ST9304-CS 950510DALLAS COUNTY
PUBLIC WORKS
May 10, 1995
Mr. Ken Griffin, P.E.
Assistant City Manager/City Engineer
City of Coppell
P O Box 478
255 Parkway Boulevard
Coppell, TX 75019
Re:
Belt Line Road -- Project No. 490-403.1 / 91-829
(Denton Tap Road to Mac Arthur Boulevard)
Intersection Geometry
Dear Mr. Griffin:
As we discussed May 10, 1995, there are several outstanding issues regarding the intersections
along Belt Line Road. Attached is a letter and several pictures from Halff Associates, Inc. of
the proposed intersections of Belt Line Road with MacArthur Boulevard, Mockingbird Lane and
Moore Road. The County recommends that, as long as safety is not compromised, every effort
be made to avoid altering the railroad crossings. If the City of Coppell utilizes free right turn
lane standards that differ from the AASHTO standards, the County will see that those City
standards are used in the design. As discussed in the pre-design meeting, all construction costs
associated with the auxiliary lanes (e.g., free right turn lanes) are to be paid by the City.
Dallas County does not agree with Halff Associates' assertion that these intersection details are
outside the scope of their contract. Their contract is for the complete design of Belt Line Road
and does not preclude the intersections. The County will relate this position, along with your
decisions regarding the intersections' geometry, to Halff Associates upon reciept of Coppell's
response. Please forward your comments regarding the intersections by May 22, 1995. You
may contact me at 653-7151 if you have any questions concerning this project.
Sincerely,
11 h.
t Engineer
Attachments
ABB\ABR\JMS
6.0829XINTER S. LTR
411 Elm Street Dallas, Texas 75202 653-7151
Dallas County Public Works
411 Elm Street
Dallas. Texas 75202
May 4. 1995
AVO 14111
Attn: Ms. Jill M. Schneberger, P.E.
Project Engineer
Re:
Project 490-403.1/91-829
Dear Ms. Schneberger:
As part of the design process, Halff Associates has evaluated the cometry of the
MacArthur Boulevard, Mockingbird Lane and Moore Road and d
Grapevine Creek Bridge. Please find enclosed sketches of the three intersections with the
proposed right turn lane.
Our current geometry for the right turn lanes is based on AASHTO Design
Classification 'B' which is defined as providing for SU vehicles and permits occasional
WB-50 vehicles to turn with slight encroachment on adjacent traffic lanes. Observations
regarding impact on the existing railroad crossings are as follows:
The flee right from westbound Beltline Road onto northbound Moore Road
contains a 115 degree turn. The corresponding AASHTO radii for Design
Classification 'B' are 100, 30, and 100 feet for a three center curve, with a 5-foot
offset. The face-to-face dimension between the island and inside curb should be
24 feet. Modifications to the railroad ,crossing should not be required for this
geometry.
2. The flee right turn from westbound Beltline Road onto northbound Mockingbird
Lane will have the same geometry as discussed in Item No. 1 above. Such a
design will require extension of the existing railroad crossing approximately 2 feet
4~ \~- to the east. A simple curve with a 70-foot radius .would also encroach upon the
crossing. Railroad crossing modifications could be avoided by using a simple
curve radius of 60 'feet for the inside curb. However, this would reduce the
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Dallas County Public Works
May 4. 1995
Page 2
capacity to AASHTO Design Classification 'A' which is defined as providing
primarily for passenger vehicles while permitting occasional SU vehicles to turn
with restricted clearances.
The free right turn lane from westbound Beltline Road onto northbound
MacArthur Boulevard is 11 feet wide with an 18-foot (face-to-face) dimension
between the island and inside curb lines. The inside curb through the turn is a
three centered compound curve with radii of 150. 50. and 150 feet and an offset
of 5 feet. The point of tangency of these curves will be approximately 25 t~et
north of the existing railroad tracks. As a result. extending the railroad crossing
approximately 4 feet to the east will be required. An equivalent 70-foot simple
radius curve will also encroach onto the railroad crossing. Either scenario will
require relocation of the existing crossing gates and signals. Reducing the capacity
to AASHTO Design Classified in 'A' was also explored. The design would also
require an extension of the railroad crossing and relocation of the existing crossing
gates and signals. The only design which would eliminate these impacts would
be to eliminate the proposed free right turn lane.
Moore Road and Mockingbird Lane represent intersections of 2-lane collector
streets with a major arterial road. As such, AASHTO Classification 'B' turn lanes would
be desirable if free right turn lanes are provided. The intersection at MacArthur
Boulevard contains two major arterial roadways. If free right turn lanes are provided, it
is our opinion that an AASHTO Design Classification 'B' turn lane should be cons'idered
as a minimum standard at this location. Please provide Halff Associates with direction
regarding the geometry of these right turn lanes. Please be advised that neither the right
turn lanes nor railroad crossing modifications were included in the original construction
estimate or engineering services proposal. Additionally, the right turn lanes may impact
the right-of-way agreements with DART. If the design and coordination of railroad
crossing modifications are required, additional engineering fees would be required. We
are proceeding with the preliminary design for the project; however, the right turn lane
geometry cannot be finalized until this issue is resolved.
51 'R\'IC~'< )RS
Dallas County Public Works
May 4. 1995
Page 3
At this time, we would like to confirm our direction regarding channel grading at
the proposed Grapevine Creek bridge. We have developed grading plans which extend
only far enough upstream and downstream to tie into the existing channel, No attempt
has been made to provide channelization between the proposed bridge and the existing
railroad trestle to the north. Please advise us if this approach is incorrect.
TJK/kdh
Enclosure
Please call if you have any questions or require additional information.
Yours very truly,
HALFF ASSOCIATES, INC.
Thomas J. Kni
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