HomeMy WebLinkAboutTrans 2012-08-06 Item 2A - Ordinance - Tukwila International Boulevard Speed StudyCity of Tukwila
Jim Haggerton, Mayor
INFORMATIONAL MEMORANDUM
TO: Mayor Haggerton
Transportation Committee
FROM: Bob Giberson, Public Works Director
DATE: August 3, 2012
SUBJECT: Tukwila International Boulevard Speed Study
Ordinance Establishing New Speed Limits
ISSUE
Should the speed limit be reduced on Tukwila International Boulevard (TIB)?
BACKGROUND
After completion of the Tukwila International Boulevard Improvements (Phases I, II, and III), Public
Works was asked to analyze the existing speed limit. Speed limits are set after conducting a full
engineering evaluation of speeds, collisions, and related information.
An engineering speed study was just completed by a traffic engineering consultant for the southern
portion of Tukwila International Boulevard. The limits of the study are S 116th Way on the north and
S 152nd St on the south end of Tukwila International Blvd. These are the same limits as TIB Phases
I, II, and III combined. The consultant studied speeds, volumes, and collision rates. The 85th
percentile speed is typically used to set speed limits based on the theory that most drivers will travel
at a speed that is reasonable and prudent for any given roadway segment. The 85th percentile speed
is the speed at or below which 85 percent of the motorists drive on a given road unaffected by
slower traffic or poor weather. This indicates the speed that most motorists on the road consider safe
and reasonable under ideal conditions.
ANALYSIS
The 85th percentile speeds are shown in Table 1 (page 4) of the speed study. The 85th percentile
speeds for the area north of S 139th are in excess of the 45 mph posted speed limit, while the area in
between S 139th St and S 152nd St are below the posted speed limit.
Collision rates for the limits of the study area are summarized in Table 2 (page 7) of the speed study.
Data from the previous full five years was analyzed and the predominate collision type was found to
be rear end and the typical location was at mid -block crosswalks, driveways, and approaches to
traffic signals. To help mitigate the high rear end collision rate, the mid -block crosswalks near the
14300 and 15100 blocks are proposed to be retrofitted in 2013 as part of the new ADA crosswalk
project in the draft 2013 Capital Improvement Program.
RECOMMENDATION
Council is being asked to approve the Ordinance which will lower the speed limit from 40 mph to 35
mph on Tukwila International Boulevard between South 139th Street and South 152nd Street and
consider this item at the August 13, 2012 Committee of the Whole meeting and subsequent August
20, 2012 Regular Meeting.
Attachments: Speed Study
Draft Ordinance
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Memorandum
To: Bob Giberson, Public Works Director, City of Tukwila
CC: Robin Tischmak, Public Works, City of Tukwila
From: Jan Ciganik, P.E., P.T.O.E.
Date: June 13, 2012
Re: Tukwila International Boulevard Speed Study
Project No: 12028
This memorandum summarizes the results of a speed study performed on Tukwila International
Boulevard between 5 152ND St to the south and SR -599 to the north. Data was gathered at five
locations along the corridor, with speed and traffic volumes being recorded. This memorandum
will discuss the following:
• Roadway Description
• Speed and Volume Data Collection and Results
• Speed Data Analysis
• Collision Data
• Results and Recommendations
Roadway Description
Tukwila International Boulevard (TIB) is a Major Arterial that consists of a five lane cross section
with a two - way -left- turn -lane or center medians between S 152nd St and the 12400 block and a
four lane cross section between the 12400 block and the SR -599 interchange. TIB serves as a
major north -south route providing access to SR -518 to the south and SR -599 to the north; the
roadway length between these two interchanges is approximately 2.5 miles.
The traffic along this roadway is comprised of commuter traffic from the surrounding
neighborhoods. Land use varies along the corridor between commercial businesses located
between S 152nd St and S 139th Street and office buildings located near the 12400 block.
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Speed and Volume Data Collection and Results
Speed data and traffic volumes were collected at five locations along the corridor during late
March, 2012. Data was collected for each lane utilizing separate counters. The locations studied
are shown graphically in Exhibits 1, 2 and 3 in Appendix A and listed below.
• Site 1 - Tukwila International Boulevard midway between S 150th St and S 148th St
• Site 2 - Tukwila International Boulevard midway between S 146th St and S 144th St
• Site 3 - Tukwila International Boulevard north of S 139th St
• Site 4 - Tukwila International Boulevard north of S 130th St
• Site 5 - Tukwila International Boulevard at approximately the 12000 block
To evaluate vehicle speeds, multiple measures should be considered. These measures are
included in Table 1 (next page) and explained below:
Median Speed — Median speed is the speed at which half of the vehicles travel above and half
travel below.
