Rumble strips, also known as sleeper lines or audible lines, are a road safety feature that alert inattentive drivers to potential danger by causing a tactile vibration and audible rumbling, transmitted through the wheels into the car body. A rumble strip is usually either applied in the direction of travel along an edge - or centerline, to alert drivers when they drift from their lane, or in a series across the direction of travel, to warn drivers of a stop ahead or nearby danger spot. In favorable circumstances, rumble strips are effective (and cost-effective) at reducing accidents due to inattention.