"I have this new auto-mobile concept which doesn't require a horse and which can go fast; I envision up to fifty miles per hour. It will require a smooth, hardened road surface, but that will be achievable someday."

"Forget about it. We already have millions of miles of roads, which are bumpy, made of dirt, and hard to build and maintain. Who will do the extra work to smooth them? Harden them? Maintain them? What if some jerk digs a hole in one as a prank? Maybe this could happen in a limited way in cities, but this is overall a pipe dream."

My point is, it isn't a question of whether this is feasible, it's a question of incentives. If the incentives lead society in this direction, it will happen.