What is the purpose of shoulder rumble strips on roadways?

Answer: B — To alert drowsy drivers through vibration

Shoulder rumble strips are primarily designed to alert drowsy or inattentive drivers when their vehicle drifts too close to the edge of the roadway. When a vehicle travels over these strips, they create a tactile and audible vibration that can wake up a sleepy driver or refocus their attention on the road. This feature is vital for preventing accidents that can occur due to drivers unknowingly leaving their lane, particularly in high-risk areas or on highways. The other options do not accurately reflect the function of shoulder rumble strips. For instance, they do not indicate speed limits, provide tire grip, or signal upcoming exits. Their main and vital role is to enhance safety by helping to prevent unintended departures from the roadway.