What type of line is used as a left edge line on divided highways?

A single solid line is used as a left edge line on divided highways to signify the boundary between the travel lane and the shoulder or the edge of the roadway. This solid line indicates that drivers should not cross over it, as it marks the limits of the driving area. It helps maintain safety by providing a clear visual cue that delineates the lanes of traffic, ensuring that vehicles stay within their designated paths. This is essential in preventing accidents by keeping vehicles from unintentionally straying into oncoming traffic or off the roadway. The solid nature of the line is crucial; it conveys a definitive rule that crossing is not permitted, unlike dashed lines which might suggest that lane changes are allowed.