HomeMy WebLinkAboutTIC 2017-10-24 Item 2F - Discussion - Neighborhood Traffic Calming Program: Speed Cushion Implementation CriteriaCity of Tukwila
Allan Ekberg, Mayor
INFORMATIONAL MEMORANDUM
TO: Transportation and Infrastructure Committee
FROM: Robin Tischmak, Acting Public Works Director
CC: Mayor Ekberg
DATE: October 20, 2017
SUBJECT: Neighborhood Traffic Calming Program
Project No. 91610410
Speed Cushion Implementation Criteria
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ISSUE
Develop implementation criteria for traffic calming features that include speed cushions and/or
radar speed display signs on residential streets if funding is programmed in future budget cycles.
BACKGROUND
The City's Capital Improvement Program (CIP) has historically included a Neighborhood Traffic
Calming Program that is unfunded due to staffing needs. On June 9, 2017, a speed cushion pilot
project was implemented on South 160th St to determine the effectiveness of innovative speed
cushions in conjunction with radar speed display signs. This pilot project will remain in place for a
minimum of one year at S 160th St. Formal criteria are desired for the possible implementation of
similar improvements on other residential streets throughout the City in case funding is budgeted to
expand this effort into an ongoing program.
DISCUSSION
Traffic conditions on residential streets greatly affect neighborhood livability. Unnecessary through -
traffic and speeding in neighborhoods create safety hazards on residential streets. Traffic calming
measures can be implemented to reduce the negative effects of motor vehicle use, alter driver
behavior, and improve conditions for pedestrians and bicyclists.
In order to ensure that traffic calming concerns are addressed in an equitable manner, a
preliminary evaluation must be performed to assess the situation by reviewing important basic
criteria to determine if the street qualifies for traffic calming measures. The primary purpose of a
preliminary evaluation is to determine whether the speeding or accident history is significant
enough to warrant further action. It should be noted that traffic calming improvements will not be
recommended in locations where engineering judgment has determined that actions are not
warranted. The three criteria listed below are widely accepted engineering measures that provide a
consistent, data driven evaluation of conditions on a given street. Example qualifications play
include:
• Speeding: the speeding criteria is met if 15% of the motorists travel at 10 mph or more
above the posted speed limit.
• Volume: the traffic volume criteria is met if the volume for the Local Streets are less than
3,000 vehicles per day and Residential Collectors are less than 7,000 vehicles per day.
• Traffic Accidents: the number of accidents for Local Streets and Residential Collectors is
three or more in one year.
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Speed Cushion Implementation Criteria
October 20, 2017
Page 2
Other factors for consideration of traffic calming measures include:
• proximity to schools, parks, and other pedestrian generators/destinations
• lack of sidewalks
• accessibility and special needs issues
• bicycle accessibility
• roadway characteristics
• other situational considerations
If traffic calming improvements are warranted, a progressive approach may be recommended. Just
using speed limit display radar signs may provide an acceptable level of traffic control. The
installation of speed cushions, associated signage, and pavement markings may be determined to
be an appropriate action as a more permanent traffic control measure. Neighborhood feedback
should be gathered when considering the installation of speed cushions or any other significant
traffic calming features such as roadway bulb outs.
FINANCIAL IMPACT
A cost analysis using the S 160th St Speed Cushion Pilot Project was used to calculate an
average cost per speed cushion to be used for future estimating purposes. Material purchases
and installation labor cost approximately $11,000 per speed cushion. This also includes the
cost of a speed study after the installation.
An annual program to install speed cushions on two streets (average five speed cushions per
street) would require approximately $125,000 in funding. This would include: $5,000 for
design/data gathering; $110,000 for installation; and $10,000 in contingency. The estimated
cost to remove speed cushions and restore the street would be approximately $9,000.
One set of two speed display radar signs cost approximately $13,000. We will be purchasing
two more sets of radar signs this year. With the current inventory at three sets (one permanent
installation), the total will be five sets of radar speed signs in the City. With our current level of
staffing, we will be unable to maintain any additional radar signs above the five sets.
RECOMMENDATION
For discussion only.
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