Which type of testing is essential before the construction of a new highway according to IDOT?

Soil and geological testing is crucial before the construction of a new highway because it provides vital information about the ground conditions that will impact the design and construction of the roadway. Understanding the soil type, strength, and stability helps engineers determine the appropriate materials and methods for construction, ensuring the highway will be safe, durable, and capable of supporting expected traffic loads over time.

This type of testing can identify potential issues such as weak or unstable soils that may require special foundational actions, drainage solutions to prevent water accumulation, or changes in design to accommodate the characteristics of the land. Accurate geological assessments also help in predicting how the environment may affect the highway's lifespan and maintenance needs.

While water quality, air quality, and traffic density testing can play important roles in broader project considerations, they serve different purposes. Water quality testing is essential for environmental protection, air quality testing is related to public health and environmental impact assessments, and traffic density testing informs planning and operational considerations for the flow of vehicles once the highway is in use. However, none of these tests directly impact the structural integrity and foundational design required before actual construction begins.