22-102032-UP Traffic Impact Analysis-5-4-22 TENW
Transportation Engineering NorthWest
Transportation Planning | Design | Traffic Impact & Operations
11400 SE 8th Street, Suite 200, Bellevue, WA 98004 | Office (425) 889-6747
TECHNICAL MEMORANDUM DRAFT
DATE: May 2, 2022
TO: Marc Bargenda, Senior Project Manager
Federal Way Public Schools
FROM: Michael J. Read, PE, Principal
TENW
SUBJECT: Federal Way Public Schools – Illahee Middle School
Traffic Impact Analysis
TENW Project No. 2022-060
This memorandum summarizes a traffic impact analysis for the proposed renovation of Federal Way School
DistrictÊs Illahee Middle School located at 36001 1st Ave S in Federal Way, WA. This memorandum
includes a project description, a description of existing transportation conditions within the immediate site
vicinity, methodology used to derive the trip generation estimate, trip distribution, traffic operational analysis
of key off-site intersection and site driveway intersections under cumulative impacts, and identification of any
transportation mitigation measures to offset traffic impacts.
Project Description
Illahee Middle School is located at 36001 1st Ave S in Federal Way, WA. A project site vicinity map is
shown in Figure 1. For the purposes of this analysis, year 2025 was the horizon year assumed to evaluate
cumulative traffic impacts from the proposed renovation.
Illahee Middle School has an existing total gross floor area of approximately 109,000 square feet (per King
County parcel records) with an existing student enrollment of approximately 705 students and an existing
student capacity of 890 students. The proposed gross floor area of the new school would be approximately
106,000 square feet with a student capacity of up to 890 students. Therefore, the proposed renovation
would result in a net decrease of approximately 3,000 square feet of building area, a potential increase in
enrollment of up to 185 students, and no change to student capacity.
With the Illahee Middle School renovation project, access to a new student pick-up/drop-off loop and 8
visitor parking stalls would be provided on the East/West Private Road. Additionally, access to a new bus
loop with 39 staff parking stalls would be provided on 1st Ave S. The existing parking lot in the NE corner
of the school property would remain with the proposed project and would provide a total of 57 parking stalls
for staff and visitors. The parking lotÊs existing access on the East/West Private Road would remain but the
existing access on 1st Ave S would be removed. As part of the project, roadway frontage improvements
including sidewalks would be provided along 1st Ave S. A conceptual site plan of the project is illustrated
in Figure 2.
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 2
Figure 1 – Site Vicinity
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 3
Figure 2 – Site Plan
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 4
Existing Transportation Conditions
This section includes a description of the existing site, an inventory of existing roadway conditions, key
intersections in the site vicinity, existing daily and peak hour traffic volumes, intersection levels of service,
nonmotorized facilities and planned roadway improvements.
Existing Site
The existing Illahee Middle School was built in 1970 and includes a total of 109,000 square feet of building
area (per King County parcel records). Buses enter the one-way southeast-bound bus loop from the East/West
Private Road and exit on 1st Ave S. The existing bus loop also provides parking for staff along the north side
of the loop. Student drop-off/pick-up primarily occurs in side-by-side lanes within the existing staff/visitor
parking lot on the NE corner of the site. During both AM drop-off and Afternoon pick-up, vehicles enter the
parking lot from the East/West Private Road but during the Afternoon a staff member directs vehicles to enter
the parking lot from the driveway on 1st Ave S once the vehicle pick-up queue extends to the East/West
Private Road. During both the AM and Afternoon peaks, vehicles exit the parking lot via the driveway on 1st
Ave S. Secondary vehicular access to the site is provided by three additional driveways on 1st Ave S that
provide access to ADA and service parking stalls. Legal on-street parking is also available on both sides of
1st Ave S and on both sides of S 361st Place. An aerial image of the existing site is shown below.
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 5
Roadway Conditions
The following paragraphs describe existing arterial roadways that would be used for site access. Roadway
characteristics are described in terms of number of lanes, posted speed limits, pedestrian facilities, and
shoulder conditions.
S 356th Street is an east-west Minor Arterial located north of the Illahee Middle School site which provides
connection to SR 99 and I-5 towards the east. East of 1st Ave S, the roadway consists of 2 lanes (1 lane in
each direction) as well as approximately 5-foot paved shoulders and open ditches on both sides of the road.
