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Speed Bumps

Bureau of Traffic Management TRAFFIC MANUAL
CHAPTER 11 - SPEED BUMPS

City of Portland, Oregon
December 20, 1994

 
TABLE OF CONTENTS
 
Index No  
11-01 INTRODUCTION AND GENERAL STANDARDS
11-01.1 Function of Speed Bumps
11-01.2 Scope of Speed Bump Standards
11-01.3 Legal Authority
11-01.4 Standardization of Application
11-01.5 Types of Speed Bumps
11-01.6 Generalized Standards and Guidelines
11-01.11 Construction and Maintenance
11-02 14 FOOT SPEED BUMPS
11-02.1 Application of 14 Foot Speed Bumps
11-02.2 Design of 14 Foot Speed Bumps
11-02.3 Placement of 14 Foot Speed Bumps
  14 Foot Speed Bump Specifications
11-03 22 FOOT SPEED BUMPS
11-03.1 Application of 22 Foot Speed Bumps
11-03.2 Design of 22 Foot Speed Bumps
11-03.3 Placement of 22 Foot Speed Bumps
  22 Foot Speed Bump Specifications
 
CHAPTER 11 SPEED BUMPS
Introduction and General Standards 11-01
 
11-01.1 Function of Speed Bumps
 
Speed bumps are traffic management devices used for lowering the speed of motor vehicles along specific street sections. Speed bumps should be used only when justified by field studies.
 
11-01.2 Scope Speed Bump Standards
 
This chapter prescribes standards and guidelines for the application of speed bumps in the public right-of-way on streets classified as either "local service" or "neighborhood collector" class streets as defined in the Transportation Element of the City of Portland's Comprehensive Plan. The use of speed bumps on streets of other classification is currently not allowed. Standards for 14 Foot Speed Bumps are found in Section 11-02. Standards for 22 Foot Speed Bumps are found in Section 11-03
 
11-01.3 Legal Authority
 
Speed bumps shall be placed only by the authority of the City Traffic Engineer in accordance with Title 16 of the City of Portland Municipal Code.
 
The installation of an unauthorized speed bump by a private organization or individual is unlawful according to Title 17.40 of the City of Portland Municipal Code.
 
11-01.4 Standardization of Application
 
Through the strict adherence to standards and guidelines outlined in this manual, any given speed bump installation will be equally recognizable and require the same action on the part of the motorists regardless where it is encountered. Unique, "non-standard" situations may warrant unique treatment where justifiable based on a comprehensive engineering evaluation and approval by the City Traffic Engineer.
 
Speed bumps should be installed only for the specific purpose prescribed for in this manual.
 
The application of speed bumps on City streets shall ordinarily be made in accordance with the criteria set forth in this manual. However, as with other traffic control devices, engineering judgment is essential to the proper use of speed bumps. Traffic engineering studies may indicate that speed bumps would be unnecessary or unsafe at certain locations. Data obtained from traffic engineering studies of physical and traffic related factors should be used in determining where speed bumps are appropriate.
 
11-01.5 Types of Speed Bumps
 
There are two types of speed bumps that have been adopted for use by the City of Portland:
 
A. 14 FOOT SPEED BUMP - For use primarily on lower volume local service streets as defined in the Transportation Element (TE) of the Comprehensive Plan. See Section 11-02 Local Speed Bump for more detail.
 
B. 22 FOOT SPEED BUMP - For use on both neighborhood collector streets and higher volume and speed local service streets as defined in the TE. Also may be used on local service streets that serve as primary fire response routes. See Section 11-03 Arterial Speed Bump for more detail.
 
11-01.6 Generalized Standards and Guidelines
 
The following are general standards and guidelines that apply to all speed bump applications. There may be situations which do not meet all criteria.
 
A. GRADE - Speed bumps may be installed on street sections with a grade equal to, or less than 5-percent. The installation of speed bumps on street sections with a grade greater than 5-percent must be based on an engineering evaluation to assure that the installation will not create inappropriate risks to traffic safety. Speed bumps may not be installed on street sections with grades greater than 8-percent(1).
 
