What is "keying" in highway construction?

Answer: A — method of connecting different pavement layers.

Keying in highway construction refers to a method of connecting different pavement layers. This technique involves creating a groove or notch in the surface of a layer of material, such as asphalt or concrete, which helps to interlock the layers. This connection is crucial for ensuring that the layers behave as one cohesive unit, which enhances the overall structural integrity and performance of the pavement. Properly keyed layers can help resist lateral movement, provide better load transfer, and improve the durability of the roadway. The other options focus on different aspects of highway construction. Measuring road slope is important for drainage and safety, designing traffic signals involves separate criteria related to traffic management, while soil stabilization refers to processes used to improve soil properties for construction purposes. These aspects, while critical in their own right, do not specifically pertain to the concept of keying as it relates to the interconnection of pavement layers.