Gridlock, and confirmation bias

Way back in 2003, the north side of Trafalgar Square – the portion in front of the National Gallery – was pedestrianised, with the road running in front of the gallery, that severed it from the square, removed.

Before the scheme was even implemented, it was ‘feared’ that gridlock would result, and indeed gridlock in the area continues to be blamed on the closure of this small stretch of road, particularly by cab drivers.

But even before this section of square was pedestrianised, gridlock still occurred.

Trafalgar Square traffic jam, April 1976

Trafalgar Square

Photograph taken from here

Photograph taken from here

Trafalgar Square has always been clogged, even as far back as the 1940s.

Trafalgar Square

If this short stretch of road in front of the National Gallery were to be reopened to motor traffic, perhaps motor traffic in the area might flow more freely for a short period, but after a while the ‘extra’ road space would inevitably fill up again, returning the square to its previously clogged state.

This is the nature of demand for road space in central London; demand for driving in London outstrips the amount of road space available (or that ever could be available), so whatever amount of road space that is provided, large or small, will just get filled.

The problem is that drivers in London don’t see things this way; the congestion they are sitting in must have been ’caused’ by this or that closure; that subtle change to the way the roads are arranged; that extra bit of pavement that’s been created; or, pertinently, that new bit of cycle infrastructure.

This applies outside London too, of course. The inner ring road in Horsham has recently been subject to roadworks – minor changes to install a better pedestrian crossing – reducing its four or five lane width to just two lanes, in places.

Screen Shot 2015-09-18 at 12.21.59Inevitably, these temporary changes are alleged have ’caused’ gridlock.

Screen Shot 2015-09-18 at 12.26.40

This overlooks the fact that roads in the town are regularly congested, even in the absence of roadworks. Again, demand outstrips supply, so people driving on roads in Horsham have in a sense ‘adapted’ themselves to the available supply of road space. We are seeing the temporary effects of some reduction in that supply. I say ‘temporary’ for a couple of reasons.

Firstly, these roadworks are on a road that didn’t even exist until the mid-1990s. It was bulldozed through, demolishing buildings, to bypass an existing two-lane road, and to open up access to a new Sainsbury’s supermarket. So it’s entirely possible to argue that traffic capacity – even with the roadworks – is still greater than it was in 1995. The new, wider road, has just been filled up in much the same way as the old one was; the difference is that this new road is four lanes wide, rather than two lanes wide. The roadworks – which are visible from your car, as you sit, stationary, in congestion, appear to be the proximate cause of your delay, but in reality motor traffic congestion is inevitable in urban areas. The number of people who might want to drive outstrips the amount of space we can give them, or at least should be willing to give them, without destroying the fabric of our towns and cities.

Secondly, people are rational. They will not sit in congestion, day after day, month after month; they will adapt. (Or at least, many will – and that will be enough). They will choose a different time of day to make their journeys by car. They will choose a different route, by car. They may even choose a different mode of transport (heaven forbid). Indeed, to return to the example that opened this post, the reduction of space for motor traffic around Trafalgar Square did not, in fact, create extra congestion on the roads in the surrounding area.

Problematically, this kind of behaviour is not addressed by modelling of road- and junction-changes. For instance, the ‘delay’ forecasts produced by Transport for London for the new Superhighways – which generated alarming headlines – assumed that people’s behaviour was fixed. That they would not change their time of travel, their route, or even their mode of transport.

Short-term increases in congestion caused by lane closures due to roadworks, or permanent reallocation of road space, will inevitably smooth out over time as people adapt, even if at the time it is apparently ‘obvious’ that those changes have created a ‘gridlock’ that would exist anyway.

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17 Responses to Gridlock, and confirmation bias

  1. elvissawow says:

    Exactly the same is happening in Leeds at the moment. There are currently roadworks for a segregated cycle lane being built which has resulted in one lane of dual carriageway being closed temporarily. There’s been a predictably hysterical reaction from the local tabloid and even one councillor has been quoted as saying she wouldn’t have backed the scheme if she’s known it would ‘such disruption’.

  2. Kie says:

    The level of congestion is determined by peoples level of willingness to sit in traffic jams, it’s funny that TFL et al don’t understand that simple and obvious fact.

  3. ORiordan says:

    In the book “Urban transport without the hot air” by Steve Melia, he makes a compelling case (to me anyway…) that it is impossible to “solve” congestion in urban areas like London as there will always be more demands on the space than there is space available. Even if a driver switches from their car to another mode, there will always be another driver only too willing to take their place on the road.

    So rather than trying to solve something that can’t be solved, the approach should be to mitigate against congestion by allocating road space to public transport, walking and cycling. Drivers will still be stuck in gridlock, there will just be fewer drivers stuck in gridlock …

    • That Steve Melia book is most refreshing – just getting towards the end now.

