London a series of wide boulevards following the Great Fire of 1666.

Sir Christopher Wren's post-1666 map of London. Despite claims from Wren and his son, the plan was never seriously considered. For a start it was topographically impossible. Click for huge version.

1744 copy of Sir Christopher Wren’s post-1666 map of London. Despite claims from Wren, and his son, the plan was never seriously considered. For a start it was topographically impossible. Click for huge version.

Wren griped:

“Its ‘Practicability… without Loss to any Man, or Infringement of any Property, was…demonstrated, and all material Objections fully weigh’d and answered. Yet nothing was effected because of ‘the obstinate Adverseness of a great Part of the Citizens to alter their old Properties, and to recede from building their houses again on their old Ground and Foundations; as also the distrust in many, and Unwillingness to give up their Properties, tho’ for a Time only, in to the Hands of publick Trustees, or Commissioner, til they might be dispens’d to them again, with more Advantage to themselves, than otherwise was possible to be effected…”


In the film, when Bressey complains about London’s “narrow, medieval streets” the camera pans over a succession of very wide London streets, rather negating the voiceover. [The chipper, modern-sounding voiceover is of Herbert Hodge, the London cabbie who helped popularise ‘estuary English’].

And here are some more choice quotes from magazines, authors and politicians regarding what they felt were pressing transport matters.

“The majority of the public today relies for transport of every kind mainly on the roads, and everything goes to show that they are doing so to an unprecedented degree… People travel now more than they have ever travelled, and in the future they will travel still more. If they want more roads to travel by, you may be sure that they will get them, for in the last analysis nothing can stop the development of the road.”
R.M.C. Anderson, The Roads of England, 1932

“A motorist is apt to complain of the ‘overcrowded’ condition of the road if he finds he has not continually got a whole mile-long stretch of it to himself, but is one of a widely spaced and rapidly moving queue of half a dozen or so. He will declare there is no pleasure in motoring under such conditions. He will search his map for some alternative route by quiet lanes where he can speed along with the road to himself. And when others find that alternative route and all further alternatives are exhausted, he proceeds to demand a new road system so that his motoring may again become a pleasure.”
Thomas Sharp, Town and Countryside, 1932

“The bicycle’s popularity complicates traffic control throughout Europe.”
The Rotarian, Chicago, August 1936

“I think in the past we have followed in vain the futile policy of trying to make traffic fit the roads, and we cannot hope to see things better until we make up our minds to fit the roads for the traffic. Increase in road traffic is an enemy which grows more formidable every day. I would suggest that it is dangerous to delay matters further, and I do hope the Minister of Transport will consider acting on the Bressey Report as soon as is reasonably possible.”
Lord Teynam, June 1938



* This phrase is based on a 1955 article by Lewis Mumford. Writing in The New Yorker, the great urban planning specialist suggested that “people … find it hard to believe that the cure for congestion is not more facilities for congestion.”

Most of the fancy cures that the experts have offered for New York’s congestion are based on the innocent notion that the problem can be solved by increasing the capacity of the existing traffic routes, multiplying the number of ways of getting in and out of town, or providing more parking space for cars that should not have been lured into the city in the first place. Like the tailor’s remedy for obesity – letting out the seams of the trousers and loosening the belt – this does nothing to curb the greedy appetite that [has] caused the fat to accumulate …



10 thoughts on ““The remarkable manner in which new roads create new traffic”: a history of induced demand

  1. American Cyclist / Reply February 2, 2013 at 2:27 am


    Is it possible that, whatever the transportation mode, the result might have been the same? Consider: If the automobile had never been invented and we were still riding horses, wouldn’t these scholars have complained about all the space dedicated to bridle paths? If all we had was trains, would they complain about demand for tracks?

    And, consider the alternative. If we didn’t have cars, trucks and roads and still relied on bicycles and wagons, how would we be shipping goods and people from city to city? Wouldn’t we all be limited to fairly small circles of commerce and social interaction?

    I’m just wondering what life would be like in a world without cars…even though I’m a passionate cyclist and have been one for over 40 years. However, I’d rather live in a world where I have mobility and freedom to travel long distances and see far off places.

    Love your blog!

    • carltonreid / Reply February 2, 2013 at 10:00 am

      Cars are wonderful. And that’s the car’s downfall: everybody wants one. Cars work best when the roads are free of other cars. Increasing wealth and reduced prices meant car ownership went mainstream quickly. I’ve just added a 1950s video to the story. This shows chronic congestion on a Californian freeway. The US has more space than the UK but no matter how much asphalt you lay down for cars it’s never enough.
      Cars are just so darn comfortable. Now people plan for getting stuck in congestion, and factor in delays. That’s a crazy, unsustainable system. There was also plenty of congestion back in the days before cars but this was only in cities; now we have congestion away from the cities, too.
      We don’t need more roads we need intelligent use of the existing and rather quite copious network. There’s lots of roadspace at night – travel on a UK motorway at 3am and it’s almost empty – it’s how we use it in the daytime that’s the problem. When everybody wants to use the same road at the same time that’s when the blockages happen.
      Unrestrained use of large, heavy lumps of metal to transport solo travellers is incredibly inefficient, especially when it’s in huge numbers. Increased individual mobility – the dream car makers sell – is not possible everywhere. Average speeds in city centres are low: the average speed of a car in London today is about the same as a horse-pulled buggy in the 1890s.
      I’m not anti-car. I own one and I drive it. But not for short journeys. For short journeys I either walk or ride a bike. There’s no need to get rid of cars but there’s a pressing need to use them much more intelligently. And as the Braess paradox reveals, this cannot be left up to individuals. That is if we want a functioning road network and one that hasn’t asphalted every square inch of land. There would be no point having hyper-mobility but for the only place to go is from road to road.

