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Traffic Calming Fact Sheets May 2018 Update Speed Cushion Description: • Two or more raised areas placed laterally across a roadway with gaps between raised areas • Height and length similar to a speed hump; spacing of gaps allow emergency vehicles to pass through at higher speeds • Often placed in a series (typically spaced 260 to 500 feet apart) • Sometimes called speed lump, speed slot, and speed pillow Applications: • Appropriate on local and collector streets • Appropriate at mid-block locations only • Not appropriate on grades greater than 8 percent (Source: James Barrera, Horrocks, New Mexico) (Source: Delaware Department of Transportation) ITE/FHWA Traffic Calming EPrimer: https://safety.fhwa.dot.gov/speedmgt/traffic_calm.cfm Design/Installation Issues: • Two or more cushions at each location • Typically 12 to 14 feet in length and 7 feet in width • Cushion heights range between 3 and 4 inches, with trend toward 3 - 3 ½ inches maximum • Speed cushion shapes include parabolic, circular, and sinusoidal • Material can be asphalt or rubber • Often have associated signing (advance-warning sign before first cushion at each cushion) • Typically have pavement markings (zigzag, shark's tooth, chevron, zebra) • Some have speed advisories Potential Impacts: • Limited-to-no impact on non-emergency access • Speeds determined by height and spacing; speed reductions between cushions have been observed averaging 20 and 25 percent • Speeds typically increase by 0.5 mph midway between cushions for each 100 feet of separation • Studies indicate that average traffic volumes have reduced by 20 percent depending on alternative routes available • Average collision rates have been reduced by 13 percent on treated streets Emergency Response Issues: • Speed cushions have minimal impact on emergency response times, with less than a 1 second delay experienced by most emergency vehicles Typical Cost (2017 dollars): • Cost ranges between $3,000 and $4,000 for a set of rubber cushions