What does a solid white line indicate on the road?

A solid white line on the road serves to indicate that lane changes are discouraged and should be made only when necessary. This means that while it is technically possible to cross this line, drivers are expected to stay in their lane unless a valid reason exists, such as avoiding a hazard or turning into a driveway. The presence of a solid white line helps promote safety by reducing erratic lane changes and encouraging drivers to maintain their position in traffic. The line visually reinforces that the lanes are intended to be clear and orderly, minimizing confusion on the road.

Choices regarding lane changes being freely allowed or passing being permitted are incorrect because those scenarios generally require broken lines, which signal a different set of rules. Lastly, while a solid white line may mark the edge of the roadway in some contexts, its primary function in a lane context is to regulate lane usage more than to define the road's edge.