Serenity Ridge Condition #1THE CITY OF
DUB E
Masterpiece on the Mississippi
MEMORANDUM
June 20, 2007
TO: The Honorable Mayor and City Council Members
FROM: Michael C. Van Milligen, City Manager
SUBJECT: Serenity Ridge -Plaza Drive/Derby Grange Intersection
The Zoning Advisory Commission is recommending approval of the Preliminary Plat of
Serenity Ridge Subdivision with conditions. Staff has been advised that the developer,
John Herrig, is going to ask the City Council to remove condition #1, "Approval is
contingent upon resolution of the intersection improvements for Plaza Drive and Derby
Grange Road."
The City Engineering Department has had ongoing discussions with the developer,
John Herrig, Buesing & Associates (the engineering firm for the developer, John Herrig)
and HDR (an Omaha, Nebraska consulting firm) regarding the design criteria for the
proposed intersection of Plaza Drive at Derby Grange Road.
Based on the speeds and the current roadway design, Buesing & Associates evaluated
the existing vertical alignment of Derby Grange Road and determined the roadway
would have to be lowered up to 6.5 feet to meet the intersection design requirements for
an intersection in a 45-mph zone. The grading for this design was estimated at over
8,000 cubic yards, with 1,500 feet of roadway to be rebuilt. The approximate cost for
lowering the Derby Grange roadway in the vicinity of Plaza Drive is $375,000.
Based on the above analysis by Buesing & Associates and HDR, City Engineering
recommends that a design speed of 45 mph be established for intersection sight
distance for the proposed intersection of Derby Grange Road and Plaza Drive. This will
involve the regrading of the roadway or relocation of the intersection to meet the sight
distance requirements.
Recognizing that this is a collector street that connects a State of Iowa Highway (IA 32)
through a major shopping center (Asbury Plaza) (two things that also increase the value
of the development's lots) the City may want to consider some sharing in the costs of
this sight distance improvement. That could be determined through additional
discussions.
I concur with the staff recommendation and respectfully request that the Mayor and City
Council leave condition #1 as part of the Preliminary Plat approval.
~~
Michael C. Van Milligen
MCVM/jh
Attachment
cc: John Herrig
Barry Lindahl, City Attorney
Cindy Steinhauser, Assistant City Manager
Laura Carstens, Planning Services Manager
Gus Psihoyos, City Engineer
THE CITY OF
DUB E
Masterpiece on t)ze Mississippi
MEMORANDUM
June 19, 2007
FROM: Gus Psihoyos, City Engineer Q
-~~
TO: Michael C. Van Milligen, City Manager
SUBJECT: Serenity Ridge -Plaza Drive/Derby Grange Intersection
BACKGROUND
The City Engineering Department has had ongoing discussions with the
developer, John Herrig, Buesing & Associates (the engineering firm for the
developer, John Herrig) and HDR (an Omaha, Nebraska consulting firm)
regarding the design criteria for the proposed intersection of Plaza Drive at Derby
Grange Road. This memorandum outlines the issues associated with the
proposed intersection as shown in the submitted preliminary plat of Serenity
Ridge Subdivision.
DISCUSSION
The Engineering Department is concerned that the speed through this portion of
roadway appeared to be much higher than the posted speed of 35 mph. The
Engineering Department directed ECIA (East Central Intergovernmental Agency)
to conduct a traffic count/speed study on portions of Derby Grange Road at three
locations. The average current speed was found to be 44 mph for westbound
traffic and 45 mph for eastbound traffic near the proposed intersection of Plaza
Drive and Derby Grange Road. The 85th percentile was determined to be 52.72
mph for westbound traffic and 54.43 mph for eastbound traffic.
Based on the speeds and the current roadway design, Buesing & Associates
evaluated the existing vertical alignment of Derby Grange Road and determined
the roadway would have to be lowered up to 6.5 feet to meet the intersection
design requirements for an intersection in a 45-mph zone. The grading for this
design was estimated at over 8,000 cubic yards, with 1,500 feet of roadway to be
rebuilt. The approximate cost for lowering the Derby Grange roadway in the
vicinity of Plaza Drive is $375,000.
r
Another option of adding alert-turn lane at the proposed intersection was not
warranted by exiting traffic counts and would not sufficiently increase safety if the
sight distance issue was not resolved. Buesing & Associates recommended
traffic-calming devices such as flashing beacons, etc. to lower the speed of the
traffic near the proposed intersection.
City Engineering had additional discussions on the proposed intersection with
HDR. HDR agreed with the Engineering Department that the roadway should be
designed for 45 mph and recommended two options: 1) One option was to lower
the roadway to meet sight distance requirements for the proposed intersection.
2) The second option was to relocate the intersection across from Herod Lane.
(Relocating the intersection involves a third party not associated with the
proposed development.)
