What is the correct top-to-bottom order of the three runway layers?

What is the correct top-to-bottom order of the three runway layers?

• A. Surface Course; Base Course; Sub-base Course
• B. Base Course; Surface Course; Sub-base Course
• C. Sub-base Course; Base Course; Surface Course
• D. Surface Course; Sub-base Course; Base Course

Answer: (A)

The key idea is how pavement layers are arranged by function from the surface down. The topmost layer is the Surface Course, designed to resist traffic wear and weather. Beneath it sits the Base Course, which provides the main structural support and distributes loads deeper into the pavement system. The lowest layer among these three is the Sub-base Course, which enhances drainage, frost protection, and load distribution before the load reaches the subgrade. So the correct top-to-bottom sequence is Surface Course, then Base Course, then Sub-base Course. Placing the Base above the Surface or the Sub-base directly under the Surface would undermine wear resistance and drainage, reducing pavement performance.

The key idea is how pavement layers are arranged by function from the surface down. The topmost layer is the Surface Course, designed to resist traffic wear and weather. Beneath it sits the Base Course, which provides the main structural support and distributes loads deeper into the pavement system. The lowest layer among these three is the Sub-base Course, which enhances drainage, frost protection, and load distribution before the load reaches the subgrade. So the correct top-to-bottom sequence is Surface Course, then Base Course, then Sub-base Course. Placing the Base above the Surface or the Sub-base directly under the Surface would undermine wear resistance and drainage, reducing pavement performance.