What is the recommended distance to place warning devices on a two-way or undivided highway?

The correct answer identifies a specific distance for placing warning devices that helps ensure safety and visibility on a two-way or undivided highway. By positioning one device 100 feet behind the hazard (like a stopped vehicle or construction zone) and another 10 feet behind, you maximize the warning to approaching drivers well in advance of the danger while also ensuring there's a clear indication of what to expect closer to the obstacle.

This arrangement provides ample time for motorists to react and navigate accordingly, which is critical in maintaining traffic safety. The placement of warning devices at this distance creates a gradual ramp-up of awareness for drivers, as they’ll see the first device from a significant distance away and the second device as they approach closer to the situation.

In comparison to the other options, the distances or number of devices described would either not provide sufficient warning or would not adhere to safety standards typically recommended for effective hazard signaling on highways. For example, placing devices only 10 feet ahead may not give enough stopping distance, while just relying on two devices 200 feet behind might not account for varied speed limits and driving conditions that drivers could encounter.