      • John Dough / Reply February 3, 2013 at 12:38 pm

        I agree with most of what you say. I would point out that the reason for empty roads at night vs. busy roads at day is human patterns. Water delivery systems are the same. If we used water at the same rate, day and night, we could have smaller pipes. But, we don’t and so we pay the difference. Same with electricity and churches. We must allow for peaks and accept underutilization at other times.

        A professor once told me, “You don’t design a church for Easter Sunday.” Later, I concluded, you don’t design it for an average occupancy either because most of the time, its empty. So, it’s a balance.

        So, there we are. We have roads that have to accommodate “peak” (or reasonably close to peak) travel flows, or we have too frequent gridlock, which most would find unacceptable and we have to accept the we have excess capacity at other times, which most do not find unacceptable.

        • carltonreid / Reply February 3, 2013 at 6:08 pm

          Totally! Which is why we have to change those human patterns before slapping down loads more infrastructure. Sweat the assets, I believe some call it.

          • John Dough / February 4, 2013 at 4:47 am

            I’ll have to know how you plan to do that before I can agree.

            Some places in America vary water rates by time of day…higher at peak use times. Similarly, and more common I think, is electric companies that do the same. It’s called congestion pricing. It makes you think, do I really have to water my lawn when everybody else is taking a shower or can I do it at midnight, when everybody’s in bed? That leaves me with the decision and I like that.

            But, if the pastor on the church says, look, I’m going to assign you each a day of the week and you must worship only on that date, then that’s an approach I wouldn’t care for. That approach makes me bristle and I’m suddenly looking for another church…or another pastor!

            So, what exactly do you mean when you say “we have to change those human patterns”? More important: Who’s “we”?

      • Ride2Wk / Reply October 26, 2013 at 12:09 am

        Totally agree. Like Carlton, I like using cars but only for “necessary” trips such as longer distances, carting stuff or taking the whole family when the bike is not so suitable. I ride to work every day and use the bike for most trips up to about 30 km. (20 miles). The problem with cars is that they are too easy & too many people only care about themselves. I hate to sound like a socialist but most people never think of us as a society & what’s best for all of us if we actually worked together & modified our behaviour. If most people used bikes, walked or used public transport as much as they could, the roads wouldn’t be so congested and we would all be better off in so many ways. Our whole system of living has been build over time by working together to overcome problems & achieve greater things than just what 1 person can do.
        We need to start thinking of traffic congestion as a problem like a war. Hilter’s Germany would never have been defeated if most of the English & allied people hadn’t all worked hard together & sacrificed in many ways for the common good that we now take for granted. Things like congestion charging are a good step in the right direction. Changing urban form, better bikeways & public transport are others.
        One that England, Australia & other Anglo-Saxon nations seems to need most is a change of attitudes & laws to stop accepting harassment & “accidental” killing of cyclists & pedestrians as just minor issues. The Dutch system seems to work better from what I’ve heard.
        Recently in Australia a suspended young driver with a very poor driver infringement record was sentenced to only 4 months jail for killing a young cyclist while failing to pay attention to the road. While jailing him for a long time is expensive and probably wouldn’t achieve much individually, personally I think he should be sentenced to 10 years hard labour on public works projects to pay back his debt to society. That sort of consequence might scare other drivers into paying attention and not taking so many risks with everyone else’s lives.

    • Simon / Reply February 3, 2013 at 1:13 am

      The situation is different for other transport modes because other transport modes require less space per person. It’s only cars that require massive amounts of space in order for people to travel.

      • John Dough / Reply February 3, 2013 at 12:25 pm

        So, now, here we are, and it’s 2013 and we have all this inefficient infrastructure out there, taking up massive amounts of space per person (in some places but, you might agree, not all). What are optional solutions?

        We could, if we were omnipotent, demand drivers double up occupancy…carpooling.

        If we were endlessly wealthy, we could replace congested roads with a mandatory other system (trains? buses? shuttle cars?) and leave uncontested roads alone.

        We could employ congestion pricing.

        I would, though, modify your statement. It’s not “cars” that require massive amounts of space per person, it’s “single occupant cars” that require massive amounts of space per person. If you could overnight increase average occupancy from, say, one to, say, four, you could reduce vehicle volumes by 75% and/or increase person capacity by 300%.

        • carltonreid / Reply February 3, 2013 at 6:07 pm

          I agree there. When cars have multiple occupants their efficiency increases many times. Use of large cars to transport one human is not efficient use of space or resources. Really, most people who need to be motorised ought to be on scooters, they’re more space efficient. Or those motorbikes with roof-like structures.

      • carltonreid / Reply February 3, 2013 at 6:03 pm

        And not just roads, but acres and acres of car parks (where shops etc are mandated to allow so much space per customer, most of it wasted, designed as it is for rush times); and other infrastructure for cars.

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