Item 6C - Traffic StudyMEMORANDUM
To:Sandy Endy, P.E.
Development Engineer – City of Southlake
From: Douglas M Arnold, P.E.
Kimley-Horn and Associates, Inc.
Date: April 9, 2024
Re:Traffic Study for Willowtree Gardens / The Overlook
Proposed Residential and Office Development
Southlake, Texas
PURPOSE
This memorandum serves as a traffic study for a proposed single-family and office development located
on the west side of North Carroll Avenue, north of Southlake Boulevard, in the City of Southlake, Texas.
The development is anticipated to include 23 detached single-family dwelling units and 23,000 square
feet of general office space.Exhibit 1 (attached) provides the general site location of the proposed
development.
The following traffic assessment will include the following: existing and proposed roadway
characteristics, proposed development characteristics, need for auxiliary lanes, access spacing, sight
distance, and driveway intersection delay and level of service (LOS).
EXISTING TRANSPORTATION SYSTEM
North Carroll Avenue is a four-lane divided Arterial roadway with a posted speed of 30 mph. North
Carrol Avenue provides access for development traffic to Southlake Boulevard (FM 1709) to the south
and SH 114 to the north. Adjacent to the development, there is a raised median along North Carroll
Avenue. This section of North Carroll Avenue is built out to its ultimate cross section.
Southlake Boulevard (FM 1709) is a six-lane divided Arterial with a posted speed of 45 mph.
Southlake Boulevard provides access to Kimball Avenue and SH 114 to the east, and other City
thoroughfares to the west.
Based on recent (2019) TxDOT traffic count data, the daily volumes along North Carroll Avenue, north
of Southlake Boulevard, is approximately 19,900 vehicles per day. A peak hour traffic count was
performed during the weekday PM peak hour at North Carroll Avenue & Main Street on Tuesday,
February 20, 2024; based on this traffic count, the NB volume was 860 vehicles per hour and the SB
volume was 860 vehicles per hour. Exhibit 2 (attached) provides the weekday PM peak hour turning
movement counts at North Carroll Avenue & Main Street.
04/09/2024
Page 2
PROPOSED DEVELOPMENT INFORMATION
The proposed development sits on an undeveloped plot and as such generates no traffic. The
development’s concept plan (attached) includes 23 single-family detached housing dwellings and a +/-
23,000 square-foot general office building. A total of 5 of the 23 residential units are proposed to be
outside of the gated residential area with primary access via Cross Lane (that traffic will not access
North Carroll Avenue).
Site Access
As previously mentioned, the subject property is located on the west side of North Carroll Avenue. To
the north of the development, there is a developed residential neighborhood, and to the south is an
undeveloped parcel and an existing medical office building, both under separate ownership. West of
the subject property is a residential neighborhood; based on feedback from the neighborhood and the
Planning & Zoning committee; there will be no connections this development to that neighborhood via
Cross Lane. In the future, cross access will be provided to the adjacent properties.
Based on the development concept plan, there are two driveways proposed to serve the development.
The southern driveway, located approximately 600 feet north of Southlake Blvd, will primarily serve the
general office development. The northern driveway, located approximately 180 feet north of the
southern driveway and approximately 350 feet south of Ownby Ln, will primarily serve the homes.
Since there is a raised median along North Carroll Avenue spanning the entire frontage of the subject
property, the development is proposing to install a northbound left-turn lane to serve the northern site
driveway. An analysis of this proposed improvement will be provided later in the memo. The developer
is looking to get conceptual approval of the left-turn lane as part of this traffic study, with detailed
engineering plans to come as part of the site plan process. A photolog is provided as an attachment
that shows the line of sight for the proposed northbound left-turn lane; based on field observations,
minimum sight distance requirements are met.
Trip Generation
Based on trip generation fitted curve equations (higher than trip generation rates) from the 11th edition
of the ITE Trip Generation Manual for Single Family Detached Homes (ITE Land Use Code 210) and
General Office (ITE Land Use Code 710),the site is anticipated to generate 63 AM peak hour driveway
trips and 69 PM peak hour driveway trips. As noted above, the trip generation was calculated for 18
dwelling units since 5 of the units are proposed outside of the gated area and not access North Carroll
Avenue. A breakdown of the trip generation is provided in Table 1. No internal capture was assumed.
Table 1: Trip Generation Analysis
Trip Distribution and Assignment
It is anticipated that the site traffic will be distributed to North Carrol Avenue and Southlake Boulevard
accordingly: 30% to/from the west on Southlake Boulevard, 25% to/from the east on Southlake
Boulevard, 30% to/from the north on North Carrol Avenue, and 15% to/from the south on North Carroll
Avenue.