85t" Percentile Speed — The 85th percentile speed is the speed in which 85 percent of vehicles
travel at or below. The 85th percentile should typically be within 5 -10 mph of the posted speed
limit. According to the Institute of Transportation Engineers, studies have shown that crash rates
are lowest when drivers are traveling near the 85th percentile speed.
10 mph Pace — The 10mph pace is a consecutive 10mph range of speeds containing the highest
number of vehicles.
Percent Flagrant Speeding — The percent flagrant speeding represents the percentage of vehicle
exceeding the speed limit by at least 10mph.
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Table 1. Speed Data and Traffic Volumes
Speed Median 85th 10 MPH
Site Limit ADT Direction Lane Speed Percentile Pace
(MPH) (MPH) Speed (MPH) (MPH)
Percent Flagrant
Speeding
1 40 17,364
Curb 32.4 37.8 28.5 - 38.5
NB
Median 34.8 39.8 30.0 - 40.0
0.0%
0.1%
SB
Median 33.2 38.2 28.3 - 38.3 0.1%
*Curb 43.2 47.7 38.7 - 48.7 5.5%
2 40 18,054
NB
Curb 31.9 37.2 27.2 - 37.2
Median 34.9 39.9 30.2 - 40.2
0.1%
0.3%
SB
Median 30.4 35.9 25.7 - 35.7
Curb 27.9 33.9 23.3 - 33.3
0.1%
0.0%
3 45 12,841
NB
Curb 41.4 46.5 34.9 - 44.9
Median 43.0 48.6 37.2 - 47.2
0.7%
1.6%
SB
Median 43.1 47.7 38.2 - 48.2
Curb 41.4 46.5 37.2 - 47.2
0.7%
0.9%
4 45 12,996
NB
SB
Curb 43.0 48.6 37.2 - 47.2
Median 44.7 50.8 41.4 - 51.4
1.0%
3.8%
Median 44.7 50.8 41.4 - 51.4
Curb 43.0 48.6 37.2 - 47.2
3.6%
2.3%
5 45 11,481
NB
Curb 45.8 51.2 41.4 - 51.4
Median 47.4 52.8 42.3 - 52.3
5.0%
7.5%
SB
Median 44.8 50.1 40.2 - 50.2
Curb 43.6 49.0 37.7 - 47.7
4.0%
1.6%
*NOTE: SB Curb Lane values at Location 1 were omitted due to apparent error in data collection.
Median Speed - The median speed is below the speed limit in all locations except for Location 5 in
the northbound direction.
85th Percentile Speed - Locations 1 and 2 (with the exception of the southbound curb lane at
location 1) have 85th percentile speeds below the posted speed limit of 40 mph. Locations 3, 4 and
5 have 85th percentile speeds in excess of the posted speed limit of 45 mph.
10 mph Pace - Locations 1 & 2 have a 10 mph pace that is below the speed limit, while locations 3,
4 & 5 have a 10 mph pace that ranges above and below the speed limit
Percent Flagrant Speeding - Locations 1 & 2 have the lowest percentage of flagrant speeding,
while locations 4 & 5 have the highest.
The complete volume and speed data is provided in Appendix B.
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KPG
Speed Data Analysis
Figure 1 and Figure 2 provide visual representation of the 85th Percentile and 50th Percentile
(Median) Speeds with respect to the speed limit.
60
s 50
E
Is 40
a,
a
N
a, 30
c
a,
y 20
a
s
L
o`^0 10
0
Posted Speed Limit
- NB Curb
- NB Median
- SB Median
- SB Curb
1 2 3
Location
4
5
Note:
SB Curb Lane
speeds at
Location 1 were
omitted due to
apparent data
collection errors
Figure 1— 85th Percentile Speed with respect to Speed Limit
As can be seen from Figure 1, the 85th Percentile Speed is at or below the speed limit for Locations
1 and 2, then it rises above the speed limit for Locations 3 through 5.
60
E 50
CU
CU
0 40
c
• 30
v
a, 20
a,
v 10
a
s
0
Posted Speed Limit
- NB Curb
- NB Median
- SB Median
- SB Curb
1 2 3 4 5
Location
Figure 2 — 50th Percentile (Median) Speed with respect to Speed Limit
Note:
SB Curb Lane
speeds at
Location 1 were
omitted due to
apparent data
collection errors
As can be seen from Figure 1, the Median Speed is below the speed limit for Locations 1 through 4,
then it rises at or above the speed limit at Location 5.
