Which condition is necessary for the right-of-way on a through highway?

The necessity for entering vehicles to yield to traffic already on the highway is rooted in the fundamental principles of traffic management and safety. When a vehicle approaches a through highway, it encounters a roadway designed for uninterrupted travel. This means that vehicles on the through highway have the right-of-way because they are already in motion and are not required to stop or slow down for entering vehicles.

Yielding ensures that the flow of traffic on the highway remains smooth and prevents collisions, especially since vehicles on the highway might be traveling at higher speeds. This yields not only contributes to safer driving conditions for both the drivers on the highway and those entering it but also helps to minimize traffic congestion.

In contrast, other conditions listed, such as requiring vehicles to be traveling in the opposite direction, mandating that all vehicles stop before entering, or that traffic signals are required at all entrances, do not reflect the established rules of right-of-way for through highways. These conditions would disrupt the intended efficiency and safety that comes from the current standard of yielding for entering vehicles.