Are bikes greener than cars? That was the question tackled in a recent post. Looking at the issue from the perspective purely of energy used to travel – the results were a little counter intuitive to most of us I think.
The big thing not in those calculations was the embodied energy and therefore carbon in both cars and bikes. Many people on this site argued it needs to be taken into account, and I don’t disagree with that. The inference was, I think, that taking this into account the bike would have a way lower impact – that bit I wasn’t so sure of. I’ve pulled together some figures now.
The original numbers looked at the energy expended by the rider and driver respectively of a bike and a wind powered car – it was only energy used for travel and surprisingly the wind powered car had a smaller carbon footprint. Far smaller.
But that ignores the ‘cost to build’ of each vehicle. Let’s add that in now.
The best estimates we could find for the ‘carbon cost’ of building an electric car are 6 Tonnes. The cost for a bike a miserly 63 kilos. The cost for a conventional gas burning car BTW is 4 Tonnes. So the wind powered car produces a lot more carbon on day one.
It’s hard to imagine that with a virtually 6 tonne headstart the bike is ever going to catch up to the wind powered car in a lifetimes use – but let’s see.
The tricky bit coming next is the number of miles and the number of years to assume each is used for. Cars drive many more miles than bikes pedal, it’s in the nature of the beast, as someone said here because you can do more miles easily, you do.
The average lifespan of a car in the UK is 14 years, the average annual mileage is 9,800.
It might be fair to assume a bike can also last 14 years, it might not. But even if the bike had to be totally replaced, it’s only 63 kilos which is negligible in the scheme of this – so it doesn’t matter if the bike can match the car for lifespan or not.
What about annual mileage? Not so clear. So here’s two scenarios:
10 miles a day (typical bike use?) and 9,800 miles a year (typical car use).
At 10 miles a day for 14 years:
The cyclist racks up 4.7 Tonnes of lifetime CO2. Or 0.09 kg per mile.
The wind car driver racks up nearly 6.4 Tonnes. Or 0.13 kg per mile.
(The petrol car is over 21 Tonnes BTW)
That’s if you use a car like you might use a bike.
How about if you use a bike like you might use a car?
At 9,800 miles a year for 14 years:
The cyclist racks up 12.7 Tonnes of lifetime CO2 . Or 0.09 kg per mile.
The wind car driver 7 Tonnes of lifetime CO2. Or 0.05 kg per mile.
(Petrol car 51 Tonnes…!)
The kg per mile figure for the cyclist doesn’t really change because the embedded carbon cost is so small, it’s lost in the rounding. For the wind car it drops significantly with mileage.
Two things I’d stress here. Cars and bikes are not apples and apples. We use them differently. Cars enable bigger distances and more travel – we take that opportunity. The Wind car wins easily based on the car use scenario of 9,800 miles a year and the Bike wins easily based on the biking scenario of some 3,000 miles a year.
Hang on a minute though, at 9,800 miles a year, that’s roughly 30 miles a day – is that a crazy bike use scenario? I don’t know, but it doesn’t look off the scale.
Second thing to stress – these figures are for energy used by rider/driver and vehicle – and they include carbon embedded in the making of each vehicle. They don’t include hospitals and roads and stuff… (And no, I’m not going there next… 🙂
The answer is not what you’d expect I think. On a low use basis (for a car) the cyclist has about two thirds the impact of the wind car driver – better for sure but not exactly as massive a difference as you might have assumed. But on a car use scenario the wind car wins by a bigger margin – the cyclist has almost double the impact of the wind car.
The reason, I’m sure, is that human bodies are not anywhere near as efficient as electric motors – which are some of the most efficient machines we make. Our talents lie not in doing the work of machines but elsewhere… 🙂
PS – Here’s a thought – If wind powered cars were made using wind energy rather than fossil fuels (more than feasible in the near future), we could slash the embedded carbon figure for a wind EV by a couple of tonnes perhaps… and it would beat the bike in either mileage scenario. Just a thought.