Today it doesn't circulate


Unintended consequences have been knocking around since the dawn of humanity. But they only became a prominent feature of the social sciences in the 1930s, when American sociologist Robert K. Merton coined the term in his seminal essay on social action.

Unintended consequences transcend theory. They give us a powerful way of examining the world, a kind of superpower x-ray vision that exposes the complex relationship between seemingly disparate social, political and economic forces.

Examining the second order, third and n-th order effects of intentional action helps us to understand more deeply how our world works. It enables us to spot opportunities - and threats - whilst other people are getting bogged down in the first order, the obvious, the here and now. An appreciation of unintended consequences helps us to predict the future.

This article is the first of many. I want to expose the unexpected and often perverse relationship between intention and effect through a series of obscure (and seemingly disconnected) historical anecdotes. From time to time, I’ll talk about the future too, speculating that current events might result in very different outcomes to those anticipated by the media, the markets and the tech-obsessed masses.

Let’s start with something that everyone hates. Traffic.

Nowhere on earth is more notorious for traffic than Mexico City. In order to address the problem and reduce air pollution, in 1989 the government introduced a traffic-calming policy aptly named Hoy No Circula (“today it doesn’t circulate”).

Here’s how it works. Certain days are designated as "no drive days". If your car’s plate number ends with a certain digit, you cannot drive. On Mondays, plates ending 5 or 6 are banned from roads. On Tuesdays, 7 or 8. And so on. Hoy no Circula began in late 1989, prohibiting the circulation of 20% of vehicles from Monday to Friday. The program was supposed to apply during the winter when air pollution is at its worst, but it was made year-round at the end of 1990.

At the time, this seemed like an ingenious solution to the city’s traffic nightmare, one which would drastically reduce the number of vehicles on the road and slash air pollution. Indeed, the programme was initially successful in reducing pollution, with carbon monoxide levels dropping by 11%.

But then, the exact opposite happened.

To circumvent the new rules, the good people of Mexico City bought more cars. A thriving trade in second hand vehicles sprang up, with commuters buying different plates so they could travel every day. The World Bank observed that “A ban restricting each car from driving on a specified weekday is found to have increased total driving in Mexico City”. That’s an understatement - the number of cars skyrocketed, and because they were old vehicles with poor environmental standards, pollution actually increased.

A 2007 study by the University of Michigan found that "the policy has engendered a relative increase in air pollution during weekends and non-peak weekdays, but there is no evidence of an absolute improvement in air quality during any period for any pollutant." The long-term impact of the scheme has been a 13% rise in carbon monoxide levels.

A creative, bold, well-intentioned solution to a very serious problem exacerbated it. Licence plate schemes have operated in several major cities over the years, including Athens, Beijing and Mexico City. But drivers continue to circumvent restrictions by buying cheap, inefficient cars with opposing number plates, which means many schemes have had an adverse impact on air quality. To make things worse, as these policies tend to make no distinction between old and new vehicles, there is no incentive for motorists to invest in cleaner cars.

This somewhat depressing outcome doesn't mean we should give up trying to reduce emissions. In fact, evidence suggests that low emission zones and and congestion charges are effective at reducing concentrations of dangerous particles and chemicals which cause more that cause 1.3 million premature deaths in cities every year.

The failure of Hoy no Circula reminds us of the need to consider the unintended consequences of our actions. The world is a complex system, people are complex systems, and we are still learning about ourselves and the impact of our decisions on a collective and individual level. We have to try.

Edward Rhys