In Out Total In Out Total
Single-Family Detached Housing 210 18 Dwelling Units 208 4 12 16 12 8 20
General Office 710 23,000 SF 323 42 5 47 8 41 49
531 46 17 63 20 49 69TOTAL SITE TRAFFIC
Daily AM Peak Hour PM Peak HourLand Use Description ITE
Code
Intensity /
Units
Page 3
Exhibit 3 (attached) provides the anticipated trip distribution at the two (2) project driveways and one
(1) study intersection.Exhibit 4 (attached) provides the anticipated trip assignment at the driveways.
Exhibit 5 (attached) provides the anticipated total traffic volumes at the driveways, including both
current traffic along North Carroll Avenue (based on the weekday PM peak hour count at Nort Carroll
Avenue & Main Street) and the proposed site traffic. The traffic volumes in Exhibit 5 account for the
median modifications at Main Street.
Based on the trip assignment values, the increase in traffic along North Carroll Avenue as a result of
this proposed developments equates to less than a 2.0% increase between Southlake Boulevard and
the site and less than 1% north of the site.
DRIVEWAY CAPACITY ANALYSIS
A capacity analysis was performed for the project driveways along North Carroll Avenue. Capacity
analysis results are listed in terms vehicle delay and level of service (LOS). LOS is a qualitative term
describing operating conditions (vehicle delay) a driver will experience while traveling on a specific
street or highway during a specific time interval. It ranges from A (very little delay) to F (longer delays
and congestion). TxDOT considers LOS D or better to be the target LOS for design and evaluation
purposes. Average total delay ranges of each operational state for intersections, based on the Highway
Capacity Manual (HCM) 6th Edition, are presented in Table 2.
Table 2: Level of Service Definitions
Level of Service Signalized Intersection
Average Total Delay (sec/veh)
Unsignalized Intersection
Average Total Delay (sec/veh)
A ≤10 <10
B >10 and ≤20 >10 and <15
C >20 and ≤35 >15 and <25
D >35 and ≤55 >25 and <35
E >55 and ≤80 >35 and <50
F >80 >50
The capacity analysis was performed using Synchro, which is an intersection analysis software based
on the Highway Capacity Manual (HCM). The traffic volumes used for the analysis are the combination
of the PM peak hour volumes provided collected in February 2024 and the site traffic volumes from
Exhibit 2. As previously discussed, a northbound left-turn lane is proposed at the northern site
driveway. This analysis accounts for the redistribution of existing WB left-turning traffic from Main Street
that would make a WB right-turn movement and NB U-Turn movement at the proposed NB left-turn
lane as a result of the City’s proposed median modifications along North Carroll Avenue at Main Street.
Table 3 summarizes the intersection operation results for the three scenarios during the weekday AM
and PM peak hours. The delay and LOS were reported for the stop-controlled eastbound movement at
both driveways as well as the northbound left-turn movement at the northern driveways. Based on the
analysis, all movements are anticipated to operate at LOS C or better during both the AM and PM peak
hours. The Synchro 11TM output sheets for analyses are included as an Attachment.
Page 4
Table 3: Level of Service Summary
Due to the low number of right-turn volumes into the project driveways (+/- 7 vehicles during the AM
peak hour and +/- 3 vehicles during the PM peak hour at each driveway), right-turn deceleration lanes
are not recommended. The analysis further supports this as the southbound through movement is
anticipated to operate at LOS A at both project driveways during the AM and PM peak hours.
For the proposed NB left-turn lane, the anticipated 95th percentile queue during the PM peak hour is
less than one vehicle (+/- 25 feet) based on the Synchro analysis. A conceptual layout of the turn lane
is provided as an Attachment. The layout assumes a 75-foot taper and 75-feet of storage. If the City
desires to have a longer taper length, the design could be modified to show a 100-foot taper and 50-
feet of storage.
CONCLUSION AND RECOMMENDATIONS
A traffic study was performed for a residential and office development located on the west side of North
Carroll Avenue, north of Southlake Boulevard, in the City of Southlake, Texas.
The following conclusions can be made from the analysis:
· The development is anticipated to include 23 single-family dwelling units and 23,000 square
feet of general office space. Of the 23 residential units, 5 of them are proposed outside of the
gated neighborhood and built along Cross Lane. The development represents less than a 3.0%
increase in overall traffic volumes along North Carroll Avenue.
