A COMPARATIVE STUDY OF SPEED HUMPS, SPEED SLOTS AND SPEED CUSHIONS

Abstract. The primary objective of this study was to compare speed humps with two newer traffic calming devices that are gaining popularity in the US, the speed slot and speed cushion. Crossing speed and driver behavior were measured at selected traffic calming devices on roadways in the Washington DC metropolitan during the summer of 2003. The subject devices include: • 12-ft and 22-ft asphalt speed humps; • 14-ft prefabricated speed humps; • 22-ft speed slots; and • 10-ft speed cushions. All ranged from 2.5 to 4.0 inches in height. Video surveillance technology was used to collect data, including vehicle crossing speed, lateral placement and braking frequency. Preliminary results revealed that speed slots allowed the highest average and 85th percentile crossing speeds. Speed cushions, 12-ft speed humps and 14-ft prefabricated speed humps recorded the lowest crossing speed and relatively high frequency of braking maneuvers. The designs of the speed hump and speed cushion encouraged drivers to travel centrally within their lane. Lateral positioning while traversing the speed slot was varied; a large percentage of drivers attempted to place the vehicle’s left tires in the slot.