Cycling is about 31 Calories/Km (for a pretty average person)
To compare this to driving we need to do a little more leg work:
First we need the Caloric value of gas (we'll figure it out for a Liter of gas):
((MJ/Kg of gas) * (convert to Jules) * Kg per Liter of gas) / (J in a Calorie) = Calories/Liters of gas
(44.374 * 1000000 * .703) / 4184 = 7455.76 C/L of gas
Now we take this number and plug it in to the efficiency of a car:
Efficient car (40mpg) in Km/L : 17.01 km/L
(Calories in a Liter of gas) / (Km/L of an efficient car =
7455.76 / 17.01 = 438.31 Calories/Km for an efficient car
Therefore with these rough numbers Biking is around 14x more efficient then driving. And yes I know measuring gas in calories doesn't really make much sense... but it does help when making this sort of comparison.
Interesting side notes:
- You burn about a McDonald's double cheeseburger of calories every Km you drive.
- You burn around half an apple of calories ever Km you bike.
Where I got my numbers:
- Calories in a big mac: http://caloriecount.about.com/calor
- MJ/Kg of gas: http://stason.org/TULARC/vehicles/gasol
- Liters in a Kg for gas: http://www.triplepundit.com/pages/askpa
- Calories/Km of for biking: http://www.stevenscreek.com/goodies/cal
- Calories in a Cheese burger: http://caloriecount.about.com/calor
- Calories in an Apple: http://caloriecount.about.com/calor