Book 25, Question 30
Why are some roads black and some light gray?
Black roads are made from asphalt, which is a sticky black material from oil mixed with stones.
It is quick to lay, bendy, and quiet to drive on. Light gray roads are made of concrete, a mix of cement, sand, and gravel. Concrete is hard and long-lasting but can crack and thump at joints. Each is chosen to fit the job, climate, and cost.