No sidewalks are available on either side of the roadway east of 1st Ave S. West of 1st Ave S, the roadway
consists of 5 lanes (2 lanes in each direction plus a center turn-lane) as well as approximately 5-foot bike
lanes, curb and gutter, and 6-foot sidewalks on both sides of the road. The posted speed limit is 35 mph
east of 1st Ave S and 40 mph west of 1st Ave S.
1st Ave S is a north-south Minor Arterial located along the east side of the Illahee Middle School site which
provides connection to S 356th St towards the north. The roadway consists of 2 lanes (1 lane in each
direction) as well as approximately 5-foot paved shoulders on both sides of the road. Along the school
frontage, 6-foot sidewalks and street parking are available on both sides of the road. The posted speed limit
is 25 mph with a 20-mph flashing posted speed during school arrival and dismissal periods.
A vehicle speed survey was conducted over three days from March 8 to March 10, 2022 by Idax Data
Solutions on 1st Ave S just north of the East/West Private Road and also on 1st Ave S between S 361st Pl
and S 363rd Pl. Results of the speed survey are summarized below and the detailed speed study data is
included in Attachment B.
3-Day Average Speed (MPH)
1st Ave S north of
East/West Private Rd
1st Ave S between S 361st Pl
and S 363rd Pl
Percentile Northbound Southbound Northbound Southbound
50th Percentile 32.9 32.0 28.0 30.5
85th Percentile 39.1 38.9 35.2 37.2
95th Percentile 43.7 43.3 39.9 41.8
Traffic Study Intersections
To assess traffic impact of the proposed school renovation, the following study intersections were analyzed
during the weekday AM and afternoon peak hours:
1. 1st Ave S / SW 356th Street (signalized)
2. East/West Private Road / School Enter-Only Driveway (no control due to one-way (inbound)
southbound traffic flow)
3. East/West Private Road / School Parking Lot Driveway (no control, one-way southbound
(inbound) traffic flow)
4. 1st Ave S / East/West Private Road (stop-controlled)
5. 1st Ave S / School Parking Lot Driveway (stop-controlled)
6. 1st Ave S / S 361st Pl / School Exit-Only Driveway (stop-controlled)
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 6
Peak Hour Traffic Volumes
Year 2022 existing AM and afternoon peak hour traffic volumes at the study intersections were based on
counts conducted by Idax Data Solutions in March 2022. The AM peak hour traffic volumes represent the
highest hourly volume of vehicles passing through an intersection between 7:00 and 9:00 AM and the
Afternoon peak hour represents the highest hourly volume of vehicles passing through an intersection between
2:00 and 4:00 PM. As noted previously, based on information provided by the Federal Way Public Schools,
the existing student enrollment at Illahee Middle School at the time of the counts was 705 students.
Figure 3 and Figure 4 summarize the existing weekday AM and Afternoon peak hour volumes at the study
intersections. The March 2022 turning movement traffic counts at the study intersections are provided in
Attachment A.
Year 2022 existing weekday daily traffic volumes on 1st Ave S were also based on counts conducted by
Idax on Tuesday, March 8 through Thursday, March 10, 2022. North of the East/West Private Road, the
weekday average daily traffic (ADT) volume on 1st Ave S was 2,600. Between S 361st Place and S 363rd
Place the weekday ADT was 1,350. The ADT counts are provided in Attachment B.
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 7
Insert Figure 3 Existing AM Volumes
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 8
Insert Figure 4 Existing PM Volumes
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 9
Existing Intersection Levels of Service
An existing level of service (LOS) analysis was conducted at the six (6) study intersections. LOS generally
refers to the degree of congestion on a roadway or intersection. It is a measure of vehicle operating speed,
travel time, travel delays, and driving comfort. A letter scale from A to F generally describes intersection LOS.
At signalized intersections, LOS A represents free-flow conditions (motorists experience little or no delays), and
LOS F represents forced-flow conditions where motorists experience an average delay in excess of 80 seconds
per vehicle.
The LOS reported for signalized intersections, roundabouts, and all-way stop controlled intersections
represents the average control delay (sec/veh) and can be reported for the overall intersection, for each
approach, and for each lane group or movement (additional v/c ratio criteria apply to lane group or
movement LOS only). The LOS reported at two-way stop-controlled intersections is based on the average
control delay and can be reported for each controlled minor approach, controlled minor lane group, and
controlled major-street movement (additional v/c ratio criteria apply to lane group or movement LOS only).
Table 1 outlines the current HCM LOS criteria for signalized and unsignalized intersections based on these
methodologies.