B. PROXIMITY TO CURVE - Prior to placing speed bumps along horizontal roadway curvature, an engineering evaluation should be conducted to assure that the speed bump installation in conjunction with the design speed of the curve(s) will accommodate safe vehicle passage. In addition, speeds bumps and/or speed bump warning signs should be placed in such a manner as to be clearly visible by approaching motorists according to MUTCD guidelines for visibility and reaction times.
 
C. STREET CONDITION - The Maintenance Bureau should inspect all streets prior to any proposed bump construction. The Maintenance Bureau will determine if the existing street pavement conditions are adequate to support the impact loads caused by the bumps and if any pavement maintenance is required. If it is determined that improvements or maintenance is required, that work should be completed before bumps are constructed.
 
D. CURBS - Speed bumps may be installed on streets without curbs. However, in order to avoid potential circumnavigation around bumps at location without curbs, precautions, such as the installation of road side delineators, may need to be taken.
 
E. DRIVEWAYS - Construction of speed bumps at a driveway location should be avoided where possible to reduce potential vehicle conflict.
 
F. PARKING - No special parking removal is required on or near speed bumps.
 
G. DIVERSION POTENTIAL - Adjacent streets, identified by the engineer, as having potential for being impacted by vehicle diversion from the street being treated with speed bumps should be monitored.
 
H. BUS STOPS/ZONES - Where possible, speed bumps should not be installed in street sections where transit vehicles must transition between the travel lane and curb stop. To the extent possible, speed bumps should be located in such a way as to ensure that transit vehicles can traverse the bump perpendicularly.
 
I. SPACING - Speeds bumps installed in series should be spaced according to an engineering evaluation of the physical street section as well as traffic operations data. Typically, speed bumps are spaced at between 300 and 600 feet apart.
 
J. UTILITIES - Speed bumps should be located in such a way as to avoid conflict with underground utility access to boxes, vaults and sewers.
 
K. TRAVEL LANES - Speed bumps shall not be installed on streets with more than one through travel lane per direction. Speed bumps shall not be installed in exclusive left-turn or right-turn lanes. Special care should be exercised when considering speed bumps on streets with continuous left-turn lanes. In all cases, speed bumps shall be constructed across the entire width of street surface.
 
11-01.7 Construction and Maintenance of Speed Bumps
 
A. CONSTRUCTION - Speed bumps may be constructed by the Bureau of Maintenance or by a private contractor per the appropriate Standard Plan as approved by the City Traffic Engineer.
 
B. CONSTRUCTION TOLERANCES - Speed bumps must be constructed per the appropriate Standard Plan within a tolerance of +/- 0.5-inches in height.
 
C. ROAD/UTILITY WORK - Any speed bump, including any associated pavement markings or signage, that is damaged by road or utility work shall be repaired to the original condition by the utility agency responsible for the damage.
 
D. MAINTENANCE - Speed bumps shall be maintained by the Bureau of Maintenance.
 
E. MONITORING - The Bureau of Maintenance will monitor speed bumps as well as associated signing and markings for necessary maintenance. In addition, while under development and research, speed bumps will be monitored by Bureau of Traffic Management staff to observe and evaluate wear and maintenance requirements.
 
14 Foot Speed Bump 11-02
 
11-02.1 Application of 14 Foot Speed Bump
 
A. STREET CLASSIFICATION-14 foot speed bumps are limited for use on local service streets only, as defined in the in the Transportation Element of the Comprehensive Plan.
 
B. PREVAILING SPEED- 14 foot speed bumps are most appropriate for street sections with an 85th percentile speed between 25 mph and 35 mph. 14 foot bumps should not be used on street sections with an 85th percentile speed of less than 25 mph(2). For street sections with 85th percentile speeds in excess of 35 mph, 14 foot speed bumps may be inappropriate(3). The provision of 14 foot bumps on street sections with 85th percentile speeds greater than 35 mph should be based on careful evaluation of the street section, land-use, traffic-type, traffic volumes, etc..
 
14 foot speed bumps should not be used on street sections with an 85th percentile speed of 40 mph or greater.
 
11-02.2 Design of 14 Foot Speed Bumps
 
A. SHAPE-The 14-foot long vertical cross-section of the 14 foot speed bump, measured in the direction of traffic flow, shall be a parabolic curve with a maximum height of 3-inches at the mid-point, and be 14-feet in length as detailed in Plan No. 3-181 of the City's Standard Construction Specifications.
 
