Same reason we have safety rails around roads. Plus, if we want solar roads, solar power would be a perk. I mean, once the road is dominated by self-driving c

Same reason we have safety rails around roads. Plus, if we want solar roads, solar power would be a perk. I mean, once the road is dominated by self-driving cars, presumably we can implement new driving requirements beyond what human drivers could implement. For roads, we might want cars to drive over load-bearing parts, if that's optimal. Or if it's more efficient to have the wear-and-tear distributed, then cars can drive in staggered formations, much like a wear-leveling strategy in solid-state drives (SSD's). But, there's no reason to design a transportation system around the premise that self-driving cars can't control their patterns just because human-driven cars couldn't. Which isn't to say that we should assume that self-driving cars will be perfect or infallible, just that we can assume best-effort strategies. For example, we shouldn't assume that self-driving cars would never drive over a gap with a solar panel, but we can design a system in which self-driving cars try to avoid driving over the solar panels.