Table 1
LOS Criteria for Signalized and Unsignalized Intersections1
SIGNALIZED INTERSECTIONS UNSIGNALIZED INTERSECTIONS
LOS by Volume-to
Capacity (V/C) Ratio2
LOS by Volume-to
Capacity (V/C) Ratio3
Control Delay
(sec/veh) £ 1.0 > 1.0
Control Delay
(sec/veh) £ 1.0 > 1.0
£ 10 A F £ 10 A F
> 10 to £ 20 B F > 10 to £ 15 B F
> 20 to £ 35 C F > 15 to £ 25 C F
> 35 to £ 55 D F > 25 to £ 35 D F
> 55 to £ 80 E F > 35 to £ 50 E F
> 80 F F > 50 F F
1 Source: Highway Capacity Manual (HCM), Transportation Research Board, 6th Edition, 2016.
2 For approach-based and intersection-wide assessments at signals, LOS is defined solely by control delay.
3 For two-way stop-controlled intersections, the LOS criteria apply to each lane on a given approach and to
each approach on the minor street. LOS is not calculated for major-street approaches or for the intersection
as a whole at two-way stop-controlled intersections. For approach-based and intersection-wide assessments
at all-way stop controlled intersections and roundabouts, LOS is solely defined by control delay.
Level of service calculations for intersections were based on methodology and procedures outlined in the 6th
Edition of the Highway Capacity Manual using Synchro 10 traffic analysis software.
The 2022 existing AM and Afternoon peak hour LOS analysis results for the study intersections are
summarized in Table 2. The LOS worksheets are included in Attachment C.
As shown in Table 2, the signalized intersection currently operates at LOS D or better and the individual
movements at the stop-controlled intersections all currently operate at LOS C or better under existing conditions
during the weekday AM and Afternoon peak hours.
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 10
Table 2
2022 Existing Peak Hour Level of Service Summary
2022 Existing
Study Intersection LOS
Delay
(sec)
V/C
Ratio
AM PEAK HOUR
Signalized Intersections
1. 1st Ave S / SW 356th Street C 22.0 --
Two-Way Stop-Controlled Intersections
2. East/West Private Rd / Enter-Only Driveway
Westbound Left-Turn A 7.7 0.05
3. East/West Private Rd / Parking Lot Dwy
Westbound Left-Turn A 7.6 0.16
4. 1st Ave S / East/West Private Road
Northbound Left-Turn A 8.8 0.01
Eastbound Approach C 15.9 0.01
5. 1st Ave S / Parking Lot Driveway
Northbound Left-Turn A 0.0 0.00
Southbound Left-Turn A 0.0 0.00
Eastbound Approach C 16.3 0.46
Westbound Approach A 9.5 0.00
6. 1st Ave S / S 361st Pl /Exit-Only Driveway
Southbound Left-Turn A 7.4 0.00
Eastbound Approach B 11.3 0.09
Westbound Approach A 9.3 0.03
AFTERNOON PEAK HOUR
Signalized Intersections
1. 1st Ave S / SW 356th Street C 21.2 -
Two-Way Stop-Controlled Intersections
2. East/West Private Rd / Enter-Only Driveway
Westbound Left-Turn A 8.0 0.02
3. East/West Private Rd / Parking Lot Dwy
Westbound Left-Turn A 7.3 0.03
4. 1st Ave S / East/West Private Road
Northbound Left-Turn A 8.2 0.01
Eastbound Approach B 14.0 0.03
5. 1st Ave S / Parking Lot Driveway
Northbound Left-Turn A 7.8 0.00
Southbound Left-Turn A 7.9 0.01
Eastbound Approach C 18.0 0.37
Westbound Approach B 10.0 0.01
6. 1st Ave S / S 361st Pl /Exit-Only Driveway
Southbound Left-Turn A 7.7 0.03
Eastbound Approach B 14.3 0.09
Westbound Approach A 9.8 0.07
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 11
Nonmotorized Facilities
Sidewalks or paved pedestrian pathways are located on both sides of 1st Ave S. Sidewalks are also located
along both sides of S 361st Place east of 1st Ave S. Marked crosswalks are located on all legs of the 1st
Ave S/S 356th Street intersection, and on the south and east legs of the 1st Ave S/S 361st Place intersection
directly adjacent to the school.
Planned Transportation Improvements
A review of the City of Federal WayÊs 2022-2027 Transportation Improvement Program showed that there
is one planned transportation improvement projects in the immediate study area.
