Walking pollution: ...

That's right, bike pollution is less than walking (or running) pollution in terms of CO2 per mile travelled. Cycling typically burns ~⅓ of the calories compared to making the same journey on foot and there's a direct link between calories burnt and CO2 produced.

Cycling at 12mph takes roughly the same energy as walking at 4mph. You emit the same CO2 per minute, but get there in ⅓ of the time. Running at 12mph takes 3 times the effort of cycling at 12mph. You'll get there in the same amount of time, but breath out 3 times as much CO2. Bicycles are more efficient than our own two legs - how cool is that!