What’s a rumble device designed to do?

Rumble Devices

Rumble devices, or rumble strips, across the road, either in the form of strips or larger areas, provide a visual, audible and vibratory effect. The intention is to alert drivers to a hazard ahead, usually a bend or road junction, and encourage them to reduce speed. SABRE, the Society for All British and Irish Road Enthusiasts, has information on them.