How much carbon emissions could be saved if we could convince more people to cycle instead of using their car?
This question came to my mind after reading a blog post by Felix Salmon. Felix runs a very good financial blog for Reuters and took issue with John Cassidy’s silly rant against bike lanes in New York City (as I did) . However, one point Felix raised in his blog really surprised me. He wrote:
The amount of pollution emitted by today’s cars is actually pretty low, while the amount of congestion they cause is enormous. I’d be happy to introduce Cassidy to Charlie Komanoff one day, the guy who’s actually done all the hard empirical math on this question. The pollution-related negative externalities associated with Cassidy’s drives into Manhattan are tiny, while the congestion-related ones are enormous — well over $100 per trip.
Can this really be true? Is pollution not an issue anymore with regard to cars? Unfortunately I was not able to open Komanoffs’ Excel file Felix is referring to on his blog. This is why I tried to answer this question myself doing some back-of-the-envelope calculations. I only focused on carbon emissions and took London as an example.
According to the latest “Travel in London” report by “Transport for London”, on average Londoners made 28.4 million journeys per day in 2009 (chapter 2, page 40). 10.8 million of them (38%) were done by car, motorcycle or taxi while 0.5 million (1,8%) were done by bike.
Total carbon emissions in London were 44.7 million tons per year. 9.8 million tons (22%) are emitted by ground based transportation. (“Travel in London”, chapter 7) 45 % of those emissions (4.4 million tons) are caused by cars, motorcycles and taxis – 0,0121 million tons per day. Hence, the CO2 emission of an average car journey in London is 0,001126 million tons of CO2.
Let’s assume mayor Boris Johnson tomorrow will find the golden bullet for getting his cycling revolution going and 920.000 daily car journeys would turn into bicycle journeys. The share of cycling would jump to 5%. That’s the current share in Düsseldorf and Zürich and London’s official goal of Johnson for 2026 (!).
Provided I got the math straight per year this would reduce carbon emissions by 0,38 million tons, 4% of all ground based transportation but only a mere 0,8% of all carbon emissions in London. That’s merely a drop in the bucket.
What would happen if London would turn into Berlin where 13% of all journey are done by bike? We would have 3,2 additional bike journeys per day. On a yearly basis they would save 1,3 million tons of CO2 (2,9% of all carbon emissions in London)
The numbers are getting more impressive if you assume London would turn into Amsterdam with regards to cycling. In the Dutch city 22% of all journey are being done by bike. For London this would mean 5,7 additional bike trips per day and 2,4 Million less CO2 per year. Total CO2 emissions would shrink by 5% per year and the emissions of ground based transportation would fall by 24 %.
Unfortunately such a scenario is highly unlikely.
Even if the modal share of cycling in London would jump to 22%, car usage probably would not fall in the same extent. 5.7 million fewer car journey in London would mean that the modal share of cars would fall to 18%. Even in Copenhagen, which is seen as a role model for a cycling friendly city with 36% of all trips done by bike, private motor vehicles still have a share of 26%. (In Amsterdam it is 44%.)
Amazingly, Felix really seems to have a point.
Cycling Intelligence 
I think you’re confusing some of your figures. The wikipedia link that you use gives “modal split of journeys to work”, not of all journeys. What’s more, I’ve yet to see any published Dutch figures which relate only to commuting journeys. That’s not what they measure. As a result, I’m not sure I trust the source of this information. None of the references given are Dutch.
Usually, the overall rate for all types of journey within Amsterdam is given as around 37% to 38%. It has been widely reported that there are now more bicycle trips than car trips in the city.
On the other hand, many sources of information about CPH inflate its figures for the purpose of marketing the city. I wrote about this a little while back, showing the actual figures presented by the city administration itself, which are somewhat different to the marketing figures.
These show that more than half of all journeys in CPH are by car and around 20% are by bicycle. In recent years, the population has become more scared to cycle, those quoting impressive figures have fallen back on only presenting the “commuting” numbers, thereby not having to concern themselves about a lower rate of more vulnerable people cycling. When I wrote my piece I extrapolated the likely overall cycling rate as around 22%, and the head of the city’s bicycle programme wrote to say that he agreed with me (his reply is in the comments beneath the blog post).
You need to be careful with sources for some of these things.
David, many thanks for your comment. Indeed I did not realize that the figures from Wikipedia relate only to commuting journeys and not to all journeys. I’m going to add a correction, soon.
Olaf,
I would suspect that from an environmental damages perspective, CO2 is not the main issue. The big harms associated with vehicular traffic, especially in cities, are NOx and particulates, both of which are ground level ozone precursors. New cars are definitely better than older cars when it comes to CO emissions but they tend to make more NOx. Further the fleet on the roads is a mix that changes quite slowly. All these pollutants have been shown to cause premature death, asthma (both childhood and adult), lung cancer, etc…
Your point that mode shift to bicycles only leads to small decreases in total emissions is of course correct. My point is that the marginal damages are higher than you are likely crediting by focusing solely on carbon.
Best,
Michael
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I have read the cycling does contribyute ghg emissions due to ghg emissions in food production, distribution and burning for food in the body. This has been calculated as equivalent to 100mpg gasoline car for meat eating cyclist and to a 200mpg gasoline car for vegitarian cyclists. I would guess that an electric bicycle produces less ghg emissions than a human powered bicycle, especially if electricity source is hydro power or other green power source like wind or solar.