Blackberry Farm-SY130206 rill 3030 LBJ FREEWAY-SUITE 1660
DALLAS,TEXAS 75234
972/248-3006 FAX 972/248-3855
TOLL FREE 888/298/3006
LEE cnemEERInc
February 6, 2013
Mr. Terry Holmes
The Holmes Builders
225 E Hwy 121, Suite 120
Coppell, TX 75019 ,
Re: Visibility Study—Blackberry Farm Development on Sandy Lake Road
The City of Coppell has requested that a visibility study be performed at the proposed access
location for the Blackberry Farm development on Sandy Lake Road. This report summarizes the
results of the traffic analysis conducted for this intersection. The study focuses on documenting
existing conditions and providing alternatives to address safety concerns at the intersection.
Existing Conditions
Sandy Lake Road is a four-lane divided roadway with a posted speed limit of 40 mph in the
vicinity of the subject intersection. Sandy Lake Road is defined as a`Boulevard"by the Coppell
2030 Thoroughfare Plan. Blackberry Drive will be a four-lane divided roadway at the
intersection with an assumed posted speed limit of 30 mph and is currently stubbed out. A
vicinity map of the study area is shown Figure 1. The proposed Blackberry Farm site plan is
shown in Figure 2.
Figure 1: Vicinity Map
Study
Intersection
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Sight Distance Blackberry Farm
February 2013
Proposed Development
The proposed Blackberry Farm development is planned to consist of 82 single family homes.
The number of trips generated by the development is a function of the type and quantity of land
use for the development. The number of vehicle trips generated by the proposed development
was estimated based on the trip generation rates and equations provided in the publication
entitled Trip Generation Manual, Ninth Edition, by the Institute of Transportation Engineers
(ITE). Estimates of the number of trips generated by the site were made for the AM and PM
peak hour, as well as on a daily basis. The trip generation rates and the directional splits for this
development are shown in Tables 1 and 2. Table 3 presents the number of trips generated by
the proposed development at build-out.
Table 1: Trip Generation Rates for Proposed Blackberry Farm Development
Land Use Rates'
Description ITE Code Average Weekday AM Peak Hour PM Peak Hour
Single Family 210 0.92*Ln(X)+2.72 T=0.70X+9.74 0.90*Ln(X)+0.51
IT=Trips Ends;X=Dwelling Units
Table 2: Directional Splits for Proposed Blackberry Farm Development
Land Use Directional Split'
Description ITE Code Average Weekday AM Peak Hour PM Peak Hour
Single Family 210 50/50 25/75 63/37
'XX/YY=%entering vehicles/%exiting vehicles
Table 3: Estimated Trip Generation for Proposed Blackberry Farm Development QT 993 Travel Center
1 Average Weekday AM Peak Hour PM Peak Hour
Land Use Variable
Total In Out Total In Out Total In Out
Service Station with 82 876 438 438 68 17 51 88 55 33
Convenience Market
'Dwelling Units
Intersection Sight Distance
As part of this traffic analysis, the available and required intersection sight distance for motorists
accessing the adjacent roadways from Blackberry Drive was analyzed. The sight distance
required was estimated using the procedures developed by the American Association of State
Highway and Transportation Officials (AASHTO) and published in the 2011 edition of A Policy
on Geometric Design of Highways and Streets. At these locations,the motorist should be able to
see if and when adequate gaps exist to perform their desired maneuver. Table 4 presents the
required and available sight distance for vehicles at Blackberry Drive.
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Sight Distance Blackberry Farm
February 2013
Table 4: Sight Distance Evaluation
Major Roadway Sandy Lake Road
Speed 40 mph
Minor Roadway Blackberry Drive
Design Vehicle Passenger Car
Required Intersection Sight Distance 530'
(Exiting Movements at Driveways)
Required Intersection Sight Distance 355'
(Entering Movements—EB LT)
Available Sight Distance to the Left >1,500'
(SB Exiting Movement)
Available Sight Distance to the Right >1,500'
(SB Exiting Movement)
Available Sight Distance to the East 145'
(EB LT Entering Movement)
Sight Distance Available>Required
To the Left YES
To the Right YES
To the East NO
Comparing the field investigation results of the available sight distance to the required sight
distance values indicates that adequate sight distance will be provided for passenger cars exiting
the development. The existing sight visibility conditions looking west (Figure 3) and looking
east (Figure 4) exceed the minimum required. However, the sight distance for cars entering the
site from the eastbound left turn lane on Sandy Lake Road (145') does not meet the minimum
requirements (355').
The existing intersection sight distance on Sandy Lake Road varies from 145 feet to greater than
1,200 feet. The variability in sight distance is due to the existing landscaping within the median.
From a sitting position inside a vehicle, a driver can see 145 feet (Figure 5). The reduced
visibility is a direct result of the existing landscaping within the median (Figure 6). Median
landscaping provides a visual obstruction and can serve as traffic calming. However, within
sight lines, the landscaping should be kept below 30 inches from the roadway surface to above
seven feet (7'). Based on the existing conditions, if the existing landscaping was removed and
replaced with landscaping that provided a clear sight line, adequate intersection sight distance
would be provided.
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Sight Distance Blackberry Farm
February 2013
Figure 3: View from Blackberry Drive looking West(to the right)
Figure 4:View from Blackberry Drive looking East(to the left)
aims
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Sight Distance Blackberry Farm
February 2013
Figure 5: View from Eastbound Left Turn Lane on Sandy Lake Road looking East
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Figure 6: Existing Median Landscaping
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Sight Distance Blackberry Farm
February 2013
Conclusions
• The available sight distance for southbound passenger vehicles on Blackberry Drive to
turn left (1,500 feet) and right (1,500 feet) onto Sandy Lake Road exceeds the minimum
required sight distance(530 feet).
• Under existing conditions, the available sight distance for eastbound left turn vehicles on
Sandy Lake Road to turn left onto Blackberry Drive (145 feet) does not meet the
minimum required sight distance (355 feet). If the existing median landscaping is
replaced with landscaping that maintains the "clear zone", adequate intersection sight
distance will be provided for this movement.
If you have any questions regarding this study, please contact me at (972) 248-3006. We
appreciate the opportunity to provide these services.
Sincerely,
2--
Kelly .Parma,P.E.,PTOE
Senior Project Manager
Lee Engineering,LLC
TBPE Firm F-450
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