The disturbing propensity for post-apocalyptic stories to forget that bicycles exist.
In most of these films, there always seems to be a gap between having a vehicle and gas and being shit out of luck, as if no other possibility existed.So somebody dropped the nuke. Maybe the zombies showed up and ruined society. Or it was the aliens and their battle lasers. But somehow, you're stuck in a crapsack post-apocalyptic world, and you need to stay on the move. You hear that there's some nice little place to hole up in somewhere in Maine, and you jump in your car to drive there. What's this? You're almost out of gasoline, and nobody owns a gas station any more? Well, you'd better hope that you used to own a horse ranch, because otherwise you're walking. After all, bicycles never seem to stick around for Ragnarok. This odd anomaly in transportation availability seems to manifest in many stories where it logically shouldn't. Sure, of course Frodo can't mountainbike his way into Mordor, and his pal Aragorn can't grab a BMX to reach Gondor with some fancy wheelies. But that doesn't stop Viggo Mortensen from somehow forgetting that bikes exist in The Road. Whether you're watching 28 Days Later or Mad Max, the problem remains. Fantasy and Sci-fi works involving post-apocalyptic worlds all have selective amnesia when it comes to the world-changing invention of the bicycle. Maybe it's because horses are just cooler than bikes, or maybe it's because all the idiots in the plot don't know how to pedal, or maybe it's because those world-destroying nanobots have a specific affinity for aluminum frames. At some point, the fridge logic sets in and viewers start wondering just what's wrong with post-apocalyptic humanity for them to completely ignore the world's most popular form of mechanical transportation. Now, if the ancient technology is randomly picked at and put together improperly, you've got yourself a Scavenger World, and it might at least make a bit of sense not to have too many bikes. That's at least a bit excusable. But if you're watching or reading a story where gas-powered vehicles exist and foot-powered ones mysteriously don't, then there are No Bikes In The Apocalypse. Compare Schizo Tech and Scavenger World. Contrast Ragnarok-Proofing, for those rare cases where bicycles are still around and in working order, 500 years after the fact.
I've already actually indexed the trope because I didn't realize that this process existed in such a capacity. http://tvtropes.org/pmwiki/pmwiki.php/Main/NoBikesInTheApocalypse Obviously, it needs more examples. I put a few of the more popular ones in there when I was writing the details. Gogo, Wiki Magic!