Sure. This paper in Nature, estimates walking and cycling to generate 0.26 and 0.14kg CO2, respectively, given the diet in the most economically developed areas (I noted "typical western", not world wide or average) in my post). The EPA calculates gasoline at 8887g CO2 per gallon, so a car which gets 39mpg (note I mentioned fuel efficient - not average) is around 0.14 kg CO2 per km (8887/39mpg/1.628km) and a car which gets 21 MPG is around 0.26 kg CO2/km (which actually is close to the average vehicle).
Nature bases their estimates on full-replacement calories for the energy burned. YkmMV based on style, location, traffic, weather, and a bunch of other factors. Walking and biking is healthier for you and will likely extend your life and increase your resting metabolic rate (=the CO2 you create just lying about), but I'm not counting that against the walkers/bikers in this equation ;-)
Note: I walk quite a bit for fun - logged about 250km on my vacation last fall - and I bike when the weather is nice - often not even to go anywhere I need to; I'm just adding to the carbon problem for personal health and entertainment purposes.