In terms of road safety, what is one of the main functions of solid lines?

Solid lines on the road serve a crucial role in indicating no passing zones to vehicles. This means that when you see a solid line on your side of the road, it is a visual cue that overtaking another vehicle is not permitted in that area. The presence of a solid line helps to enhance safety by clearly communicating to drivers that they need to remain in their lane. It is particularly important in areas where visibility is limited or where it may be dangerous to change lanes or pass another vehicle, such as on hills, curves, or approaching intersections. This regulation helps to reduce the risk of collisions that can occur when drivers attempt to pass where it is not safe to do so.

The other options do not pertain directly to the primary function of solid lines. Solid lines do not indicate walking paths or determine speed limits; those functions are addressed through other road markings or signage. While they can indirectly benefit cyclists by maintaining lane integrity, guiding cyclists is not the main purpose of a solid line. Hence, the main function of solid lines is indeed to signal to vehicles that they should not pass in those zones, making the road safer for all users.