What's the Greenest Way to Get Around Town?

There was predictable outrage among the active transportation types on Twitter when BMW ran a silly poll on World Environment Day:

Nobody was impressed that BMW considered its cars to be "super sustainable" but also, that it didn't include choices for walking, biking, or e-biking. In fact, the question of what the best way to get around town was answered by Seb Stott of British biking site BikeRadar in an October 2020 post—and it wasn't a super sustainable BMW.

Emissions from Fuel Consumption

This is not so simple: One has to compare fuel consumption. For cars and transit, it's not so complicated, fuel economy in kilowatt-hour for electric power or fossil fuel for gas-powered transport is well known. For bikes and pedestrians, food is the fuel. Stott writes:

"The emissions from producing the extra food required to ‘fuel’ the cyclist per kilometer. This is done by working out how many extra calories it takes to cycle each kilometer, and multiplying it by the average food production emissions per calorie of food produced."

This is complicated and controversial. Stott notes there are studies concluding that people do not eat more food when they exercise and people's diets often change when they take up exercise. But there is a study from the European Cyclists Federation—"Quantifying CO2 savings of cycling"— looked into this and concluded:

"An average cyclist travelling at 16km/h and weighing 70kg will burn 280 calories per hour, compared to 105 calories per hour if they weren’t cycling. So an average cyclist consumes 175 extra calories per 16km; that works out at 11 calories per kilometre."

However, much depends on dinner. Using data from Treehugger's favorite source, Our World In Data, I calculated the impact of different diets to figure out the carbon dioxide emissions. Eleven calories of beef will produce 400 grams of CO2; 11 calories of rice, tofu or root vegetables will produce 12.76 grams of CO2. Essentially, running a bicycle on steak is worse than driving. However, Stott uses what he calls an average European diet and comes up with 16 grams of CO2 per kilometer.

It's hard to know if this is a reasonable analysis because these days almost everyone eats more than they actually need since portion sizes are so out of control, with the average American male eating 3,600 calories per day—24% more than they did in 1961, according to the FAO. In the electricity world, it would be considered surplus or wasted, and the carbon has been emitted whether it goes to pushing the bike or the waistline.

E-bike riders burn fewer calories per kilometer because they are not working as hard, burning only 4.4 extra calories per kilometer, with Stott concluding that they emit. 6.3 grams of CO2 per kilometer.

There is also the embodied carbon, the emissions that come from the making of the vehicle. You then divide that by the estimated number of kilometers or miles it will get driven, giving you the embodied carbon emissions per kilometer. They also use electricity, added to the food emissions, still come up lower than conventional bikes.

Walking is even less efficient: "An average 70kg person walking at 5.6km/h (3.5mph) on level ground will burn approximately 322 calories per hour, compared to 105 calories per hour if doing no exercise. That’s 217 extra calories per hour (or per 5.6 kilometres travelled) or 39 calories per kilometre." Converted to CO2 using the same European diet standard, that comes out to 56 grams of CO2 per kilometer.

Embodied Carbon from Manufacturing of Bikes

Bikes are light, but the carbon footprints of the materials they are made of varies widely. Where they are made matters too: Chinese steel is a lot dirtier than recycled steel. Virgin aluminum has a footprint 20 times that of recycled, and Chinese aluminum has twice the footprint of Canadian or European aluminum. It is all over the map, so Stott uses the European Cyclists Federation's estimate of 96 kilograms of CO2 per bike frame and divides that by the average 19,200 km lifespan of a bike to get 5 grams of CO2 per kilometer. E-bikes have a battery as well, which has a carbon footprint of about 34 kilograms, adding 2 grams per kilometer, and add another 1.5 grams of CO2.

Totaling it all up, Stott comes up with 21 grams per kilometer for the conventional bike and 14.8 grams per kilometer for the electric bike.

In a famous Canadian tax law case, the late Alan Wayne Scott, a bike courier racking up 39,000 kilometers a year, challenged the government which allowed drivers to deduct gas but didn't let bike couriers deduct food. The court found in his favor, noting that “just as a courier’s automobile requires fuel in the form of gas to move,” Scott required “fuel in the form of food and water.”

So I assume that a case can be made for including the food in this analysis, but I am not convinced, given the way we eat. In my own analysis for my recent book, "Living the 1.5 Degree Lifestyle," using different sources, I used 17 grams per kilometer for the e-bike and 12 grams per kilometer for the regular bike, determined by weighing my Gazelle and (it's heavy) and using Bosch data on electricity consumption.

What About Cars?

Treehugger has covered the question of the lifecycle emissions of electric cars versus gasoline cars many times, so I will not go through Stott's calculations in detail. He uses data from the Union of Concerned Scientists:

"According to the UCS, manufacturing a mid-size electric car results in 7.7 tons of CO2e (about 15 percent more than the equivalent average-sized petrol car). If we assume the car is driven for 157,000km, as we did for the internal combustion car above, that corresponds to 49g CO2e per kilometre from manufacturing emissions."

It is a six-year-old report and 7.7 tons is really low. He estimated the total emissions from an electric car at 90 grams per kilometer. In our post, I estimate the emissions of a Tesla Model 3 using the current U.S. power mix to be 147 grams per kilometer, and the emissions from a Ford F150 Lightning may well be triple that.

Stott produced this bar chart that shows the e-bike being the best, with the electric car actually being better than walking. I do not understand why the electric car is showing as less than 50 when in the copy, he says it is 90.

My version, using data from my research, comes up looking a bit different. Transit is lower because I am using streetcars and subway that run on electricity, and if you discount food as fuel, then walking obviously wins and cycling comes second. I am convinced that his graph also doesn't represent electric cars properly. (I tried to contact Stott and BikeRadar, but his email bounced back twice so I couldn't verify this.)

But whatever way you look at it, the best way to get around town is to walk or to bike, whether on a bike or an e-bike. And no, that BMW is not the best way to get around town.