· #26 – S 356th Street (1st Ave S to SR 99): Widen to 5 lanes with bike lanes and sidewalks
Traffic Impact Analysis
Based on information provided by Federal Way Public Schools, the proposed renovation of Illahee Middle
School will result in a total future student capacity of 890 students. The student capacity of the existing school
is also 890 students so the renovation project will result in no additional student capacity compared to existing
conditions. However, the student enrollment at Illahee Middle School at the time of the existing counts
conducted in March 2022 was 705 students. Therefore, the following section describes projected future
baseline traffic growth, distribution and assignment of new trips generated by full capacity of the school,
proposed changes to site access driveway configuration as a result of the new site plan, intersection level of
service, nonmotorized impacts, and identification of transportation mitigation to offset impacts.
Project Trip Generation
Per published trip generation rates within the Institute of Transportation Engineers (ITE) Trip Generation Manual,
11th Edition, 2021, for Land Use Code (LUC) 522 – Middle School/Junior High School, there is no
correlative basis to derive estimated changes in vehicle trip generation based on changes in floor area, but
better evidence of correlation on daily trips and significantly higher number of studies based on student
population. Based on TENW's extensive experience in reviewing K-12, private schools, and numerous
community colleges throughout the Pacific Northwest, the best correlative predictor of increase traffic demand
is student enrollment at school institutions.
To estimate the additional trips generated with the full capacity of Illahee Middle School (890 students), trip
generation associated with the net increase in student enrollment (890 student capacity less 705 existing
student enrollment = 185 net additional students) was calculated based on trip rates per student documented
in the ITE Trip Generation Manual, 11th Edition for LUC 522. The resulting new trip generation estimates
associated with a net increase in enrollment of 185 students are summarized in
Table 3 below. Detailed trip generation calculations are included in Attachment D.
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 12
Table 3
Trip Generation Summary
New Trips Generated
(+185 additional students)
Time Period In Out Total
Weekday Daily 194 194 388
Weekday AM Peak Hour 67 57 124
Weekday Afternoon Peak Hour 28 33 61
Weekday PM Peak Hour 13 15 28
As shown in Table 3, based on the net enrollment increase of 185 students, the net increase in vehicle trips
on a daily basis is estimated at 388 daily trips, with approximately 124 new trips generated during peak
arrival period (AM peak hour), 61 new trips generated during peak dismissal period (Afternoon peak hour),
and 28 new vehicle trips during the PM peak hour of adjacent street traffic.
Trip Distribution and Assignment
The distribution of new trips associated with the net increase in student enrollment (+185 students) to reflect
conditions with full student capacity (total of 890 students) at Illahee Middle School was based on existing
school boundary information and existing traffic volumes at the study intersections. Generally, distribution and
assignment of project trips were assumed as follows:
60 percent north on 1st Ave S
30 percent west on SW 356th Street
7 percent east on S 356th Street
3 percent south on 1st Ave S
Figure 5 and Figure 6 show the AM peak hour and afternoon peak hour new trip assignment at the study
intersections.
2025 No Action (Without Project) Traffic Volumes
Full buildout of the Illahee Middle School renovation project is anticipated by year 2025. Future year 2025
No Action (without project) AM and afternoon peak hour traffic volumes at the study intersections were
estimated by applying a 3 percent annual growth rate to the existing (2022) traffic volumes and adding the
new trips associated with the net increase in student enrollment to reflect full capacity of the existing school
(see Figures 5 and 6). It should be noted that annual growth was not applied to turning movements at the
Illahee Middle School existing site access driveways.
The resulting 2025 No Action (without project) traffic volumes at the study intersections are illustrated in Figure
7 for the AM peak hour and Figure 8 for the afternoon peak hour.
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 13
Insert Figure 5 AM Peak Hour Trip Assignment for additional 185 students
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 14
Insert Figure 6 PM Peak Hour Trip Assignment for additional 185 students
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 15
Insert Figure 7 2025 No Action AM Peak Hour Traffic Volumes
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 16
Insert Figure 8 2025 No Action PM Peak Hour Traffic Volumes
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 17
Site Access with New Site Plan
The following summarizes the proposed modifications to the study intersections and site access driveways
with the proposed renovation of Illahee Middle School:
1. 1st Ave S / SW 356th Street – no changes are proposed
2. East/West Private Road / School Drop-off/Pick-up Loop Driveway – this existing driveway will
provide entering and exiting access to the new drop-off/pick-up loop and visitor parking area.
