Something I've noticed* while passenging on many not-very-recently-paved roads, especially those outside of cities, is that, after a dip or bump in the road, there is often a diffuse dark patch on the road.
This, I believe, is the result of oil drops being triggered to fall from vehicles. If the oil
is leaking slowly, a drip will form somewhere on the underside of the vehicle. Normally, on a flat road, such drips will fall off with a uniform distribution along the length of the road, as enough leaks out to break off under its own weight, over and over. However, if there's a dip or a bump, that jostling will cause the drip to drop before it would otherwise be ready to. This leads to a larger amount of oil landing on the road immediately after any bump or dip, causing a dark patch.
These dark patches could be detected with a sufficiently resolute aerial or satellite survey, to be used for road maintenance planning. The characteristics of the dark patches could also be analyzed to determine the severity of the dip or bump.
N/A [many years ago]
*Though, recently, I've also noticed the conspicuous absence of this phenomenon, on roads that look old enough to display it.