What is the definition of 'grade' in highway terms?

In highway terminology, 'grade' refers specifically to the slope or incline of the roadway surface. It describes how steep the road is, which is crucial for factors such as water drainage, vehicle performance, and safety. A positive grade indicates an upward slope, while a negative grade shows a downward slope.

Understanding grade is vital for construction and design, as it affects vehicle speed, control, and braking distances. Properly managing grade can help mitigate issues such as hydroplaning and accidents.

Other options do not fit with the correct definition of 'grade' in this context. For instance, the pH level of soil is not related to the slope of a roadway, nor is it a direct factor in highway design. Likewise, the height of the road above sea level focuses more on elevation rather than the angle or slope of the road. The measurement of traffic capacity pertains to how many vehicles can effectively use a roadway and does not address the incline aspect critical to understanding grade.