3. East/West Private Road / School Parking Lot Driveway – this driveway to the parking lot for
staff and visitors will remain but would allow both entering and exiting movements with the
project.
4. 1st Ave S / East/West Private Road – this intersection is proposed to be converted to a compact
roundabout.
5. 1st Ave S / School Parking Lot Driveway – this driveway will be removed with the proposed
project.
6. 1st Ave S / S 361st Pl / School Bus Loop Driveway – this existing driveway will provide entering
and existing access to the new bus loop and staff parking area.
2025 With Project Traffic Volumes
Year 2025 No Action AM peak hour and Afternoon peak hour traffic volumes at the Illahee Middle School
site driveways were reassigned to reflect the new site access driveway configuration with the proposed
renovation project as described above. The anticipated shift in school traffic volumes as a result of the new
driveway configuration is summarized in Figure 9 for the AM peak hour and Figure 10 for the afternoon peak
hour. It should be noted that some of the movements shown in Figures 9 and 10 are negative which reflects
the anticipated change in travel patterns associated with the proposed new driveway operations in contrast
to existing conditions.
Year 2025 With Project peak hour traffic volumes were estimated by adding the shift in school trips associated
with the new site access driveway configuration (Figures 9 and 10) to the 2025 No Action traffic volumes
(Figures 7 and 8). The resulting future year 2025 With Project AM and afternoon peak hour traffic volumes
at the study intersections are shown in Figures 11 and 12.
Intersection Level of Service
A future year weekday peak hour Level of Service (LOS) analysis was conducted at the study intersections for
future year 2025 No Action (without project) conditions and future year 2025 conditions with the proposed
Illahee Middle School project. The roadway network assumed in the future year 2025 LOS analysis was
based on existing conditions as no planned improvements at the study intersections have been identified. It
should be noted that the 2025 No Action and 2025 With Project analyses both reflect a total student
enrollment of 890 students at Illahee Middle School (i.e., full capacity).
The weekday AM peak hour and Afternoon peak hour LOS results at the study intersections for 2025 No
Action (without project) and With Project conditions are summarized in Table 4. As shown, all study
intersections are projected to operate at LOS D or better with a v/c ratio under 1.0 during the AM and
afternoon peak hours in 2025 with the Illahee Middle School renovation project. Detailed LOS summary
worksheets are included in Attachment C.
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 18
Insert Figure 9 AM Peak Hour Volume Shift for New Driveway Configuration
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 19
Insert Figure 10 PM Peak Hour Volume Shift for New Driveway Configuration
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 20
Insert Figure 11 2025 With Project AM Peak Hour Traffic Volumes
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 21
Insert Figure 12 2025 With Project PM Peak Hour Traffic Volumes
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 22
Table 4
2025 Peak Hour Level of Service Summary
AM PEAK HOUR PM PEAK HOUR
Study Intersection LOS
Delay
(sec)
V/C
Ratio LOS
Delay
(sec)
V/C
Ratio
2025 NO ACTION
Signalized Intersections
1. 1st Ave S / SW 356th Street C 28.7 -- C 27.8 --
Two-Way Stop-Controlled Intersections
2. East/West Private Rd / Enter-Only Driveway
Westbound Left-Turn A 7.8 0.07 A 8.2 0.06
3. East/West Private Road / Parking Lot Driveway
Westbound Left-Turn A 7.8 0.21 A 7.3 0.06
4. 1st Ave S / East/West Private Rd
Northbound Left-Turn A 9.1 0.01 A 8.6 0.01
Eastbound Approach C 19.2 0.01 C 17.2 0.04
5. 1st Ave S / Parking Lot Driveway
Northbound Left-Turn A 0.0 0.00 A 7.9 0.00
Southbound Left-Turn A 0.0 0.00 A 8.0 0.01
Eastbound Approach C 24.5 0.67 E 37.1 0.72
Westbound Approach A 9.8 0.00 B 10.4 0.02
6. 1st Ave S / S 361st Pl /Exit-Only Driveway
Southbound Left-Turn A 7.5 0.00 A 7.7 0.03
Eastbound Approach B 11.8 0.13 C 16.6 0.18
Westbound Approach A 9.4 0.03 B 10.0 0.08
2025 WITH PROJECT
Signalized Intersections
1. 1st Ave S / SW 356th Street C 28.7 -- C 27.8 --
Roundabout Study Intersections
4. 1st Ave S / East/West Private Rd A 7.3 -- A 6.7 --
Two-Way Stop-Controlled Intersections
2. East/West Private Rd / Drop-off/Pick-Up Loop
Driveway
Northbound Approach B 10.8 0.43 A 9.8 0.31
Westbound Left-Turn A 8.2 0.32 A 7.7 0.17
3. East/West Private Rd / Parking Lot Driveway
Northbound Approach B 11.2 0.04 B 10.3 0.04
Westbound Left-Turn A 8.3 0.02 A 8.0 0.02
5. 1st Ave S / Staff & Visitor Parking Lot Driveway Removed with proposed project
6. 1st Ave S / S 361st Pl /Bus Loop Driveway
Northbound Left-Turn A 8.6 0.00 A 0.0 0.00
Southbound Left-Turn A 7.5 0.00 A 7.7 0.03
Eastbound Approach B 11.8 0.05 C 16.0 0.09
Westbound Approach A 9.4 0.03 A 9.9 0.07
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 23
Nonmotorized Impacts
As part of the proposed project, new sidewalks would be provided along the school property frontages on
1st Ave S.
