Sandy Lk Cross L3-CS 890228~ Kimley-Horn and Associates, Inc. 12660 Coit Road, Suite 200, Dallas, Texas 75251 · (214) 386-7007
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February 28, 1989
Mr. Russell Doyle
City Engineer
City of Coppell
732 DeForest Road
Coppell, Texas 75019
Re: Restricted Left-Turn Access
Sandy Lake Crossing
Coppell, Texas
Dear Russell:
Per our discussion at our meeting on February 16, 1989, I am submitting this letter and the
attached sketch concerning the preliminary design concept for a restricted left-turn lane on
northbound Denton Tap Road between the existing median opening at Braewood Drive and the
opening into Minyards/McDonalds. This design restricts median access to northbound left-
turns from Denton Tap Road, serving a planned future driveway located in the vicinity of
Station 157 + 60 (+) on Denton Tap Road.
Kimley-Horn's transportation experts have reviewed the concept and determined that the median
access design provides the necessary transition and storage capacity to accommodate up to about
350 vehicles per hour, given unsignalized operations. Such unsignalized operation permits safe
and efficient ingress from arterials, particularly where the median access is located in close
proximity (1,000 feet or less) to a signalized intersection, i.e. Denton Tap at Sandy Lake. The
adjacent traffic signal operation will effectively create adequate gaps in the traffic stream
whereby ingress vehicles may safely negotiate the required turn maneuver.
Recommended standard design criteria for spacing of unsignalized access, published by the
Texas Transportation Institute, specifies a limiting distance of 250 feet separation for arterials
where the average running speed exceeds 35 mph. The proposed design satisfies this spacing
criteria. The other significant criteria is related to provision of adequate sight distance for left-
turn vehicles for running speeds exceeding 35 mph. The proposed left-turn lane provides for
the necessary sight distance.
Building client relationships since 1967
Mr. Russell Doyle
February 28, 1989
Page Two
We appreciate your assistance in the review' of this preliminary design as this left-turn is of very
significant importance to the proper development of the subject property. Please call if you have
any questions or comments.
Sincerely,
KIMLEY-HORN AND ASSOCIATES, INC.
~-,.
Aames M. Kurtz, P.E.
/ Project Manager
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