· The development is anticipated to have two driveways accessing North Carroll Avenue; the
northern driveway is anticipated to provide ingress and egress movements (left-turn egress
prohibited) and the southern driveway is anticipated to provide ingress and egress movements
(right-in and right-out only). The 5 residential units outside of the gated neighborhood will be
access via Cross Lane.
· In order to provide ingress from the south, which is anticipated to comprise of 70% of the total
entering site traffic, a northbound left-turn lane is proposed at the northern site driveway. The
left-turn lane would be designed similar to the existing southbound left-turn lane at Main Street,
which has a similar width median. The southbound queues at the intersection of Southlake
Boulevard & North Carroll Avenue are not anticipated to impact the proposed northbound left-
turn lane operations.
·All traffic movements at the driveway connections are anticipated to operate at LOS C or better
for during the PM peak hour. The northbound left-turn movement from the proposed left-turn
lane is anticipated to operate at LOS C with less than one vehicle queue during both the PM
peak hour.
Delay (sec/veh)LOS
EBR 12.0 B
NBL / NBU 16.2 C
North Carroll Avenue & Southern Driveway EBR 12.5 B
North Carroll Avenue & Northern Driveway
Intersection Movement PM Peak Hour
Page 5
EXHIBITS
LEGEND:
= Study Intersections
= Site Boundary
EXHIBIT 1
VICINITY MAP
WILLOWTREE GARDENS / THE OVERLOOK
Drive 1
Drive 2
East SouthlakeBoulevard
861
872
861
872
137
812 49 49
735 112
LEGEND:
X (Y)
X = AM Peak Hour Turning Movements
Y = PM Peak Hour Turning Movements
Volumes may not sum from point to point due to rounding
and presence of smaller driveways not included in analysis.
EXHIBIT 2
EXISTING (2024) TRAFFIC VOLUMES
N
NOT TO SCALE
WILLOWTREE GARDENS / THE OVERLOOK
E SOUTHLAKE BLVD NCARROLLAVESITE
MAIN STREET
15%15%
(50%)
70%(30%)
15% (50%)
(50%)
70%
(30%)
(70%) (30%)
70%
25%
(30%) (15%) (25%)
30%
15%
LEGEND:
X (Y)
X = AM Peak Hour Turning Movements
Y = PM Peak Hour Turning Movements
Volumes may not sum from point to point due to rounding
and presence of smaller driveways not included in analysis.
EXHIBIT 3
TRIP DISTRIBUTION
N
NOT TO SCALE
WILLOWTREE GARDENS / THE OVERLOOK
E SOUTHLAKE BLVD
SITE NCARROLLAVE30%25%
15%
30%
MAIN STREET
7 7
(3)(3)
9 (25)
32 5
(14)(15)
7 9
(3)(25)
37
(29)
9 (25)
12 0 5
(34)(0)(15)
32 0
(14)(0)
LEGEND:
X (Y)
X = AM Peak Hour Turning Movements
Y = PM Peak Hour Turning Movements
Volumes may not sum from point to point due to rounding
and presence of smaller driveways not included in analysis.
EXHIBIT 4
TRIP ASSIGNMENT
N
NOT TO SCALE
WILLOWTREE GARDENS / THE OVERLOOK
E SOUTHLAKE BLVD NCARROLLAVESITE
AM: 19 veh
PM: 21 veh
MAIN STREET
AM: 44 veh
PM: 48 veh
3 864
25 49 13 887
3 935
950
25
895 49 15 186
749 112
LEGEND:
X (Y)
X = AM Peak Hour Turning Movements
Y = PM Peak Hour Turning Movements
Volumes may not sum from point to point due to rounding
and presence of smaller driveways not included in analysis.
EXHIBIT 5
TOTAL TRAFFIC
N
NOT TO SCALE
WILLOWTREE GARDENS / THE OVERLOOK
E SOUTHLAKE BLVD NCARROLLAVESITE
MAIN STREET
4:00 PM 4:15 PM 4:30 PM 4:45 PM PHF
186 214 210 202 0.948598
PHF 4:45 PM 4:30 PM 4:15 PM 4:00 PM 8 15 16 10 0.765625
0.962042 188 182 191 174
0.777778 25 36 23 28
4:00 PM 10 25
4:15 PM 14 31
4:30 PM 12 33
4:45 PM 13 48
PHF 0.875 0.713542
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CONCEPTUAL SITE PLAN
Page 7
LEFT-TURN LANE CONCEPTUAL LAYOUT
Relocate exisitng monument
sign to north end of median.
Maintain 16-foot median. Include
a 2-foot median nose to prevent
prohibited turning movements.
