I’ve wondered about this for years. I know bicycles are fairly efficient, but I wasn’t sure how efficient the human engine was. This takes all that into account.
It’s never a fair comparison, as much has to do with trip distance, speed, convenience etc. but it’s a fairly thorough review.
Using a bicycle, one can travel about 25 times as far on a Calorie of food than on a Calorie of gasoline (by automobile). Unfortunately, it took perhaps 15 Calories of fuel to create that Calorie of food, so the bicycle is only about 5/3 as energy-efficient per person-mile of travel if one doesn’t count the energy cost of the extra time it takes to travel by bicycle.
It takes about 15 times more mechanical energy to transport one by auto as compared to a bicycle. Even though automobile engines are at best about 50% more efficient than a human bicyclist pedalling, the bicyclist is typically about 2/3 more efficient than the auto engine in converting food/fuel into useful work, due to the failure of autos to fully utilize their higher efficiency. So considering only the mechanical and engine efficiencies (including the human “engine”) the bicycle is about 25 times more energy-efficient. But the high fossil fuel energy cost of making food reduces the 25-times advantage to less than 2-times. Counting the energy cost of the additional time it takes to get somewhere by bicycle may result in the overall energy-efficiency of the bicycle being worse than the auto
A bicycle does save energy in many cases, since it limits the distance people can travel and some (or all) of the energy used for bicycling might be used anyway for the exercise needed for health. To make it many times more more energy efficient (before counting the energy cost of time) requires greatly reducing the energy required to create and transport food. See Better Energy-Efficiency in Food Production