What is the definition of 'rutting' when discussing pavement surfaces?

Rutting is defined as the permanent deformation that occurs in the wheel paths of a pavement surface, primarily as a result of repeated traffic loading. This phenomenon arises when the material in the pavement structure is unable to withstand the stresses imposed by vehicle tires, leading to a gradual sinking or shaping of the surface in the areas where the vehicles frequently travel.

The correct answer accurately captures the essence of rutting, highlighting that it is a lasting change in the pavement profile that impacts road safety and performance. Excessive rutting can lead to water pooling, increased hydroplaning risks, and can significantly affect the ride quality and structural integrity of the highway.

In comparison, the other options do not correctly define rutting. Surface cracking due to temperature changes refers to thermal cracking, which is different from permanent deformation. Displacement of pavement layers due to moisture relates to issues such as stripping or loss of bond, but does not specifically address the concept of rutting caused by traffic. Similar, the formation of potholes involves structural failure of the surface due to a variety of factors, but does not relate directly to the concept of rut formation seen under constant traffic loads.