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Collision Data
Collision data for Tukwila International Boulevard between S 116th St and S 152nd St was provided
by the City of Tukwila for the 5 years prior to this memo; January 1, 2007 — December 31, 2011.
All of the collision data has been summarized graphically, by location and type, in Exhibits 1, 2 and
3 as attachments to this memo.
During the 5 year time period, there were 353 collisions, 168 of which occurred at an intersection
and 185 which occurred between intersections. There were a total of 699 vehicles involved
resulting in 104 injuries and one fatality during the time period.
Collisions by Type
As can be seen from Figure 3, the most common type of collision was Rear End. These typically
occurred near mid -block pedestrian crossings, driveways or at approaches to signalized
intersections. Right angle collisions were the second most common type, with 80% of them
occurring at intersections.
Head On, 4
Approach
Pedestrian/ Turn, 30
Cyclist
Involved, 15
Fixed
Object /Park
ed Vehicle,
34
Backing, 6
RightAngle,
84
Figure 3 — Collisions along TIB, by type
Rear End,
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Collisions Rates
Collision rates were calculated for each segment and are provided in Table 2. The rates for spot
locations (intersections) are reported in collisions per million vehicles and rate for roadway
sections are reported in collisions per 100 million vehicle miles. Rates are calculated per the
following equations:
Collision Rates for Intersections
Collision Rates for Roadway Sections
Number of Collisions x 106
ADT x 365 x Number of Years
Number of Collisions x 108
ADT x 365 x Number of Years x Length
Table 2. Collision Rates by Intersection and Segment
Location
Total
C Ilisions
ADT
Di trance
Intersection
Collision Rate
(c /mev)
Roadway Segment
Collision Rate
(c /100mvm)
TIB at S 152 ST
5
17364
0.16
Between S 152 ST and S 150 ST
40
0.12
1052
TIB at S 150 ST
22
0.69
Between S 150 ST and S 148 ST
12
0.12
316
TIB at S 148 ST
21
0.66
Between S 148 ST and S 146 ST
15
0.12
394
TIB at S 146 ST
25
18054
0.76
Between S 146 ST and S 144 ST
25
0.11
717
TIB at S 144 ST
21
0.64
Between S 144 ST and S 142 ST
19
0.12
500
TIB at S 142 ST
4
0.12
Between S 142 ST and S 141 ST
6
12841
0.09
210
TIB at 5141 ST
3
0.13
Between S 141 ST and S 140 ST
4
0.04
316
TIB at S 140 ST
14
0.60
Between S 140 ST and S 139 ST
5
0.06
263
TIB at 5139 ST
4
0.17
Between S 139 ST and 37 AVE S
6
0.39
49
TIB at 37th Ave S
11
0.47
Between 37 AVE S and S 133 ST
2
0.10
63
TIB at S 132 ST
10
0.43
Between S 132nd ST and S 130 ST
9
12996
0.12
237
TIB at S 130 ST
4
0.17
Between S 130 ST and S 128 ST
24
0.12
631
Between S 128 ST and S 116 ST
15
11481
0.70
68
TIBatS116ST
24
1.15
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Results and Recommendations
The speed, volume and collision data has been analyzed using the data provided, Engineering
judgment and site visits. Recommendations will be provided based on industry best practices and
field observations.
Speed
Speeding was found to be a minor issue at two locations along the corridor; locations four and
five. The difference in speed throughout the corridor is likely due to the difference in land use and
density of intersections and driveways. Surrounding locations four and five there are two
signalized intersection and very few driveways, compared to four signalized intersections, eight
unsignalized intersections, two mid -block pedestrian crossings and numerous driveways along the
rest of the corridor.
Possible corrective measures could include providing radar driver feedback signs that provide real -
time feedback to drivers exceeding the speed limit. This should also be supplemented with
increased enforcement of the speed limit.
Collisions
Two locations were identified as having higher than typical collision rates for the corridor:
• TIB between S 152nd St and S 150th St
• TIB at S 116th Way
Field investigation was conducted to determine possible causes for high collision rates.
