If a solid white line on the right edge of the highway slants in to the left, it shows that:

When a solid white line on the right edge of the highway slants inward to the left, it indicates that the road is narrowing. This signaling is important for drivers as it prepares them for a change in the roadway width, allowing them to adjust their speed and position accordingly. A narrowing road can present challenges such as reduced lane space and increased potential for collisions if drivers are not aware of the change. Recognizing and heeding this visual cue is essential for safe driving and navigation.