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traffic calming collage

David Engwicht on Speed Humps

"... you’ve got traffic braking to go -- bump, bump -- over the speed bump and then speeding up between ..."

“Speed bumps aren’t the panacea that a lot of people think they are because …. somebody has to put up with the noise of people going over them outside their house and, interestingly enough, the people between the speed bumps have to put up with faster traffic. The traffic speeds up to make up the lost time from slowing down. Instead of an even pace in the street, you’ve got traffic braking to go -- bump, bump -- over the speed bump and then speeding up between (them)”.

Source: David Engwicht, best-selling international author on traffic calming, at “Mental Speed Bumps” lecture given in Vancouver, Washington on October 19, 2005. (Filmed by CVTV, who provided videotape.)

Engineering research backing up David Engwicht's observations

Example 1 - Intention

"When designed and installed properly, speed humps will reduce vehicle speeds to 15-20 mph at the hump and 25-30 mph between humps in a series."

Source: "A Study on Speed Humps" prepared by the Center for Transportation Research and Education at Iowa State University, Duane E. Smith, P.E. and Karen L. Giese, September 1997

Example 2 - Comparison of Speeds "On Humps" and "Between Humps"

Speed Hump Location Design Type Speed on Speed Humps Speed between Speed Humps
1 Av NE Seminole
29 MPH
36 MPH
Freemont Av N Watts
24 MPH
29 MPH

Source: Mid-Block Speed Control: Chicanes and Speed Humps, John C. Marek and Shauna Walgren, Seattle Transportation

Example 3a - Resulting Increase in Pollution

"Speed humps cause atmospheric pollution from the speeding up and slowing down of traffic between the humps (see TRL report No. 482 on this subject). For example, TRL reports a 59% increase in CO, about 50% increase in HC and about 25% in CO2 from petrol catalyst vehicles averaged over all types of traffic calming measures, with even higher numbers over more "severe" measures such as speed humps."

Source: The Objections to Speed Humps (Submission to the London Assembly)
Published by the Bromley Borough Roads Action Group (B.B.R.A.G.), October 2003

Example 3b - TRL Report 482 (2001)

TRL Report 482 / 2001 “The Impacts of Traffic Calming Measures on Vehicle Exhaust Emissions”, Boulter, P.G., Hickman, A.J., Latham, S., Layfield, R., Davison., P. (AEA Technology), Whiteman, P. (AEA Technology), 2001 - available from Transport Research Laboratory (£50.00)

Reviewed -

"For these newer vehicles some modes of operation, such as rapid accelerations (which may occur on some roads with traffic calming), can result in fuelling conditions which deviate from those required for the optimum control of pollutants. Any such deviation can result in a momentary emission rate that is an order of magnitude higher than the baseline rate."

Source: "Traffic calming pushes up emissions", Air Quality Management, Issue Nbr. 64, April 2001

Example 4-a - Noise at Speed Hump in Addition to the Noise from Braking and Accelerating

"Speed bumps increase noise levels 10 to 20 decibels when wheels hit the bump. This increase in noise can be bothersome in quiet residential neighborhoods."

Source: City of Livermore, California, (website, November 2005)

Example 4-b - Residents Complained about Increased Noise Level in Omaha Study

"In Omaha, Nebraska, ... residents complained about the speeding that still existed, as well as about vehicle damage and increased noise levels."

Source: "Effects of Traffic Calming Measures on Pedestrian and Motorist Behavior", Herman F. Huang and Michael J. Cynecki, Transportation Research Record 1705, Paper No. 00-0443

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