what cyclists can do for carbon emissions

With all the cyclists in Cape Town last weekend for the Cape Argus Pick 'n Pay Cycle Tour, I did a bit of digging around to see what estimates have been made of how cycling could reduce carbon emissions in the city. Here’s what I found.

A survey of learners at 14 secondary schools in the Mitchell’s Plain suburb of Cape Town (The ICLEA Cities for Climate Protection report, Bicycle Infrastructure: Mitchell’s Plain Project, June 2004) showed that 66% walk, 2% use the train, 8% travel by car, 11% travel by taxi, 3% travel by public bus, 9% travel by school bus, and 1% travel by other modes. Calculations of CO2 (equivalent) emissions from these trips show that they produce 53 tons per annum – 31 tons from car travel, the rest from bus and minibus taxi travel.

CapeTown's total annual CO2 (equivalent) emissions from all sources have been estimated to be in the range of 17 to 21 million tonnes*, so the school sample's impact appears small - but the survey represented only a small portion of all Cape Town schools, and of course there are many other types of trips that could also be made by bicycle, given the right conditions.

It is interesting to note that the total distance travelled by the sample of 3,674 surveyed learners was 1,130 km, or an average of 307m each. The 2,425 walkers each travelled an average of 387m – higher than the average for all modes combined! Over the years, learners seem to be using motorised trips for shorter and shorter trips, which suggests that – for whatever reasons – they are not finding it convenient to walk or cycle, and this is worrying. In the survey, 50% of respondents identified safety (road safety or personal security) as impediments to travel.

While cars carry only 8% of the learners to and from school, they are responsible for 58% of emissions** from the full sample of trips. Scenario testing showed that a 1% increase in bicycle use (with a 1% decrease in motorised transport) would reduce school transport emissions by 11%. (Source: Sustainable Energy Africa, Bicycle Feasibility Study Report, Greenhouse Gas Emission Analysis, March 2004.) In other words, a relatively minor change in behaviour can result in a significant reduction in emissions. And the potential for transformation is even greater in the wealthier suburbs, where fewer children walk to school.

*The Mitchell's Plain report quotes Cape Town's total annual emissions as 17 million for 2003, while the Climate Group estimates 21 million tonnes for the same year.

**Emissions modelling for the study was carried out using the South African edition of the CCP Greenhouse Gas Emission Software, which uses carbon emissions coefficients for various fuels based on IPCC data. The software is available from Torrie Smith Associates.