And a bike doesn't need a road 2-rod wide. Just a path as wide as a bike tire. Even a good shoulder. And cement roads can last far longer than asphalt. Definitely situational.
Anywhere a car could go, a bike could go further I think.
The road in question was closed as a result of a 1983 earthquake. Part of the road is now used as the Crater Rim Trail, and if you pan around a little bit, you can see just how close the trail is to the current rim of the crater. I don't know how long ago those pictures were taken, but my recollection of the road's condition circa 2005 when I hiked the trail wasn't all that much better.
While the parts of the ex-road that are now used as a trail are in decent enough condition, the parts that are not are not in any condition to be used as a path. Admittedly, this is the windward side of Hawaii (and hence very conducive to fast growth), but the usable lifespan of an unused, unmaintained asphalt road should generally be figured in the region of a few decades at most.
Doesn't it run from energy generated by the Hoover dam?
Without it, in a fast unplanned event at least, humanity would face a very big population reduction.
Yes, but I don't think they're doing much of that in the immediate area around Las Vegas (which is what the parents of my original comment were discussing).
South of the Mason Dixon line roads require annual landscaping to prevent overgrowth.
Much like technology is spread very unevenly, post-apocalyptic is spread very unevenly. There is a large subculture of urban explorers on youtube, interesting stuff to watch. Interesting to see them explore sites abandoned around the turn of the century, driveways / roads and such are essentially impassible.
There are exceptions. Youtube abandoned mine explorers visit sites abandoned a century ago out west and other than the occasional landslide desert roads can remain clear for a century or so. Of course without massive fossil fuel burning, Vegas can't exist, so great roads aren't very useful without any population to travel them... Similar problem with the deep south USA, before air conditioning the number of people living down there was low.