The following five case studies cover both (1) effective processes used to plan and define a local traffic calming program or project and (2) assessments of the effects of individual and series of traffic calming measures. A brief summary is provided for each case study, followed by a hyperlink to a report or other document that provides additional detail.
City of Wauwatosa (Wisconsin) Traffic Calming Case Study
The City of Wauwatosa, Wisconsin is located immediately west of Milwaukee and has a population of nearly 50,000. The traffic calming study area is a residential neighborhood through which vehicular traffic was thought to be cutting through in order to avoid traffic congestion on nearby streets. The neighborhood is served by three streets, each with a posted speed limit of 25 mph and a width of 30 feet with on-street parking.
Four measures were used to assess the degree of a traffic cut-through or speed problem on the study area neighborhood streets:
- A comparison of traffic volumes between parallel neighborhood streets (including an estimate of excess traffic not generated by the neighborhood dwelling units along with hypotheses for why volumes on one street differed from another)
- Identification of a peak hour percentage of daily traffic volume that was atypically high (i.e., as a likely result of diversion of traffic from congested nearby major streets)
- Measurement of 85th percentile and maximum vehicle speeds by direction (maximum speeds of 60 mph were measured on two of the streets)
- Field observations of (1) queuing on nearby major streets and (2) apparent cut-through turns at neighborhood street intersections with major streets at the neighborhood boundary
Four types of traffic calming measures were considered: speed hump, speed table, median island, and choker. The recommended action was to install speed tables on all three neighborhood streets – a pair of speed tables on two of the streets and a midblock speed table on the third street.
The full report can be accessed at the following hyperlink:
https://www.ayresassociates.com/project/traffic-calming-case-study/
City of Sunnyvale (California) Canary Drive Traffic Calming Case Study
The City of Sunnyvale, California is located in Santa Clara County near San Jose and has a population of approximately 140,000. The city has an established traffic calming policy. The following case study describes an application of the process for a specific neighborhood residential street. The case study covers the analysis of the problem, selection of an appropriate traffic calming action, implementation of the action, and evaluation of its effectiveness in resolving the observed problem.
The policy defines initial criteria that must be satisfied for any traffic calming measures to be considered.
- The road must be classified as a neighborhood residential street
- The ADT must be greater than 1,000 vehicles
- The 85th percentile speed must be greater than 32 miles per hour
Canary Drive is a neighborhood residential street with single-family homes. Its length is 1,200 feet and has a posted speed limit of 25 mph. Neighborhood residents reported concerns over high-speed traffic and unsafe driving on the street. The daily volume of 1,200 vehicles and 85th percentile speed of 35 mph met the threshold for consideration.
The policy defines a range of measures that can be considered once initial data collection is complete. The Stage I measures include education/neighborhood outreach, police enforcement, increased signing and striping, deployment of radar speed trailers, and warranted traffic control measures (Stop/Yield signs). With the support of the neighborhood, a subset of the Stage I measures were selected for implementation: additional speed limit signs, increased enforcement of the speed limit, deployment of a radar speed trailer, and installation of a double yellow centerline.
Four months after Stage I implementation, traffic volumes and speeds were reevaluated. Daily traffic volume had decreased from 1,200 to 1,100 and 85th percentile speed had decreased from 35 mph to 34 mph. The post-implementation volume and speed values still exceeded the initial threshold criteria.
Potential Stage II traffic calming measures were then evaluated. The measures include speed humps and tables, traffic circles and roundabouts, median islands, corner extensions and chokers, median barriers and median barriers, turn prohibition signs, and street closures. Technical analysis and neighborhood support settled on three measures: a median island, speed hump, and traffic circle.
A temporary rubber speed hump was initially installed as a one-month demonstration, after which the neighborhood supported a permanent installation. One month after implementation of the three recommended measures, the 85th percentile speed had decreased to 26.5 mph (a significant reduction from the pre-implementation speed of 35 mph).
New York City Neighborhood Slow Zone Program
New York City has embraced the Vision Zero concept that aims to eliminate all deaths from traffic crashes. The City made a commitment to improve street safety in every neighborhood and in every borough with expanded enforcement against dangerous moving violations like speeding and failing to yield to pedestrians, new street designs and configurations to improve safety, broad public outreach and communications, and a sweeping legislative agenda to increase penalties for dangerous drivers.
One element of the Vision Zero initiative is the Neighborhood Slow Zone Program. The program uses three primary tools to reduce motor vehicle speeds: gateway signage, 20 mph pavement markings, and speed humps.
Positive criteria used in the selection of candidate sites include crashes (crash injuries per mile and total injuries in the proposed zone), vulnerable populations (schools, daycares, senior centers), community support, subway stations, and a strong boundary with bus and truck routes. Negative criteria include fire stations, hospitals, and bus routes and truck routes internal to the zone.
With installation of 26 Neighborhood Slow Zones, the effects have included 10-25 percent reductions in vehicle speeds, a 10 percent overall reduction in crashes with injuries, and a 27 percent reduction in vehicle crash injuries.
