James Schneider  

Paris Flirts With Banning Cars Based on License-Plate Number

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Recently, a lack of wind and rain has inflicted unusually high smog levels on Paris. On Monday, March 17, Paris combatted the dangerously high levels of pollution by barring cars with even-numbered license plates from the roads. The intent was to ban even- and odd-numbered license plates on alternate days until the smog returned to safe levels. However, the city removed the restrictions after just one day.

Other cities have imposed license-plate bans to address long-term problems with poor results. The best evidence on the effect of license-plate bans comes from Mexico City's Hoy No Circula program, which has been in effect since 1989. This program bans most cars one day each week based on the last digit of the car's license plate number. Hefty fines guarantee that the program enjoys near universal compliance. Unfortunately, Hoy No Circula seems to have increased pollution instead of limiting it. Not only did it not decrease pollution during the regulated weekday, daytime hours, it actually worsened pollution during weekends and nighttime hours. The latter is to be expected. Many people probably shifted some of their driving to hours outside the ban. Other evidence shows that the program failed: it did not increase the use of public transportation, and it did not decrease the sale of gasoline.

In general, policies that closely target the final objective have a better chance of success. Many factors determine the pollution caused by a driver; however, the car's license plate number is certainly not one of them. License-plate bans seem tailor made to create perverse unintended consequences. Given that the predictable nature of the driving restrictions, there existed a costly but straightforward way to completely circumvent the driving restrictions: buy a second car with a license plate that allowed driving on the day of the week that the first car was banned.

Both new car sales and car registrations increased. However, the majority of new car registrations were for used cars. Economic theory suggests that someone who is forced to buy a second car effectively becomes poorer. These people will on average drive older cars. Likewise, the less you use a given car, the less advantage you receive from owning a newer car. Older cars are generally associated with higher emissions. With higher emission vehicles, a license-plate ban could reduce driving without actually reducing pollution.

Despite their other failings, license-plate bans might at least sound like a fair way of allocating the burden of reduced driving. However, when you consider the impact of buying additional vehicles, it's distributional properties look pretty poor as well. Many drivers obviously can't afford to buy a second car, and many of the rich already own two cars.

Other Latin American cities have followed Mexico City's example. Bogotá's program, Pico y Placa, bans most cars from driving two days a week. Bogotá's program is interesting in that once a year, they change the days of the week that a given car is banned. However, they do not change the grouping of license-plate digits. This means that the strategy of buying a second car continues to work. Someone who owns cars whose license plate numbers end in 2 and 8 can drive everyday of the week. Each year when the city changes the restricted days, this pair of cars will continue to provide daily access (each car will just be used on different days). Much like the experience in Mexico City, Pico y Placa seems to have increased the car fleet without increasing overall air quality.

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COMMENTS (5 to date)
Andrew_FL writes:

Why couldn't you just exchange license plates with someone else, too? What are the odds you get checked to see if your plate really is registered for your car?

Come to think of it, people could counterfeit plates, too, I suppose.

Jameson writes:

So what's an alternative? It's pretty lame to just point out what a bad idea one strategy is without proposing another. If you were consulting the government of Paris, how would you deal with the recent pollution problems?

Matt writes:

Jameson: I think the obvious answer is that if you want to reduce pollution, you have to tax pollution itself to disincentive it. If you want fewer cars on the road, a congestion charge for driving in the city, a higher gasoline tax, or a tax based on miles driven would all work.

Banning cars based on license plate numbers is an indirect method to try to get people to drive fewer miles in their cars and apparently it doesn't work.

Damien writes:

I am not sure whether the Mexican evidence is relevant to what Paris was trying to do. The point of the ban was not to permanently lower emissions but to have temporarily lower emissions because of exceptional meteorological conditions. There also was no "about-face": the restrictions were never meant to last more than one or two days and were lifted when air quality had improved, as planned.

Such measures can be effective if they remain exceptional. No-one will buy a second car in order to avoid a licence-plate ban that occurs once every 17 years. Especially since the French do not get to pick a licence plate number and thus only have a 50% chance of getting the right numbers.

The evidence shows that it worked: congestion was cut by 50%. It would be silly to suggest implementing this as a year-long solution. But it served its purpose in this particular case. Note that it "closely target[ed] the final objective", which was to have a one-time decrease in emissions and that there were no "predictable nature of the driving restrictions", since it was announced one day before the ban and may not be done again in the next 17 years.

James Schneider writes:

@ Damien Thank you for your comments. When I first wrote this post, the initial source I saw (not the NPR article) implied that it was in response to disgruntled motorists. The extra googling I did inspired by your comment led to articles which included the fact the government claimed the program was a success. I tweaked the post a bit in response.

So are you saying that in France a car gets a different license-plate number every time it is sold?

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