Why licence plate bans don’t cut smog

Licence-plate driving bans such as the one implemented in Paris this week are not the solution to urban air pollution, according to analysis of recent data. In fact, arbitrary restrictions have been shown to make air pollution worse in the long term.

Long-running licence plate schemes operate in many cities, including Athens, Beijing and Mexico City. Some ban cars every second day, others once a week. But drivers inevitably circumvent restrictions by buying cheap, inefficient cars with opposing number plates according to Lucy Sadler, who runs the Low Emission Zones in Europe website. This means some schemes have had an adverse effect on air quality.

“Certainly, in terms of comparison between low emission zones and odd-and-even number plate schemes, it’s a no-brainer,” Sadler said. “There is lots of good evidence saying low emission zones have a good impact on air quality and health. That’s robust and well researched.”

“As the [licence plate] traffic restriction can also affect cleaner vehicles, there is no incentive for motorists to invest in cleaner cars with particle filters or catalysts,” said Martin Lutz, from Berlin’s Department for Urban Development and Environment.

Lutz agreed that low emission zones (LEZs) , hundreds of which now operate in Europe since Stockholm implemented the first in 1996, are a more effective way of decreasing the contribution of traffic to air pollution. LEZs ban inefficient vehicles from city centres, forcing drivers to upgrade their cars.

On Monday, the French government reacted to dangerous levels of pollution by requiring cars with licence plates ending with an even number to stay off the road. Nearly 4,000 fines of €22 were issued to drivers who flaunted the restriction. It was the second time Paris had implemented a short-term ban in response to high smog levels; the city’s air quality authority, Airparif, says such measures are effective in combating pollution emergencies.

But Ben Barratt, from King’s College London, said the effect of short-term actions is difficult to assess. “The weather changes all the time, the emissions change all the time and trying to pin down whether a particular emergency scheme works or not is hard.”

Short-term schemes also cause mass disruption and dissatisfaction, Sadler added. “The impact to society and to vehicle operators is horrendous. Suddenly, tomorrow, you’re not allowed to move.”

Research on the impact of licence plate-based schemes is rare, but an analysis of existing data shows a mixed set of results. Conversely, LEZs and congestion charges, which encourage drivers to use public transport and shift to more efficient cars, are proven to reduce concentrations of dangerous particles and chemicals which cause more than 1.3 million premature deaths in cities every year.

Asked if it was fair to place the burden on drivers, particularly low-income drivers, Sadler said those who earned less tended to use public transport, and the responsibility for the pollution created by cars should ultimately rest on the person at the wheel. “If somebody’s polluting, why should society subsidise that? In air pollution, the polluter pays in principle.”

But according to Barratt, LEZs should be used alongside inner-city congestion charges, as they are in London: “You have to take the vehicles off the road, rather than just try and make them cleaner. So something like congestion charging, where you’ve got a marked decrease in the number of vehicles on the road, is preferable to something where you’ve got the same number of vehicles, [even if] those are cleaner.”

City traffic case studies 


The Hoy No Circula (‘today it doesn’t circulate’) was introduced by Mexico City in 1989 to combat rampant air pollution. The city bans cars for one day per week, depending on the last number of their number plate. On Mondays five and six don’t drive, on Tuesdays it’s seven and eight, and so on. The programme was initially successful in bringing down pollution levels, with carbon monoxide (CO) dropping by 11%. But residents began buying second cars (often old inefficient ones) to get around the ban. The long-term impact of the scheme on CO levels has been a 13% rise.


Bogotá’s Pico y Placa (‘peak and plate’) banned cars from driving during the peak traffic hour, two days per week. The Colombians sought to improve on the Mexican model by switching the combinations of days and numbers every year, making it harder to circumvent by buying another car. The policy has failed to deliver clear benefits in air pollution. Restrictions have been tightened periodically, with some of the changes leading to reductions in CO and airborne particles. But one study found most of the major pollutant concentrations were worse because drivers were driving in off-peak hours and driving more to get around the measures.


During the 2008 Olympic Games, Beijing banned cars on the basis of odd and even numbers, similar to the French ban this week. In conjunction with some fortuitous rain and the shutting down of the factories and industries that cause much of Beijing’s pollution, the ban drove airborne particulate matter concentrations during the Olympics down by 20%. After the Games, the Beijing authorities kept a one-day a week ban in place. But this, like other long-term licence plate bans, has had a limited effect on air pollution and encouraged drivers to buy second cars.


The Swedish capital implemented its LEZ in 1996. Vehicles are banned from these zones if they fall below certain EU emissions standards . The Stockholm LEZ brought emissions of nitric oxide (NO) and nitrogen dioxide (NO2) down by 20% and particulate emissions down by half. The effect of this on the air quality was noticeable, with NO and NO2 concentrations down 1.3% and particulate concentrations down 3%.


A £5 congestion charge to drive on London’s innermost streets was implemented in 2003. Studies showed emissions of dangerous pollutants – NO, NO2 and small particulate matter (PM10) – were reduced by 12%. The charge is now £10.

In 2008, Transport for London introduced an LEZ, which governs the efficiency of lorries, buses and coaches for the whole of Greater London. The zone led to a fall of 20% in tiny particulate matter (PM2.5) but had no discernable impact on PM10 or NO2. Critics say London’s LEZ needs to include private vehicles if it is to be effective.


Implemented in 2008, Berlin’s LEZ bans all diesel vehicles and petrol vehicles without a closed loop catalytic converter. The effect on levels of diesel pollution, which is a known carcinogen , has been dramatic. Concentrations of diesel particulates have dropped by 14-22%. PM10 concentrations near main roads are down 3% and the number of days when the city’s air pollution exceeds European standards has fallen by four to 24 days per year.

Air of revolution: how activists and social media scrutinise city pollution

via Why licence plate bans don’t cut smog | Cities | theguardian.com.

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