Item 7B - Lee Engineering TIA Review #1 - 08-13-202171prac
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August 13, 2021
Sandy Endy, P.E.
Development Engineer
City of Southlake
1400 Main Street, Suite 320
Southlake, Texas 76092
Re: Drive -Through Queue Study, NW Corner of Southlake & White Chapel — Review #1
Dear Ms. Endy:
ARIZONA
TEXAS
NEW MEXICO
OKLAHOMA
Per your request, we have completed a review of the study conducted for the proposed redevelopment on the
northwest corner of the intersection of FM 1709 (Southlake Boulevard) and White Chapel Boulevard in Southlake,
Texas. The study titled "Drive -Through Queue Analysis, NW Corner of Southlake & White Chapel, Southlake,
Texas" was prepared by Traffic Impact Group, LLC, and dated June 9, 2021. The site plan shown in the study was
dated June 2, 2021. An updated site plan received by LEE was dated June 28, 2021.
Comments are numbered for ease of reference and the numbering does not imply any ranking. We have divided
our comments into two categories — Informational Comments are those that require no action by the City or the
applicant. Action Comments are those that require a response or action by the City or applicant. We offer the
following comments on the submitted study.
INFORMATIONAL COMMENTS (REQUIRE NO ACTION BY CITY OR APPLICANT)
1. The study indicates that the redeveloped site will include a new 4,600 square foot building. Planned uses
within the building were assumed to be a 2,500 square foot retail site and a 2,100 square foot restaurant
with drive -through window. The study indicated that it was likely that the restaurant would be a coffee
shop, although no tenants are planned at this time.
2. The proposed redeveloped site will replace a gas station with convenience market and an automated car
wash. The existing gas station appears to include approximately 3,500 square feet of retail space and
10 vehicle fueling positions based on Google imagery. This lot is part of a larger site which includes a
grocery store (63,959 SF) and retail strip center (33,782 SF).
3. The proposed redeveloped retail/restaurant site will primarily utilize two (2) existing driveways, which are
part of the six existing driveways serving the entire site (3 on FM 1709 and 3 on White Chapel Boulevard).
4. Based on the latest site plan, the proposed redeveloped retail/restaurant site will have 37 parking spaces.
The remainder of the larger site will include 346 existing parking spaces, for a new total of 383 spaces.
5. The study calculates a total site trip generation estimate of 95 entering and 92 exiting trips during the AM
peak hour and 46 entering and 45 exiting trips during the PM peak hour assuming the 2,100 SF portion of
the building as a Coffee/Donut Shop with Drive -Through Window (ITE Land Use 937), which is consistent
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with the latest edition of the ITE Trip Generation Manual. Trip generation was not performed for the
2,500 SF retail portion of the building. The critical hour for the study was identified as the AM peak hour.
The predicted average queue from the pick-up window to the end of queue was 2.83 vehicles. The
predicted 95th percentile queue was eleven (11) vehicles. The study recommended that the site provide
storage for eleven vehicles between the pick-up window and the drive -through entrance.
a. Queue calculations appear to have been performed correctly, based on the assumptions utilized.
The newer site plan includes a different drive -through configuration compared to the site plan in the
traffic study. The eastern drive -aisle was moved to be closer to and parallel with White Chapel Boulevard,
and drive -through queue storage was increased from 9 to 11 vehicles. This includes room for five (5)
vehicles queued between the pick-up window and ordering station and six (6) vehicles queued between
the ordering station and drive -through entrance.
ACTION COMMENTS (REQUIRE RESPONSE OR ACTION BY CITY OR APPLICANT)
8. It should be noted that the scale shown in the newer site plan (dated June 28, 2021) appears to be
incorrect. The site plan appears to be shown at a 1:40 scale while the scale bar identifies a 1:50 scale.
Specific measurement values shown on the site plan appear to be the correct numbers.
The study assumed that half of the entering vehicles would use the drive -through and half would park,
based on the ITE pass -by rate of 49% in the AM peak hour for Fast -Food Restaurant with Drive -Through
Window (ITE Land Use 934). Therefore, the assumed arrival rate was 47 vehicles per hour.
a. It is unclear why pass -by percentage was utilized to estimate the number of vehicles entering the
drive -through, as the two do not appear to be related.
b. Based on experience, we believe it likely that a higher percentage would enter the drive -through.
c. Please provide additional data or description supporting the assumption that only 50% of
entering traffic will utilize the drive -through.
10. The study assumed an average service time of one minute (60 seconds) for ordering and receiving an
order, based on the assumption that vehicles exit the drive -through and park for orders that take longer
than one minute.
a. It is unclear if vehicles would be expected to exit the drive -through to wait for coffee in this
manner based on observations of other coffee shops with drive -through windows. Similar
operation has been observed for fast-food restaurants, however.
11. Based on the above assumptions, it is unclear if the predicted average and 95th percentile queue lengths
are accurate.
12. The study does include any additional analysis elements. Based on the City of Southlake Driveway
Ordinance, "existing driveways that are not in conformance with this ordinance shall be brought into
compliance" if the existing driveway volume is projected to increase by 20% or more during the
design hour. For reference, estimated existing and proposed trip generation for the redeveloped site
is shown in the following table, along with the percent change.
a. Based on preliminary trip generation, it is likely that AM peak hour site traffic will increase with
the redevelopment. Trip generation should be provided comparing existing trips and projected
trips to determine whether traffic at each driveway is predicted to increase more than 20%.
b. Additionally, traffic may also increase at the southern driveway in general. Currently, this
driveway terminates at the existing automated car wash. With the redevelopment, this driveway
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will provide direct access to the rest of the shopping center. All three driveways on FM 1709 are
right-in/right-out and this is the first driveway encountered by drivers.
13. In general, existing driveway spacing does not meet requirements in the Driveway Ordinance, as identified
in the table below for reference. A variance may be required for both driveways.
To Adjacent Street
To Adjacent Driveway
Driveway
(Centerline to ROW)
(Centerline to Centerline)
Existing
Required
Meets?
Existing
Required
Meets?
Eastern driveway on
225'
200'
Yes
180,
250'
NO
White Chapel Blvd
Southern driveway on
19S'
500,
NO
144'
250"
NO
FM 1709
14. Additionally, based on the number of parking spaces for the entire site and the Driveway Ordinance,
100 feet of driveway storage length is required (measured from the property/ROW line to the first parking
spot or cross -movement).
Existing driveway storage for the eastern driveway on White Chapel Boulevard is 25 feet and it is
shown to increase to 55 feet in the latest site plan (June 18, 2021). However, a variance may be
required.
Existing driveway storage for the southern driveway on FM 1709 is 10 feet and is not anticipated
to change. A variance may be required.
The newer site plan results in a shorter driveway storage length for the eastern driveway on
White Chapel Boulevard compared to the site plan in the traffic study. The advantage of
additional queue storage should be weighted against the advantage of additional driveway
storage length.
15. Anticipated driveway volumes should be presented in order to identify if thresholds for consideration of
a right -turn lane are met.
Sincerely, ,r
Kristen Novak, P.E., PTOE
Project Engineer
Lee Engineering
TBPE Firm F-450
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