Construct a median opening and
provide a 4-foot median nose.
Turn lane width +/- 10.5 feet.
Construct a hooded left-turn lane to serve
entry from the south into the development
at this proposed driveway connection.
75 Feet
of taper
75 Feet full
width lane
PROPOSED NORTHBOUND LEFT-TURN LANE
NORTH CARROLL AVENUE
SOUTHLAKE, TEXAS
Proposed Right-In / Right-out
Driveway Connection
North Carroll
Avenue
Existing southbound left-turn
lane to Main Street not impacted.
The
Container
Store
The Overlook /
Willowtree Gardens
Propsoed Development
Page 8
SYNCHRO REPORTS
HCM 6th TWSC Build-Out PM Peak Hour
1: N Carroll Ave. & Northern Driveway
Synchro 11 Report
Intersection
Int Delay, s/veh 0.7
Movement EBL EBR NBU NBL NBT SBT SBR
Lane Configurations
Traffic Vol, veh/h 0 25 49 13 887 864 3
Future Vol, veh/h 0 25 49 13 887 864 3
Conflicting Peds, #/hr 0 0 0 0 0 0 0
Sign Control Stop Stop Free Free Free Free Free
RT Channelized - None -- None - None
Storage Length -0 - 100 ---
Veh in Median Storage, # 0 ---0 0 -
Grade, %0 ---0 0 -
Peak Hour Factor 92 92 92 92 92 92 92
Heavy Vehicles, %2 2 2 2 2 2 2
Mvmt Flow 0 27 53 14 964 939 3
Major/Minor Minor2 Major1 Major2
Conflicting Flow All - 471 942 942 0 -0
Stage 1 -------
Stage 2 -------
Critical Hdwy - 6.94 6.44 4.14 ---
Critical Hdwy Stg 1 -------
Critical Hdwy Stg 2 -------
Follow-up Hdwy - 3.32 2.52 2.22 ---
Pot Cap-1 Maneuver 0 539 362 724 ---
Stage 1 0 ------
Stage 2 0 ------
Platoon blocked, %---
Mov Cap-1 Maneuver - 539 388 388 ---
Mov Cap-2 Maneuver -------
Stage 1 -------
Stage 2 -------
Approach EB NB SB
HCM Control Delay, s 12 1.1 0
HCM LOS B
Minor Lane/Major Mvmt NBL NBTEBLn1 SBT SBR
Capacity (veh/h)388 - 539 --
HCM Lane V/C Ratio 0.174 - 0.05 --
HCM Control Delay (s)16.2 - 12 --
HCM Lane LOS C -B --
HCM 95th %tile Q(veh)0.6 - 0.2 --
HCM 6th TWSC Build-Out PM Peak Hour
2: N Carroll Ave. & Southern Driveway
Synchro 11 Report
Intersection
Int Delay, s/veh 0.2
Movement EBL EBR NBL NBT SBT SBR
Lane Configurations
Traffic Vol, veh/h 0 25 0 950 935 3
Future Vol, veh/h 0 25 0 950 935 3
Conflicting Peds, #/hr 0 0 0 0 0 0
Sign Control Stop Stop Free Free Free Free
RT Channelized - None - None - None
Storage Length -0 ----
Veh in Median Storage, # 0 --0 0 -
Grade, %0 --0 0 -
Peak Hour Factor 92 92 92 92 92 92
Heavy Vehicles, %2 2 2 2 2 2
Mvmt Flow 0 27 0 1033 1016 3
Major/Minor Minor2 Major1 Major2
Conflicting Flow All - 510 -0 -0
Stage 1 ------
Stage 2 ------
Critical Hdwy - 6.94 ----
Critical Hdwy Stg 1 ------
Critical Hdwy Stg 2 ------
Follow-up Hdwy - 3.32 ----
Pot Cap-1 Maneuver 0 509 0 ---
Stage 1 0 -0 ---
Stage 2 0 -0 ---
Platoon blocked, %---
Mov Cap-1 Maneuver - 509 ----
Mov Cap-2 Maneuver ------
Stage 1 ------
Stage 2 ------
Approach EB NB SB
HCM Control Delay, s 12.5 0 0
HCM LOS B
Minor Lane/Major Mvmt NBTEBLn1 SBT SBR
Capacity (veh/h)- 509 --
HCM Lane V/C Ratio - 0.053 --
HCM Control Delay (s)- 12.5 --
HCM Lane LOS -B --
HCM 95th %tile Q(veh)- 0.2 --
Page 9
PHOTOLOG