Roadway Design is More Than What Meets the Eye

I recently had the opportunity to talk about my job as an Infrastructure Designer with a young member of my church. They had a lot of questions about the roadway design process, such as “do you guys just put dirt down and call it a day?” The simple answer is this: roadway design is a lot more than what meets the eye.

Pavement Structures

When building a roadway, the first step is planning. This process may involve engineers, construction experts, and public input from town hall meetings. Items such as road location, construction materials to use, and the amount of traffic are all taken into consideration during the grading and alignment design.

After the design process, the next step is to determine the pavement structure. Designing a roadway requires many sub layers of pavement structures. This process of grading and compaction, also known as “Earthwork,” is the early construction phase of a roadway that utilizes large machinery to create the road’s solid foundation. This step is integral to the longevity of a roadway because an unstable road foundation can cause issues such as cracks and potholes: which are often expensive and time-consuming to repair.

Did you know that Sain’s founder, Charles “Hack” Sain, is the author of “Earthwork,” – Chapter 13 of Merritt’s Standard Handbook for Civil Engineers? This handbook is an essential manual covering the important principles and techniques used by civil engineers. Some other topics included in the book are construction materials, safety and health concerns, and structural theory.

Pavement structures can be split into two categories: rigid pavements and flexible pavements.

Rigid pavements include a subbase that provides permanent support, a stable foundation, and a pavement slab. Some materials used to construct the pavement slab layer are Portland cement concrete, reinforcing steel, and joint sealing materials.

Flexible pavements include a prepared roadbed, subbase course, base course, and surface course. A prepared roadbed is the natural soil at the bottom of the roadbed compacted to the state DOT’s standards. The next layer, a subbase course, consists of granular material that is compacted. The subbase course may be treated or untreated and is generally used to provide stability over poor roadbed soils. The base course is constructed from crushed aggregate or Hot Mix Asphalts (HMA). This layer provides load distribution from traffic. Finally, the surface course layer is the top layer that meets the traffic. The surface course can be subdivided into the wearing surface (the surface traffic is in contact with) and the binder course (that binds the surface course to the base course).

Other design considerations include:

  1. Pavement performance
  2. Traffic
  3. Roadbed soil
  4. Materials of construction
  5. Environment
  6. Drainage
  7. Reliability
  8. Life-cycle costs
  9. Shoulder design

Designing a proper foundation for a road is essential to creating a roadway that is smooth for drivers and meets safety requirements. We make sure the roads we build are designed in such a way that they can be used for many years to come. One of our recent roadway design projects was the Will Buechner Parkway in Auburn, Alabama.