B. SIGNING AND PAVEMENT MARKINGS-14 foot speed bumps shall be accompanied by appropriate signing and pavement markings as detailed in Plan No. 3-181 of the City's Standard Construction Specifications.
 
 
11-02.3 Placement of 14 Foot Speed Bumps
 
Where possible, 14 foot speed bumps should be located at least 60 feet from the closest perpendicular extension of an intersecting street curb or pavement edge line.(4)
 
22 Foot Speed Bump 11-03
 
11-03.1 Application of 22 Foot Speed Bump
 
A. STREET CLASSIFICATION-22 foot speed bumps are limited for use on local service streets and neighborhood collectors streets only, as described in the Transportation Element of the Comprehensive Plan.
 
B. PREVAILING SPEEDS- 22 foot speed bumps are most appropriate for street sections with 85th percentile speeds between 35 and 45mph(5). 22 foot bumps should not be used on street sections with 85th percentile speeds less than 30 mph(6), except when the street sections are on primary fire response routes. The provision of 22 foot speed bumps on street sections with 85th percentile speeds greater than 45 mph should be based on careful evaluation of the street section, land-use, traffic-type, traffic volumes, etc.(7).
 
22 foot speed bumps should not be used on street sections with an 85th %-ile speed of 50 mph or greater.
 
11-03.2 Design of 22 Foot Speed Bump
 
A. SHAPE-The 22-foot long vertical cross-section of the 22 foot speed bump, measured in the direction of traffic flow, shall consist of a 10 foot horizontal platform, 3-inches in height which transitions at both ends to existing pavement level by way of 6-foot parabolic curves, as detailed in Standard Plan No. 3-180 of the City's Standard Construction Specifications.
 
B. SIGNING AND PAVEMENT MARKINGS-22 foot speed bumps shall be accompanied by appropriate signing and pavement markings as detailed in Standard Plan No. 3-180 of the City's Standard Construction Specifications.
 
11-03.3 Placement of 22 Foot Speed Bump
 
Where possible, 22 foot bumps should be located at least 100 feet from the closest intersecting curb or pavement edge line.(8)
 
Footnotes

 
1. Based on ITE Draft Speed bump Guidelines.
 
2. Residential speed limit under statutory law.
 
3. Eighty-fifth percentile speed is an excellent indicator of street character. The application of a speed reduction device, which lowers the 85th percentile speed at device locations, more than 15 miles per hour will tend to create a pronounced "sine wave" type velocity profile. For many higher volume streets, such a velocity profile may be inappropriate both with regards to traffic safety and/or the noise of acceleration and deceleration. Since research has indicated that 14 foot speeds bumps reduce 85th percentile speeds to approximate 20 mph, the use of 14 foot speed bumps on streets with 85th percentile speed in excess of 35 mph may be inappropriate.
 
4. The placement of 14 foot speed bumps at a minimum of 60 feet from the closest intersecting curb or pavement line will assure that all bump related pavement markings remain outside the intersection and ensure that vehicles turning from the side street will engage the bump in a perpendicular fashion.
 
5. 22 foot speed bumps are yet to be tested on street segments with 85th percentile speeds between 40 and 45 mph.
 
6. Research has indicated that the 22 foot speed bump is effective in reducing 85th percentile speeds to approximately 30 mph. The use of 22 foot speed bumps on street section with 85th percentile speeds less than 30 mph would be ineffective.
 
7. Eighty-fifth percentile speed is an excellent indicator of street character. The application of a speed reduction device, which lowers the 85th percentile speed at device locations, more than 15 miles per hour will tend to create a pronounced "sine wave" type velocity profile. Such a velocity profile may be inappropriate both with regards to traffic safety and/or the noise of acceleration and deceleration. Since research has indicated that 22 foot speeds bumps reduce 85th percentile speeds to approximate 30 mph, the use of 22 foot speed bumps on streets with 85th percentile speed in excess of 45 mph may be inappropriate.
 
8. The placement of 22 foot speed bumps at a minimum of 100 feet from the closest intersecting curb or pavement line will assure that all bump related pavement markings remain outside the intersection and ensure that vehicles turning from the side street will engage the bump in a perpendicular fashion.