What does a solid white line represent?

A solid white line is used to mark the right edge of the roadway, which provides important guidance to drivers. This line helps to delineate the boundary between the travel lane and the shoulder or the side of the road, enhancing safety by indicating where drivers should stay within their lane. It is particularly useful during low visibility conditions, such as at night or in bad weather, as it helps maintain awareness of the road's edge.

In contrast, the other options address different roadway markings or concepts. For instance, lane changes are generally not allowed with a solid white line, speed limits are indicated by signage, and traffic moving in opposite directions is separated by different markings, usually a solid yellow line. Understanding the function of solid white lines is crucial for safe driving practices.