I don't know about the rest of you, but I have certainly believed (at times, at least) that the scarcity of petroleum will increase to the point that it would even make petroleum-derived clothing too expensive, to say nothing of burning a couple gallons to drive to work in the morning.
My question is, what do you think is going to happen to roads if/when it becomes too expensive to pave a road with millions of gallons of petroleum every couple of decades? I could be wrong, but my guess is that the "bottom of the barrel" sticky part of crude oil in roads is going to run out around the same time as the lighter motor fuel part, and that cars will wear out the roads they run on somewhere around the same time they wear out the oil resource they, ummmm, run on.
Stone paving works okay for pedestrians, but it's pretty bad for your average bicycle. There are plant substances that have at least some of the characteristics that make asphalt (that black stuff) a desirable material for paving. But I really don't know whether they'd ever be a workable alternative in terms of how much one can produce, how cheaply, and how well the stuff would work as an asphalt substitute.
Recognizing that almost all of us ride our bicycles around on millions of gallons of sticky black stuff from out of the ground, what do you think the road situation will be 100 years from now?