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In Bogota Car-Free Isn't Pollution Free

An unusual calm on Bogota’s streets. Photo by Pattoncito from Flickr.

On Thursday, February 7 Bogotá held its 8th annual car-free day during which 14% of the population left their private cars at home and walked, cycled, and took mass transit to get around Colombia’s capital city. The car-free day is a bold effort to give people the chance of experiencing how nice the city could be without the 1.2 million private vehicles that ply Bogota’s streets every day. Following Bogota’s lead the car-free movement is spreading throughout the world, but still, this Andean city is the only one of its size that actually enforces its efforts, slapping $118 fines on any vehicle breaking the ban.

The Colombian newspaper EL TIEMPO reported a 45% reduction in carbon monoxide, an improvement attribute to the absence of private cars. This reduction, while important, was overshadowed by a 42% increase in particulate matter. Particulate matter is inorganic particles caused by diesel engines, brake and tire friction, wood burning factories using heavy fuels and coal, and forms indirectly in the air from SOx and NOX. Particulate matter has serious effects on the human respiratory system, and is especially harmful to children, the elderly and people with breathing problems. It is also one of the leading causes of bronchitis and asthma. At typical concentrations, particulate matter has approximately the same impact on human health as carbon monoxide. However, per equal mass emitted, it has between a 10 times (if its from brakes and tire friction) and 1000 times (if its from diesel engines and SOx) greater impact on human health than carbon monoxide.

For Bogotá, the really important question is whether the particulate matter which increased during car-free day was from brakes and tires or from diesel engines. If it was from breaks and tires then it will be removed quickly from the atmosphere, and we could argue unequivocally that car-free day improved human health. However, if it’s from diesel engines and Sox – as it is believed to be in the case of Bogota – then the increase in particulate matter may have outweighed the benefits from reduced levels of carbon monoxide.

From a public health perspective, the car free day might not have been as beneficial as expected, especially considering that Bogotá’s regular carbon monoxide concentrations are in line with international standards. According to Eduardo Behrentz, Director of the Center for Environmental Engineering Research at the Universidad de los Andes in Bogotá, “In short, in terms of local pollutants, the car-free day is not such a good idea. What I have always argued is that this event is a quite interesting civic experiment that promotes discussions about sustainable development and environmental protection.”

Crowds of people rode their bikes to work. Photo by Pattoncito.

I could not agree more with Dr. Berenhtz. Yet I believe that it’s important to communicate that the expected environmental benefits did not materialize not because there were too many buses but because the buses run on fuel with an average of 1000 to 1200 sulfur ppm, one of the worst rates in Latin America. Once ECOPETROL, the Colombian national Petroleum Company, reaches its goal of reducing the sulfur content to 50ppm by 2009, I am confident that car-free day will improve air quality. As Sebastien Humbert, expert in Life Cycle Impact Assessment at the University of California at Berkeley, mentions,“Improvement in technology and fuel quality is a natural trend in most economies, which translates in buses having lower impacts in the future. Yet, reduction of private car use is not a natural trend at all, and that is where events like the car free day become protagonist;, in supporting rationalization of the private vehicle such that it does not outweigh the health benefits from improved public transit technology.”

There seems to be a consensus among transportation and environment experts that Bogotá’s annual experiment is worth it, even if the only outcome is elevating the topic of air quality into the public discourse. In my opinion Bogotá deserves to be applauded for being at the fore front of such a movement, one that provides the residents of Bogotá an opportunity to experience the sights and sounds of a car free city. Viva Bogotá!

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  • Until fuel cells are marketable they really aren’t a viable alternative. By trapping methane that escapes from landfills you can at least use a fuel that would otherwise be escaping into the environment.

  • Federico Torres

    I am proud of all the effort that my city Bogotá is doing in the Transport area.
    I am studying an MSc in transport at London and my dissertation is about the Bogotá Metro.
    I want to Contact Dario Hidalgo, if you read this can you contact me?

  • Nicolas

    Todd have you read that methane is one main reasons for global warming? Said fuel is as counterproductive as what Catalina states with regard to the possibility that the increased level of particulate matter coming from SOx or diesel negates the benefits of cars not circulating for a day. Gas and biofuels are all the rage these days but few have analyzed the equally negative effects these fuels have on the environment. Batteries? Check how poisonous lithium, cadnium and lead are. Sure we need to reduce our consumption of fossil fuels for both economical and environmental reasons, but if we do so, let’s change it for something better. Fuel cells are a better bet. Nothing better than knowing that your emissions are only water and vapor.

  • Juan Pablo: Buses can certainly be powered by gas (methane) engines, and – unlike with replicating a convenient energy for cars – the fuel only has to be available at bus depots. Methane can be from the ground (CNG) or as a waste product (biomethane or biogas). Only the latter is a renewable type of energy. Using biogas a city transport system can have energy independence. Biogas is not perfect – there are some issues with nitrous oxide.

    Sweden runs nearly 1000 buses on biogas, and I hope that more cities look into treating their waste as fuel. Biogas is actually most efficient for generation of electricity, but for transport that would mean an electrified network (not necessarily light rail or a metro, but just trolley buses.)

  • Juan Pablo: Cleaner diesel is good for the entire city, not just for the TransMilenio Buses. Even with the promised Metro, most of the transit users will remain in buses. See for example Sao Paulo, where its Metro only carry 7% of the trips even with a total extension of 105 km. Hence, clean diesel is a must, even with the construction of the Metro first line. On the other hand, it will be great to have cleaner fuels and vehicles in TransMilenio… but they come at a cost. Finally, the 30 Million per kilometer Metro figure is not real. Previous studies in Bogotá, and the international experience, indicate costs around 90-100 million per kilometer. Metro will bring benefits to a fraction of transit users in the city at an extremely high cost.

  • Juan Pablo

    Is it necesary that Transmilenio buses be impulsed by diesel engines? can’t they have electric or gas motors? Is a better diesel really better or is a subway (that does not pollute) better than that? last Transmilenio lane cost 27 million dollars the kilometre and a subway is around 30 million. Can’t we have cleaner air for just 3 million the kilometre? seems cost efficient

  • Catalina touched exactly the right point and brought the discussion to the dimension required: top agendas in air quality in Bogota are the reduction of sulphur content in Diesel engines (promised by the national oil company, yet to be completed) and a transport system that is not dependent on cars (something really difficult… but still in the works). It is not that the car free day is not good to the environment (it is, but not enough). Keep it up Bogotá!