Queuing Analysis at Student Pick-Up/Drop-Off Loading Areas
During traffic counts performed during peak arrival/dismissal periods, existing vehicle queuing was observed
by TENW staff related to parent drop-off/pick-up areas. The following paragraphs document existing and
future estimated site queuing that is generated by parent pick-up during peak dismissal periods.
Existing Site Queuing (Observed Full with Existing Student Load of 705 Students)
Within the on-site parking lot in the northeast corner of the site, existing parallel drop-off lanes provide 200
feet of queue storage or 400 feet total. In addition, a single-line queue out to the East/West Private Road
of 70 feet is provided and an interior drive aisle is also used (out to 1st Ave S) when the entering drive
becomes full with an additional 250 feet of storage. In summary, a total vehicle queue storage area of
approximately 720 feet is provided on site.
Forecasted Site Queuing (890 Students)
Based on existing enrollment, the future on-site queuing demand is estimated at 900 feet total, with a full
student load of 890 students. The proposed primary queuing area in the new drop-off/pick-up loop from the
East/West Private Road is approximately 650 feet. To achieve this length, an area of widening to allow for
vehicle queue through the eastern radius along with a continuous sidewalk would be needed. The
recommended secondary queuing area is within the redeveloped parking lot (250 feet) as this would provide
a safe walk route from the building into temporary parental queue area. The combined queue storage in the
primary drop-off/pick-up loop (650 feet) combined with the secondary queue storage in the parking lot would
result in a total of 900 feet of queue storage which would meet the estimated future queue demand.
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
TENW May 2, 2022
Page 24
Project Mitigation
A review of traffic impacts to intersection levels of service, site access, and circulation issues was conducted
in association with the proposed renovation of Illahee Middle Elementary School in Federal Way, WA. The
following mitigation measures are recommended to reduce or eliminate project impacts:
The City of Federal Way assesses a traffic impact fee rate of $3.00 per new square-foot of floor
area for middle schools (2018 Federal Way Impact Fee Components and Schedule). Based upon
a net decrease of 3,000 square feet (109,000 square feet existing and 106,000 square feet future),
no traffic impact fees would be required for the Illahee Middle School renovation project.
The applicant would be required to construct the necessary frontage improvements along 1st Ave S
which may include curb, gutter, sidewalk, and landscaping, which could also include right-of-way
donation.
The applicant would install a compact roundabout at the intersection of 1st Ave S / East/West
Private Road which will provide access to the new school drop-off/pick-up loop and the existing staff
and visitor parking lot.
It is recommended that a crossing guard be present at the intersection of 1st Ave S / East/West
Private Road during peak arrival and dismissal times to ensure that students can safely cross the west
leg of the intersection.
To address background vehicle speeding along 1st Ave S, the project is proposing to install raised
marked crosswalks at the intersections of S 361st Street and S 363rd Place.
If you have any questions regarding the information presented in this memo, please call me at (206) 361-
7333 x 101 or mikeread@tenw.com.
Attachments
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
ATTACHMENT A
Weekday AM and Afternoon Peak Hour Traffic Counts
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
ATTACHMENT B
Average Daily Traffic Counts and Speed Data
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
ATTACHMENT C
Intersection LOS Summary Sheets
Federal Way Public Schools – Illahee Middle School
36001 1st Ave South, Federal Way, WA
Traffic Impact Analysis
ATTACHMENT D
Trip Generation Calculations