      The deep irony about road space allocation is that the advocates of freedom to drive cars wherever they can are the ones who would most vehemently reject the economic ideology of those who they would look to for leadership. More simply put – the right wing would say “use the market”. This would let the owners of road space charge whatever they could get for access to it. Let central and local government “owners” charge feasible tolls on every inch. Keep increasing the price until revenue starts to go down, then start fragmenting the market to charge some a little extra – and so on. Better still, privatise the whole thing from the outset and let the emergent road cartel do the same things more energetically in the interest of their global shareholders and CEO reward structures.

      To put all that another way, traffic control/management is a highly political and should be understood as such. Bristol (as hinted at in Melia’s book) is a great case study of how local political jealousies can thwart intelligent action.

  4. michael says:

    I can’t help but Imagine if most inner city roads were now mostly full of people travelling on bikes. Who in their right mind would decide we should instead realloacate that space to cars, requiring about 20 times as much road space per person?

    “There’s just not enough room” everyone would shout. “What – if that’s not daft enough, you also want to use more than half the road space just to store those cars when not being used? Are you mad? We’d have to knock down half the city to make room! Its just not a realistic idea!”.


  5. Mike Adams says:

    There remains a huge number of people who refuse to see that they are not held up by congestion, they are part of the congestion. To sit in your car blaming all the other cars is the mark of a fool.

  6. Scott Davies says:

    The brilliant Jane Jacobs spoke about this phenomenon back in the 50s, and its been convincingly established in countless studies ever since. Yet people are still utterly convinced that the level of traffic and mix of modes is somehow fixed. It’s a triumph of unthinking instinct over evidence.

  7. Ian says:

    I used to work on an “advanced” traffic signal control system about a decade ago. Highways authorities would install it to increase capacity at a junction, and for a while queues would reduce… but it would often not be long before people realised this, and the junction returned to its previous congested state – just with a higher number of cars per hour using it (with all that meant for levels of pollution, etc.).

    • Matthew Phillips says:

      Ian, do you have some examples or evidence you can point me to which might help convince our local authority? They are about to install advanced traffic light control of some roundabouts to reduce congestion and improve air quality, but in the process the number of lanes on the roundabouts will increase, making them no-go areas for cyclists (not that they ever were great on a bike). The cycling facilities planned are all shared use footways, probably too narrow for comfortable use by pedestrians and cyclists. We have proposed various changes, but we are told that better cycle lanes will only cause unacceptable congestion.

  8. AndyC says:

    This is slightly off topic, but related. Since 2003 the North Terrace of Trafalgar Square has been a ‘Place’. And, among others, has been colonised by Street Performers performing in front of the National Gallery. This has obviously become possible because of the ‘pedestrianisation’ of the North Terrace, and was a gradual process that we had to fight for (through the courts), but now is an “official” street performance space, accepted and designated as such by Westminster CC and the GLA. In other words, what was once unthinkable, has become mainstream, although it took 12 years to get there.

    Meanwhile, as a Street Performer (unicycle if you must know) I would love to be able to perform in the ‘Place’ that is Exhibition road, right by the museums, but there just seems to be too much traffic.

    However, on the plus side, as a resident of Kensington and Chelsea, with my resident’s parking permit, I can park there whenever I like.

  9. paulc says:

    what continues to astound me is that there is currently a major program of roadworks taking place in Cheltenham where roads are closed for several weeks in turn for sewerage works and yet no-body is making any effort to learn from these quite long term closures what happens to traffic…

    the roads being closed are in some cases quite major ones as well

    there’s also one road in Cheltenham that is about to be closed to through traffic for an amazing 85 weeks, yet again, there is no hint of before, during and after surveys being made…

  10. Clive Durdle says:

    Don’t forget the science! Chaos, non linearity, strange attractors, flow …

  11. Jenny Barnes says:

    If you had a city that consisted entirely of road space, no-one would want to use the roads (or is that a motorway?). There must, therefore, be a point between the percentage of useful city in London and No usable city (ie 100% road space) where there was enough road space for everyone’s desires? I don’t think it would be a very nice place, though.

    • michael says:

      I suppose one could imagine starting at the other end – nothing but road surface – and then progressively adding buildings and accompanying people and economic activity, till it reached this ‘sweet spot’.

      The problem is that with the finite space available you would only be able to fit in a tiny fraction of the city’s current population when you reached that ‘optimum’ point. Where would everyone else go and what would generate the wealth to make the place viable?

      Now, if we repeated the exercise based on a more space-efficient mode of transport, that sweet-spot would coincide with a far higher population level.

      • Mark Williams says:

        No need to imagine; just read Sir Patrick Abercrombie’s reports. Where will all the displaced people go? New towns (big ones) all over the green belt! No consideration of space-efficient modes, of course—as he, like Sir Colin Buchanan later, was only interested in [single-occupant?] motor cars at >8m² a pop. `Progress’, you see…

  12. Naren Srem says:

    Nice article! Thanks for always taking care about this matter.

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