CABI Blog

This blog is a continuation of my last blog on eco questions. I thought I would tackle 3 transport questions today.

Does switching from bus to bike have a real effect on the environment? Especially when considering cyclists are not totally carbon neutral, as they need to eat to fuel their legs.

You are much better off cycling. A 12 km round commuting trip on a bus or subway train is estimated to generate 164 Kg of carbon per commuter per year. A person cycling the same distance would burn about 50000 calories a year, which is roughly the amount of energy in 22 Kg of brown bread. A Kg of brown bread has a carbon footprint of around 1.1 Kg. Therefore switching from public transport to cycling will save about 140 Kg of carbon emission per year. However, this only works if enough people cycle so that the number of public transport vehicles on the roads would also be reduced.

What is the most fuel-efficient way to drive?

• Do it smoothly. Avoid sudden braking (ignore this advice in an emergency, emergency braking is allowed) and acceleration and use cruise control if you have it.
• Move through the gears as quickly as possible, i.e. change up before you hit 2500 rpm (2000 rpm for diesel vehicles).
• Whenever possible drive at a steady 55 miles per hour (90 km/h). It is up to 20% more fuel efficient to drive at a steady 55 miles/h than at 75 miles/h.
• Check your tyre pressure once a month, as an under-inflated tyre can increase fuel consumption by as much as 6%.
• Don't carry unnecessary excess baggage, as each 25 Kg decreases fuel consumption by 1%.
• Avoid short trips, as a cold engine uses twice as much fuel as a warm one.

Is a full commercial plane more fuel-efficient over long distances than a car?

Not if the car is also full. Consider this: Easyjet, which claims to be 30% more fuel efficient than other carriers, mainly because it packs in more people, calculates that on an average flight each passenger accounts for 95.7 g CO₂ per Km, compared to 164 g for someone travelling by car. On average their flights are 80% full, which means that figure would fall to 76 g CO₂ per passenger, if every seat in the plane was taken. The figure for a fully-occupied (4 passengers) car is 41 g CO₂ per passenger per Km. A full long haul flight (more than 4000 Km) would be more efficient than Easyjet, since short or medium haul are 1/3 less efficient than long haul. The figure for long haul would be 50 g CO₂ per passenger. Therefore, cars win no matter what the distance. However, planes are obviously more appropriate when we have to cross over the oceans.

Source: New Scientist No. 2682, vol 200, Nov 2008.