A summary of the overall program and detailed individual project results can be accessed at the following hyperlink:
http://www.nyc.gov/html/dot/html/motorist/slowzones.shtml
Seattle Safe Routes to School Program
The overall objective of the Seattle Safe Routes to School program is to make it easier and safer for students to walk and bike. The program has five essential components:
- Engineering: To build new sidewalks and curb ramps, improve crosswalks, coordinate with neighborhood greenways, and promote safe driving;
- Education: To give pedestrian and bicycle safety skills and knowledge to kids and families
- Encouragement: To get more parents involved in their kids' schools and get kids more familiar with their neighbors and community
- Enforcement: To make sure everyone obeys the rules of the road and traffic circulation plans adopted by school communities
- Evaluation: To make sure the programs are achieving their goals
The Seattle Department of Transportation developed an Engineering Toolkit that presents 16 strategies that are used in Seattle. Five of the listed strategies are covered in depth in this ePrimer:
- Crossing Treatments
- Crossing islands (considered a median island in ePrimer)
- Curb bulbs (considered a corner extension or choker in ePrimer)
- Curb ramps
- Marked crosswalks
- Crossing beacons
- 20 mph zones
- Traffic signals
- Stop signs
- Along the Street Treatments
- Sidewalks
- Bikeways
- Radar speed signs
- Lane reduction (considered a road diet in ePrimer)
- Traffic Calming
- Speed humps and cushions (considered speed humps, speed cushions,
- and speed tables in ePrimer)
- Traffic circles (covered in ePrimer)
- Neighborhood greenways
- Other
- Bicycle parking
The Engineering Toolkit provides references, resources, and examples in Seattle for each strategy. The Toolkit also answers four questions:
- What is the purpose of [strategy]?
- How does Seattle DOT decide where to install [strategy]?
- How much does [strategy] cost?
- How long does it take to install [strategy]?
The complete toolkit can be accessed at the following hyperlink:
Portland (Maine) Traffic Calming Study – Massachusetts Avenue Neighborhood
The traffic calming study area is a residential neighborhood through which vehicular traffic was determined to be cutting through in order to avoid traffic congestion on nearby streets. The neighborhood is served by nine neighborhood streets, each about one-half mile in length. Current AADT on the nine streets ranged between 285 and 1,140.
A series of speed humps, traffic circles, and all-way Stops were installed throughout the neighborhood. The purpose of the case study was to assess the effectiveness of the traffic calming measures to reduce cut-through traffic volumes and vehicle speeds. The post-implementation evaluation was determined to be too soon to enable an accurate assessment of overall and site-specific crash rate changes.
Speed and vehicle count data were collected at nine locations along the neighborhood streets.
- 85th percentile vehicle speeds were found to decrease at all nine locations.
- Mean vehicle speeds were found to decrease at seven locations and to remain the same at one location. For the one location with an increase in mean speed, the hypothesis is that a change in counting equipment affected the results. The pre-implementation data at this site only were collected with tube counters that were visible to the motorist (and may have resulted in more caution and slower speed). The post-implementation data were collected with a radar recorder.
- Estimated AADT was found to decrease at six of the nine locations. The pre- and post-implementation data were collected during the months of April 2013 and June 2015, respectively. The count data were factored to represent AADT with the use of seasonal factors that reflect areawide facility type seasonal variations. The hypothesis for the inconsistent changes in neighborhood street traffic volumes is the use of seasonal factors that may not accurately reflect variations in this particular neighborhood. In addition, the proximity to athletic fields for several of the streets is likely to have skewed the seasonal variation factoring.
A summary report can be accessed at the following hyperlink: http://gorrillpalmer.com/services/transportation/
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ii Robertson, Taylor. (2000). "Speed Hump Impacts on Emergency Response Times Eugene Fire and Emergency Medical Services." Eugene Fire and Emergency Medical Services.
iii Robertson, Taylor. (2000). "Speed Hump Impacts on Emergency Response Times Eugene Fire and Emergency Medical Services." Eugene Fire and Emergency Medical Services.
iv Portland Bureau of Fire, Rescue and Emergency Service and Bureau of Traffic Management Portland Department of Transportation. (January 1996). "The Influence of Traffic Calming Devices on Fire Vehicle Travel Times." Portland, Oregon.
v Montgomery County Fire and Rescue Commission. (August 1997). "The Effects of Speed Humps and Traffic Circles on Responding Fire-Rescue Apparatus in Montgomery County, Maryland." Montgomery County, Maryland.
vi Gulden, J., and Ewing, R. (January 01, 2009). New Traffic Calming Device of Choice. ITE Journal, 79, 12, 26-31.
vii Gulden, J., and Ewing, R. (January 01, 2009). New Traffic Calming Device of Choice. ITE Journal, 79, 12, 26-31.
viii Gulden, J., and Ewing, R. (January 01, 2009). New Traffic Calming Device of Choice. ITE Journal, 79, 12, 26-31.
ix Chang, K. N., Nolan, M., and Nihan, N. L. (January 01, 2007). Developing Design Standards for Speed Cushions. Transportation Research Record, 2030, 22-28.
