REPORT TO COUNCIL
SUBJECT
Title
Informational Report on Traffic Calming Study Criteria Related to 85th Percentile Speed and Traffic Volumes
Report
COUNCIL PILLAR
Deliver and Enhance High Quality Efficient Services and Infrastructure
BACKGROUND
On June 17, 2022, the City Clerk’s Office received a written petition from a resident requesting traffic calming measures on Cabrillo Avenue between Lawrence Expressway and Nobili Avenue. At the October 4, 2022 City Council meeting, staff provided an update on the written petition and during Council discussion on the item, staff was directed to return to Council with additional information on the specific criteria required for Level 2 and Level 3 Traffic Calming Measures per the City’s Neighborhood Traffic Calming Program. Specifically, Council wanted additional information about the 1) 85th percentile speed and 2) traffic volumes.
This report will provide background information on the City’s Neighborhood Traffic Calming Program (Overview, Level 2 and Level 3 Criteria), information about the 85th percentile speed and traffic volume criteria, and a broad comparison of these criteria compared to other neighboring local jurisdictions.
Neighborhood Traffic Calming Program Overview: Staff analyzes traffic calming requests and recommendations in accordance with the City Council approved Neighborhood Traffic Calming Program (NTCP). The NTCP was established to address and resolve local neighborhood traffic concerns in a systematic manner. The NTCP guidelines (Attachment 1) are utilized by staff when analyzing traffic calming requests submitted by residents. Traffic calming requests and concerns can vary significantly and the NTCP offers three levels of traffic calming measures (i.e. improvements), which are dependent on the results of studies, data collection and analysis.
• Level 1: Education, public involvement, enforcement efforts, signing, striping, parking controls, and use of the City’s speed radar trailer.
• Level 2: Alterations of the neighborhood street which can include chokers, chicanes, gateways, and rumble strips to deter or prohibit a specific action.
• Level 3: Measures similar to Level 2 that may alter neighborhood streets, but these measures may also affect overall neighborhood access and require coordination for emergency response. Examples of Level 3 measures include speed humps, traffic circles, median barriers, forced turn channelization, and diagonal diverters.
NTCP Level 2/Level 3 Criteria: Within the NTCP are specific criteria for installation of Level 2 and 3 measures or devices. The full list is provided as Attachment 2 and below is a summary of key criteria:
• The street shall be a two-lane local residential street where the primary function is to provide access to abutting residences. At least 75 percent of street section must be developed residentially, where schools and parks qualify as residential units.
• The speed limit shall be 25 miles per hour or less.
• Traffic volumes shall be greater than 1,000 and less than 3,500 vehicles per day.
• 85th percentile speed exceeds 33 miles per hour on 25 mile per hour streets.
• Installation on a primary emergency response route and/or transit route will NOT be permitted.
• Installation will NOT be permitted where substantial diversions of traffic to other local streets may occur, i.e. move the displaced traffic onto adjacent residential streets.
• At least 70 percent of the impacted residents and 100 percent of residents within 100 feet of the proposed device location shall support the installation.
DISCUSSION
Council requested more information about two specific criteria (85th percentile speed and traffic volume) related to allowing Level 2 and/or Level 3 traffic calming measures per the NTCP.
85th Percentile Speed: One of the criteria for installation of Level 2 and Level 3 traffic calming measures is that “The 85th percentile speed shall exceed 33 miles per hour on 25 miles per hour streets.”
The 85th percentile speed is a metric that is a traffic engineering industry standard used primarily to set speed limits on public roadways. It is calculated by using speed data and determining the speed that 85 percent of drivers are traveling at or below. As an example, if speed data is collected for 100 vehicles on a given roadway and 85 percent of drivers (85 drivers) are traveling at 30 miles per hour or less, the 85th percentile speed is 30 miles per hour. Specifically, for the NTCP, the 85th percentile speed should be above 33 miles per hour to meet the criteria for a Level 2 or 3 traffic calming measure.
Traffic Volumes: An additional criterion in the NTCP for the installation of Level 2 and Level 3 traffic calming measures is that “Traffic volumes shall be greater than 1,000 and less than 3,500 vehicles per day.”
In other words, when traffic volume data is collected for a given roadway, only roadways that have traffic volumes between 1,000 to 3,500 vehicles per day are eligible for Level 2 and Level 3 traffic calming measures. The intent behind setting these values is to limit the amount of Level 2 and Level 3 traffic calming measures on residential roadways to those with moderate traffic levels (between 1,000 - 3,500 vehicles per day). It is important to note that Level 2 and Level 3 traffic calming measures require funding for construction and maintenance and can increase vehicle congestion and delays if allowed on roadways with significant traffic volumes (i.e. traffic volumes greater than 3,500 vehicles per day).
Comparison to Other Local Jurisdictions: Attachment 3 provides information related to the traffic calming programs in Sunnyvale, Mountain View, San Jose, Palo Alto, and San Mateo to provide a comparison with the City’s NTCP 85th percentile speed and traffic volume criteria. While all traffic calming programs have criteria that vary slightly, Santa Clara’s criteria related to speed and traffic volume is comparable to other local jurisdictions.
Included with the Adopted Biennial Capital Improvement Program Budget there is proposed funding in Fiscal Year 2025-2026 in the Streets and Highways Fund, Neighborhood Traffic Calming project which may be used to begin a review and update to the NTCP which includes an evaluation of the current NTCP, research into other jurisdictions traffic calming programs, and best practices, etc.
ENVIRONMENTAL REVIEW
The action being considered does not constitute a “project" within the meaning of the California Environmental Quality Act ("CEQA") pursuant to CEQA Guidelines section 15378(b)(5) in that it is an administrative activity that will not result in direct or indirect physical changes to the environment.
FISCAL IMPACT
There is no fiscal impact to the City other than administrative staff time and expense.
COORDINATION
This report has been coordinated with the City Attorney’s Office.
PUBLIC CONTACT
Public contact was made by posting the Council agenda on the City’s official-notice bulletin board outside City Hall Council Chambers. A complete agenda packet is available on the City’s website and in the City Clerk’s Office at least 72 hours prior to a Regular Meeting and 24 hours prior to a Special Meeting. A hard copy of any agenda report may be requested by contacting the City Clerk’s Office at (408) 615-2220, email clerk@santaclaraca.gov <mailto:clerk@santaclaraca.gov> or at the public information desk at any City of Santa Clara public library.
RECOMMENDATION
Recommendation
Note and File the Informational Report on Traffic Calming Study Criteria Related to 85th Percentile Speed and Traffic Volumes
Staff
Reviewed by: Craig Mobeck, Director of Public Works
Approved by: Office of the City Manager
ATTACHMENTS
1. Neighborhood Traffic Calming Program Guidelines
2. Criteria for Installation of Level 2 and 3 Devices
3. Traffic Calming Program Comparison