What does "subbase" serve in highway construction?

In highway construction, the subbase layer plays a critical role in providing support and stability beneath the pavement layers. This layer is typically composed of granular materials and is placed directly on the subgrade, serving as a foundation that distributes the load from the pavement above to the soil below. By effectively spreading the stresses imposed by traffic loads, the subbase prevents excessive deformation and helps maintain the structural integrity of the roadway over time.

This stability is crucial for the longevity of the pavement, as it directly influences the performance of the entire road structure, enabling it to withstand various environmental conditions and traffic stresses. The subbase's ability to support the weight of vehicles while minimizing the risk of settlement or failure makes it an integral component in highway design and construction.