Final answer:
The road mender saw an untraveled road bordered by trees and no signs of human habitation. From this, we can predict that he will encounter a strange and isolated environment.
Step-by-step explanation:
The unusual sight that the road mender saw was a road that was wide and straight like a city street, but it seemed untraveled with no fields or dwellings nearby. The road was bordered by black bodies of trees forming a straight wall on both sides. From this, we can predict that the road mender will encounter a strange and isolated environment on his journey.