Between S 152nd St and S 150th St rear -end collisions comprised the majority (72.5 %) of total
collisions for the segment and many occurred near the mid -block pedestrian crossing. The existing
mid -block crossing provides overhead signage and in- pavement flashing amber lights. The in-
pavement lights are not effective at alerting the entire platoon of vehicles as they are blocked by
the vehicle stopped nearest to the crosswalk. Modifications to the warning system could reduce
the number of rear -end collisions. Overhead and post- mounted rapid - flashing beacons would
provide additional warning all drivers in the platoon, reducing the likelihood of sudden stopping
and rear -end collisions. Existing overhead mast arms could be utilized to reduce the cost of the
installation.
At the Intersection of TIB and S 116th Way, approach turn collisions were the most common
collision type. Upon further investigation of the data, the number of total collisions (including
approach turn collisions) significantly decreased after 2007. This is likely due to the conversion of
the protective /permissive left turns to protected -only in the northbound and southbound
directions. As a result of a site visit, it is recommended that the city install additional street -name
and guide signage at the intersection. Additional signage could result in less driver confusion,
leading to fewer collisions.
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AFT
AN ORDINANCE OF THE CITY COUNCIL OF THE CITY OF
TUKWILA, WASHINGTON, AMENDING ORDINANCE NOS.
1875 §1 AND 1866 §1, AS CODIFIED AT TUKWILA
MUNICIPAL CODE SECTION 9.16.070, TO ACCURATELY
DEFINE THE PORTION OF TUKWILA INTERNATIONAL
BOULEVARD BETWEEN SO. 139TH STREET AND SO. 152ND
STREET WHERE THE SPEED LIMIT IS TO BE REDUCED
FROM 40 MPH TO 35 MPH; PROVIDING FOR
SEVERABILITY; AND ESTABLISHING AN EFFECTIVE DATE.
WHEREAS, a portion of State Route 99, currently known as Tukwila International
Boulevard, was turned over to the City of Tukwila in 2003 by the state legislature; and
WHEREAS, RCW 46.61.415 authorizes the City to establish speed limits
determined by engineering and traffic studies; and
WHEREAS, an engineering evaluation of Tukwila International Boulevard between
So. 139th Street and So. 152nd Street was conducted; and
WHEREAS, based upon the engineering evaluation, the City has determined that
35 miles per hour (mph) is a reasonable and safe maximum limit on Tukwila
International Boulevard between So. 139th Street and So. 152nd Street;
NOW, THEREFORE, THE CITY COUNCIL OF THE CITY OF TUKWILA,
WASHINGTON, HEREBY ORDAINS AS FOLLOWS:
Section 1. Tukwila Municipal Code (TMC) Section 9.16.070, "Forty mph on
portion of Tukwila International Boulevard ", Amended. Ordinance Nos. 1875 §1
and 1866 §1, as codified at TMC Section 9.16.070, are hereby amended to read as
follows:
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9.16.070 Thirty- fiveFecty mph on portion of Tukwila International Boulevard
A 3548 mile per hour speed limit zone is established for both directions of traffic on
Tukwila International Boulevard (State Route 99) between So. 139th Street and So.
152nd Street
' == e -se
Section 2. Signs to Be Posted. The Public Works Department is hereby directed
to post appropriate speed limit signs reflecting the speed limit established in Section 1
of this ordinance.
Section 3. Corrections by City Clerk or Code Reviser. Upon approval of the
City Attorney, the City Clerk and the code reviser are authorized to make necessary
corrections to this ordinance, including the correction of clerical errors; references to
other local, state or federal laws, codes, rules, or regulations; or ordinance numbering
and section /subsection numbering.
Section 4. Severability. If any section, subsection, paragraph, sentence, clause or
phrase of this ordinance or its application to any person or situation should be held to be
invalid or unconstitutional for any reason by a court of competent jurisdiction, such
invalidity or unconstitutionality shall not affect the validity or constitutionality of the
remaining portions of this ordinance or its application to any other person or situation.
Section 5. Effective Date. This ordinance or a summary thereof shall be published
in the official newspaper of the City, and shall take effect and be in full force five days
after passage and publication as provided by law.
PASSED BY THE CITY COUNCIL OF THE CITY OF TUKWILA, WASHINGTON, at
a Regular Meeting thereof this day of , 2012.
ATTEST /AUTHENTICATED:
Christy O'Flaherty, MMC, City Clerk
APPROVED AS TO FORM BY:
Shelley M. Kerslake, City Attorney
Jim Haggerton, Mayor
Filed with the City Clerk:
Passed by the City Council:
Published:
Effective Date:
Ordinance Number:
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