Sunday, April 23, 2017

Commentary : The Environmental Impact of Pre-Ride Food Choice and Driving to a Bike Ride

This is an Earth Day special commentary that I wrote on my Facebook page. The post was inspired by a similar opinion post along the same lines written by Thorpe & Keith from the Keith Group. They provide a host of reasonable references from where the numbers were picked.

The environmental impact of "getting to a ride" by car is analyzed below. What is also interesting to think about is the environmental burden due to choice of diet, which makes big marginal differences depending on what you put in your mouth.

Attached below are some graphs from a simple estimation of CO2equivalent emissions for a cyclist commuting for a typical 100km weekend ride. 

In one set of graphs, the cyclist is assumed to have eaten a 'typical American' diet and vehicle emissions were derived from test data for assumed 90kph driving speed. 

In scenario 1, driving distance = 20km in a conventional 4 door automatic petrol engined 2L Honda Civic. 

In scenario 2, driving distance = 20km in an automatic petrol engined 3.6L Porsche Panamera 4 PDK (Euro 5). 

In scenario 3, I look purely at impact of driving a fuel efficient, ULS diesel powered 2L Skoda Octavia Hatchback (Euro 5) as support vehicle for the cyclist (commute to ride is neglected). However, due to support function, the Skoda will be driven the 100km at a slow speed matching the cyclist (let's say 30-33 kph). Only the diet for the cyclist is taken into account, while that of the driver's is neglected.

Please note that life cycle environental impact of production of the vehicles, the bicycles and the construction of a public road system that the cyclist and driver utilize are neglected in the analysis.

The comparison is interesting if you account for the slow speed fuel efficiency degradation of any conventional vehicle. If you assume a 15% fuel efficiency derate due to low speed vehicular losses in the Skoda, then on a per km basis, I believe it makes little difference to be driving a Civic fast to the ride or a Skoda slow as a support car - they are more or less equally polluting regardless of what the sticker fuel efficiency is.  Meanwhile, it is approx 30% more polluting to carry bikes on a Porche when driven at similar highway speeds as a Civic, no surprise there.

The takeway? Reduce driving, carpool if possible and keep the luxury car at home. When driving, drive at the sweet spot fuel consumption speed. In urban environments, it helps to live close to a cycle track.

And finally, reduce or eliminate the use of conventional fuel support cars on long rides as pollution is spread over a larger area. If that's not possible, choose lighter cars with smaller displacement engines and reduce the number of start-stops. Start-stops cause relatively more pollution than constant speed driving regime due to the repeated accelerations and decelerations the vehicle must go through.

What is also interesting is to look at the effect of the cyclist's diet for this ride. In the first set of graphs above, I have assumed the cyclist to eat a typical diet with a life cycle burden of 2.6 gCO2eq/kcal. The carbon intensity of that ride on that diet is an average of 30-40 times less than driving the respective cars on a per km basis. 

However, if the same cyclist chose to eat a high protein meat rich Paleo diet with a pollution burden of 5.4g CO2eq/kcal, the difference is halved. For example, in the case of driving the Civic to the Paleo fueled ride, driving is only 15 times more polluting than cycling relative to a normal diet. Stunning if you think about it.

What I'm pointing to (as others have pointed out) is that on a gram of CO2eq per km basis, the high meat rich diet can be worser off than the transportation fuel in terms of the embedded carbon intensity (what goes into the production of the fuels). The reason can be attributed to the carbon intensive nature of raising cattle to produce beef. 

So the takeaway from this second analysis is that when possible, substitute lesser energy intensive forms of protein in your diet for fueling the ride. And while it, keep the beef away from the support car driver!

Post script : 

Just because cyclists reduce or avoid consuming a meat rich diet does not necessarily mean that the product will not be produced. Supermarkets will still carry the meat and someone else will buy and consume it. So on a global level, perhaps we'll see the same environmental burden of meat consumption.

However, if you account for the fact that products are sold because of relative consumer demand, if one segment of the market shifts outlook and reduces meat consumption, we can assume that somewhere else in the chain, production maybe cut. I'm not sure if its as simple an analysis as that and what timescales it takes to shift mindset overall. Something to think about though.

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