Based on past Derry Township Program Management Meetings, the Township requested guidelines for the placement of speed humps as a traffic calming measure within the Township. As such, HRG gathered general guidelines for the applicability and placement of such speed humps.

TYPES OF SPEED HUMPS

WATTS SPEED HUMP

Watts speed humps are the most common in Pennsylvania, typically 3-4 inches in height, 12 feet in length, and generally span the entire width of the roadway (though they can taper at the edge of curbed sections to facilitate drainage).

  • Watts speed humps generally slow vehicles to 15-20 mph at each hump and 25-30 mph in between properly spaced speed humps.
  • Watts humps typically delay emergency vehicles between 3 and 7 seconds.
  • Traffic may divert onto other parallel streets that do not have traffic calming measures.

SEMINOLE COUNTY SPEED TABLE

Seminole County speed tables may be a suitable alternative to a Watts speed hump. They are larger with less vertical displacement – typically 3” in height and 22’ in length, with a 10’ flat area across the top.

  • Seminole County speed tables generally slow vehicles to 25-30 mph at each hump and 35 mph in between properly spaced speed humps.
  • Seminole County speed tables typically delay emergency vehicles by only 1 second.
  • Seminole County speed tables are generally more suitable along emergency response routes or higher-volume roadways.

SPEED BUMPS

Speed humps and tables are different than speed bumps (often encountered in parking lots). Speed bumps are usually 3 to 6 inches in height and 1 to 3 feet in length, forcing traffic to slow to 5 to 10 mph. Speed bumps cause severe vertical displacement even at low speeds and should not be used for traffic calming along public roadways.

NEGATIVE IMPACTS OF SPEED HUMPS

Speed humps have a well-documented history of slowing traffic along public roadways. However, speed humps can also have negative impacts to the community so other treatments should be first considered. Such negative impacts of speed humps include:

  • Noise
  • Driver Discomfort
  • Bicycle Discomfort
  • EMS
  • Snow Removal
  • Installation Cost
  • Maintenance Cost
  • Environmental – fuel, air pollution
  • Wear/tear on brakes, suspension
  • Difficult to remove – cost and public perception/liability
  • Drainage
  • Drivers avoid – other routes and/or drive off-road

SPEED HUMP/TABLE PLACEMENT – RECOMMENDED PRACTICE FOR DERRY TOWNSHIP

  • Upon request for speed humps, the Township should consider alternate traffic calming treatments before electing to install a speed. Such measures may include targeted enforcement, improved signing, or other measures as identified in PennDOT’s Traffic Calming Handbook. If other measures are impractical or ineffective, speed humps may be further considered.
  • For consideration of speed humps or tables, roadways should have an average daily traffic (ADT) of at least 1,000 vehicles per day.
  • Speeds humps/tables should be considered when the 85th percentile speed exceeds the posted speed limit by at least 10 mph.
  • Prior to installing speed humps in residential areas, a door-to-door inquiry of property owners should be conducted to confirm support for the treatment. A 60% approval percentage is recommended.
  • Speed humps/tables should not be placed within 150 feet of an unsignalized intersection nor 250 feet of a signalized intersection (further if intersection queues dictate).
  • Speed humps/tables should not be placed on curves with a radius less than 300 feet.
  • Speed humps/tables should not be placed on roadways with grades greater than 8%.
  • Speed humps/tables should be spaced approximately 500 feet apart.
  • It is desirable to install speed humps/tables on curbed roadways, though they could be installed on uncurbed roadways if physical obstructions exist (delineator posts, signs,) to prevent vehicles from driving around them.
  • Consideration should be given to whether traffic may divert to other parallel roadways.
  • A speed hump warning sign (W17-1), speed plaque (W13-1P) and associated pavement markings should be installed at the speed hump/table.
  • Watts speed humps may be installed on local streets with an ADT less than 3,500 vehicles per day.
  • Watts speed humps should be installed on roads with a posted speed limit of 30 mph or less.
  • Seminole County speed tables may be installed on collector roads and/or roads with an ADT between 3,500 and 6,500 ADT.
  • Install Seminole County speed tables along major emergency service routes.