Book 25, Question 29
How do road builders make a road layer by layer?
A road starts with leveled, packed soil.
On top go layers of crushed stone that spread out the weight of traffic and let water drain away. Finally, workers lay hot asphalt or pour concrete on the top. The road is slightly higher in the middle, so rain runs off to the sides. Big machines like graders, pavers, and rollers do the work.