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.