Final answer:
A vehicle towing a trailer keeps right on a highway because it moves slower than other vehicles, which is a safety measure to aid traffic flow and reduce congestion. The rightmost lane is intended for slower-moving traffic, allowing faster vehicles to pass on the left.
Step-by-step explanation:
On a highway with three lanes in each direction, it is often recommended that a vehicle towing a trailer keeps right because it moves slower than other vehicles. Slower moving vehicles should stay in the right-most lane, or the 'slow lane,' to allow faster-moving traffic to pass on the left. This also contributes to overall road safety and helps maintain traffic flow. The right lane is known as the traveling or truck lane, which is specifically meant to cater to vehicles that are not traveling at higher speeds.
While lack of visibility and the presence of a No-Zone may affect the operation and positioning of a vehicle on the road, these are not the primary reasons for slower vehicles to keep right. Typically, higher-speed lanes are located towards the center or left side of the road, while the rightmost lanes are used by vehicles that are entering or exiting the highway or those that are traveling at a slower pace, including those towing trailers.