>>12842294This is a good failure mode for road surfaces to have. The depth of those ruts shows that even after the ruts began, wagons still found the roads passable (and thus continued to wear the ruts even deeper.) For centuries, wagons continued to use those roads, wearing those ruts deeper.
However when a modern road starts to fail, the failure is usually a run-away process; water gets under the asphalt and causes a small void. That void is then filled with water during subsequent rainstorms, and each time the water drains away it carries away more dirt leaving a larger void. Eventually the asphault collapses into that void, forming a 'pothole', at which point erosion of the earth beneath the road accelerates. A modern road built like this will deteriorate in mere decades even if no cars drive on it at all. Similar happens with ice and concrete roads. Once any ice gets in and starts a crack, that crack will later accommodate even more water freezing causing an even bigger crack. The decay of a concrete road in icy climates accelerates over time, even if the road is unused.
Roman roads tolerate both of these well. Their layered construction was designed to let water drain through the road without eroding away the material supporting the road, alleviating the pothole problem. Asphalt roads COULD use layered constructions like this, and generally do to some limited degree, but they do the bare minimum to keep the road working for a few years. As for ice, a roman road tolerarates freeze/thaw cycles fairly well because it has a segmented construction. Ice gets into the cracks between the rocks and pushes them outwards, but for the most part the ice isn't getting into the rocks themselves and isn't breaking up the rocks, only moving them around a little. When the ice thaws the rocks settle back into place. Over time this can move rocks around and degrade a road, but the damage is not nearly so extreme as that which a concrete road suffers.
