There can be no doubt that the 21st century has witnessed a radical renaissance of Mexico’s capital, Mexico City. Where once its rapidly growing population (now around 21 million people) and precarious geographical positioning (at 2,200m above sea level, atop an unstable lake basin) were creating severe shortages of clean water, electricity, housing, and sewage facilities, a series of economic and cultural changes have transformed the city into a modern cosmopolitan metropolis.
Like many cities around the world – from London to Beijing, Paris to Delhi – Mexico City does, however, continue to battle toxic air pollution; a filthy, thick layer of smog which blights the skyline and fills the lungs of millions of residents every day. Globally, the World Health Organization estimates that around three million deaths annually are due to ambient (outdoor) air pollution, and only one person in ten lives in a city that complies with the WHO Air Quality Guidelines.
The topography of Mexico City is particularly harsh; its location within a ring of rangy mountains traps the tiny particulate matter, carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2), nitrogen oxides (NOx) and other toxins, preventing them from escaping into the wider environment. This results in particulate levels (PM10) that are three to four times higher than New York, Los Angeles, or São Paulo. As with other global cities, there are a variety of sources for these pollutants, but one of the key culprits clogs the city streets every single day: the car. Vehicles in Mexico City are believed to be responsible for 99 per cent of carbon monoxide, and 82 per cent of nitrogen oxide emissions.
Recognising the seriously adverse effects that millions of private cars were having on the megacity’s atmosphere, Mexico City became one of the first in the world to implement driving restrictions based on individual car licence plates in November 1989. Known as Hoy No Circula, the scheme bans drivers from using their vehicles one day per week, depending on the last digit of the vehicle’s plate (for example, vehicles with a license plate ending in ‘5’ or ‘6’ cannot not be used on Mondays), and drivers caught violating the rules (they are fairly easy to spot, given the police know exactly what number to look out for each day) must pay a hefty fine and their vehicles are impounded for 48 hours. In July 2008, the scheme was extended to include Saturdays, and plenty of cities subsequently followed Mexico City's example; more than 145 million people now live in cities with license-plate based driving restrictions, most recently Delhi in January 2016.
“Drivers everywhere have a revealed preference for fast and convenient transportation, so it can be difficult to get them to switch to public transportation”
Unfortunately, the effects of the ban appear to be far less promising than such a successful global take-up might otherwise suggest. A 2008 study concluded that ‘there is no evidence that the program improved air quality,’ stating that it ‘engendered a relative increase in air pollution during weekends and non-peak weekdays,’ but that there was ‘no evidence of an absolute improvement in air quality during any period for any pollutant’. Now, a follow-up study by the same institution, the Haas School of Business, University of California, Berkeley, has examined the Saturday extension, and discovered that, despite hopes the scheme would reduce air pollution levels by over 15 per cent, the expansion had virtually no discernible effect.
‘Saturday driving restrictions are a flawed policy,’ says Lucas W Davis, an associate professor at UC Berkeley’s Haas School of Business, and lead author of the study. ‘It’s a big hassle for people and does not improve air quality. People have found other ways to get around the driving restrictions. Some purchase multiple cars, others take taxis or Uber.’
Davis analysed hourly air pollution data from 29 monitoring stations around Mexico City between 2005 and 2012 and discovered no noticeable decrease in all pollutants as a result of the driving restrictions. Analysis of public transport rider numbers – on city buses, electric buses, and light rail – also revealed no significant increase as a result of the ban. He argues that residents continued to drive, just in alternative cars, or by using ‘taxis’ such as Uber.
These conclusions cast something of a shadow on the effectiveness of licence-plate driving restrictions around the world to combat life-threatening air pollution, and, in a small way, the larger issue of climate change. Davis doesn’t entirely despair of the usage of such measures, however he points out that it is far from a one-size-fits-all solution to this worldwide problem.