x Batson, S. (March 2004). "Offset Speed Tables for Reduced Emergency Response Delay." ITE Technical Conference, Irvine, California.
xi Batson, S. (March 2004). "Offset Speed Tables for Reduced Emergency Response Delay." ITE Technical Conference, Irvine, California.
xii Montgomery County Fire and Rescue Commission. (August 1997). "The Effects of Speed Humps and Traffic Circles on Responding Fire-Rescue Apparatus in Montgomery County, Maryland." Montgomery County, Maryland.
xiii Ewing, R. H., and Institute of Transportation Engineers. (1999). Traffic Calming: State of the Practice. Washington, DC: Institute of Transportation Engineers.
xiv Nuttall, S. (February 1999). "The Impact of Traffic Calming Devices on Emergency Fire Response." Bellevue Fire Department, Bellevue, Washington.
xv Nuttall, S. (February 1999). "The Impact of Traffic Calming Devices on Emergency Fire Response." Bellevue Fire Department, Bellevue, Washington.
xvi ITE Traffic Engineering Council. (2007). Guidelines for the Design and Application of Speed Humps. Institute of Transportation Engineers, Washington, D.C.
xvii Barthod, C. (2011). "Traffic Calming Speed Humps and Speed Cushions." 2011 Annual Conference of the Transportation Association of Canada, Edmonton, Alberta, Canada.
xviii Barthod, C. (2011). "Traffic Calming Speed Humps and Speed Cushions." 2011 Annual Conference of the Transportation Association of Canada, Edmonton, Alberta, Canada.
xix Atkins, C. and Wilson, E. (1998). "Balancing the Tradeoffs – How the City of Portland, Oregon Resolved the Conflict Between Traffic Calming and Emergency Response Services." Institute of Transportation Engineers, Washington, D.C.
xx Portland Bureau of Fire, Rescue and Emergency Service and Bureau of Traffic Management Portland Department of Transportation. (January 1996). "The Influence of Traffic Calming Devices on Fire Vehicle Travel Times." Portland, Oregon.
xxi Montgomery County Fire and Rescue Commission. (August 1997). "The Effects of Speed Humps and Traffic Circles on Responding Fire-Rescue Apparatus in Montgomery County, Maryland." Montgomery County, Maryland.
xxii Montgomery County Fire and Rescue Commission. (August 1997). "The Effects of Speed Humps and Traffic Circles on Responding Fire-Rescue Apparatus in Montgomery County, Maryland." Montgomery County, Maryland.
xxiii Montgomery County Fire and Rescue Commission. (August 1997). "The Effects of Speed Humps and Traffic Circles on Responding Fire-Rescue Apparatus in Montgomery County, Maryland." Montgomery County, Maryland.
xxiv Fox, W. and Noyes, P. (March 1998). "Neighborhood Traffic Management Process and Results." ITE International Meeting, Monterey, California.
xxv Robertson, Taylor. (2000). "Speed Hump Impacts on Emergency Response Times Eugene Fire and Emergency Medical Services." Eugene Fire and Emergency Medical Services.
xxvi Robertson, Taylor. (2000). "Speed Hump Impacts on Emergency Response Times Eugene Fire and Emergency Medical Services." Eugene Fire and Emergency Medical Services.
xxvii Fox, W. and Noyes, P. (March 1998). "Neighborhood Traffic Management Process and Results." ITE International Meeting, Monterey, California.
xxviii Robertson, Taylor. (2000). "Speed Hump Impacts on Emergency Response Times Eugene Fire and Emergency Medical Services." Eugene Fire and Emergency Medical Services.
xxix Bunte, Leslie. (May 2000). "Traffic Calming and Emergency Response: A Competition of Two Public Goods". University of Texas at Austin
xxx Nuttall, S. (February 1999). "The Impact of Traffic Calming Devices on Emergency Fire Response." Bellevue Fire Department, Bellevue, Washington.
xxxi DeRobertis, M and Wachtel, A. (September 1996). "Traffic Calming – Do's and Don'ts to Encourage Bicycling." Compendium of Technical Papers for the 66th ITE Annual Meeting, Minneapolis, Minnesota.
xxxii ITE Traffic Engineering Council. (2007). Guidelines for the Design and Application of Speed Humps. Institute of Transportation Engineers, Washington, D.C.
xxxiii Daniel, J., Chien, S., and Liu, R. (2005). Effectiveness of Certain Design Solutions on Reducing Vehicle Speeds. New Jersey Institute of Technology and New Jersey Department of Transportation, Trenton, New Jersey.
xxxiv Daniel, J., Chien, S., and Liu, R. (2005). Effectiveness of Certain Design Solutions on Reducing Vehicle Speeds. New Jersey Institute of Technology and New Jersey Department of Transportation, Trenton, New Jersey.
xxxv Johnson, R. S. (2005). Pedestrian Safety Impacts of Curb Extensions: A Case Study. Oregon Department of Transportation, Research Unit, Salem, Oregon.