It may be that this is something that varies based on your situation, where it is much cheaper for most people, but for others it might be close. There's nuances that I didn't explore in the interest of length. The moral of the story may be that one should live closer to frequent destinations (eg work).
In terms of eating, your bike gets 600MPG.
Let's say my car gets 30mpg, gas costs $3/gal and my commute is 30 miles. If we just look at gas, it's costing $3 for my commute. I eat at least $3 of extra food while cycling. That's about the cost of one (non-ERE) high end "energy" bar.
Of course, the cost of a car isn't just gas. Per day, it's:
(rounded up to nearest $.50, with all costs amortized assuming operation only during weekdays; worth of car and bike are about the same, so I ignored that)
I'm ignoring many things, including:
I might have been lucky with car repairs.
My car is depreciating slower than my bike (for now).
I like cycling, so riding during my commute is "found" time.
So on raw numbers the bike probably edges the car out.
And maybe I missed something?
Weekly maintenance? My beater bike gets annual maintenance, if that.
Around here there's dirt roads. Every week I clean the chain, derailleurs, and brake surfaces to get the grit out. Without this, I go though transmissions quickly and the rims get scored. Once a month I quiet the water induced squeaks and groans with some lube.
Special bike shorts: $20.
I think this is pretty much right.
Flats: That's what Mr Tuffy is for.
But not all flats come from punctures. I use puncture proof tires, but I still have valves go on me or get snakebite once or twice a season.
Special situations: Rental cars, taxis, uhaul/home depot trucks (or if you're hardcore, you get a serious bike trailer).
Yes for rentals, although they may not be convenient.
In rural areas, there may be no taxi service. If you need transportation quickly, you might be able to rely on neighbors, but many of them are working during the day.
I did a calculation in the ERE book and your biggest expense is opportunity cost which depends on the distance.
Section 6.5? But this was based on a three mile trip in what seems like a non-beater (20% of salary) car, presumably in a city since it includes parking and traffic lights.
I ignored opportunity costs, since I'd bike anyway. :)
I usually don't use a beater bike for my commute. I think a three mile city trip on a beater is a different situation. Worst case breakdown, you'll have to hike-a-bike 1.5mi on sidewalks. Even during winter, that's not bad.