RECOMMENDATION
Based on the above analysis by Buesing & Associates and HDR, City
Engineering recommends that a design speed of 45 mph be established for
intersection sight distance for the proposed intersection of Derby Grange Road
and Plaza Drive. This will involve the regrading of the roadway or relocation of
the intersection to meet the sight distance requirements.
Another option was considered amulti-way stop sign at this location. HDR did
not recommend athree-way stop sign at this location because it would cause
driver confusion since it was not warranted based on the volume of traffic. They
felt a westbound driver would not expect a traffic control device at this location.
HDR also stated that "if a multi-way stop sign was installed, rumble strips and
flashing red lights should be considered for the Derby Grange Road traffic."
cc: Kyle Kritz, Associate Planner
Ron Turner, PLS
F:\USERS\Ischluet\GUS\MEMO\Serenity Ridge -Plaza Drive.Derby Grange Intersection.doc
Buesing & Associates
1212 Locust Street
Dubuque, IA 52001
Phone 556-4389
Fax 556-6717
Me111o1'anC~11111 Project No. 07118
To: Gus Psihoyos, Ron Tumer, Bob Schiesl, Kyle Kritz, Mike Fekierman & John Herrig
From: Tom Olthafer
CC: Ken Buesing
Date: Tuesday, May 18, 2007
Re: Plaza Drive/Derby Grange Intersection
ECIA conducted a traffic count/speed study on portions of Derby Grange Road at three
locations. Concern for a safe intersection (maintaining the existing traffic speed) has
prompted a discussion of geometric design improvements to Derby Grange Road.
Adherence to a selected improvement has, up to this time, been a prerequisite to the
approval of John Herrig's preliminary plat of Serenity Ridge Subdivision and the extension
of Plaza Drive. The following is a summary of the traffic speed study.
Loption
WB near
JFK EB near
JFK WB near future
Plaza Drive EB near future
Plaza Drive WB near
Hales Mill Rd EB near
Hales Mill Rd
AADT 573 628 361 410 286 363
Peak Volume 13 15 5 5 4 4
Av . S eed 47 50 44 45 42 46
Posted S ed Limit 45 45 35 35 35 35
Exceeding Posted
S eed 64.2 77.0 83.7 83.2 87.3 95.6
Exceeding
55 m h 11.1 21.8 8.94 12.60 2.05 6.74
85 Percentile
m h 53.87 57.96 52.72 54.43 48.43 52.00
Cars 98.80 98.40 98.10 97.60 98.30 97.60
Small Trucks 1.00 1.20 1.90 1.20 1.40 1.90
TrucksBusses 0.20 0.30 0.00 0.70 0.00 0.30
Two design options were ident~ed in a meeting on Monday, May 7, 2007;
• 1) Re-grading the vertical curve on Derby Grange to increase the sight distance
and,
• 2) Construct a left turn lane/passing lane for the entrance onto Plaza Drive.
The existing conditions of Derby Grange Road, when classed as a rural road, meet
the design requirements of a 40 mph design speed. The intersection sight distance is
deficit by 13 feet. More design criteria become non-compliant when a 45 mph design
speed is considered.
G:\07\118\doc107118-02memo.doc
Project Memorandum, Page 2
Existing Conditions:
Grades 10.10% & 4.39%
K = 63.48
Vertical curve length = 920 feet
Stopping sight distance = 370 feet
Intersection sight distance = 422 feet
Decision sight distance = 422 feet
Design Speed Conditions:
40 mph
8 % max
44
(determinE
305/336*
445
363*/660*
45 mph
6%max
61
:d by K value)
360/396*
500
435*/743~`
* adjusted for approach grade
Decision sight distance A/C
Avoidance maneuver A: stop on rural road
Avoidance maneuver C: speed/path direction change on rural road
Intersection sight distance is not adjusted for grade per AASHTO,.Exhibit 9-55.
Design Intersection Sight Distance -Case B1 -Left Tum from Stop.
Prior to proceeding with an in-depth study of the options, a preliminary profile was
evaluated to approximate the cut necessary to achieve the design goals of a 45mph
design speed. To achieve an intersection sight distance of 500 feet, Derby Grange
would require increasing the present 920 foot vertical curve to 1,300 feet and cuts up to
7 feet. The grade at Herod Lane would need to be lowered almost 4 feet and the grade
at the Plaza Drive intersection would lower over 6 feet. Additional grading of Herod
Lane would be required to achieve an acceptable approach grade. Wrthout doing any
further design, it became obvious that this option would be extremely cost ineffective.
Plan and profile sheets showing existing and potential curves are attached.
Widening of Derby Grange at the Plaza Drive intersection for a left tum lane is also an
ineffective solution. Existing traffic volumes do not warrant a left tum lane. See
AASHTO Exhibit 9-75.Guide for Left Tum Lanes on Two-lane Highways.
An alternative to a left turn lane is a Tee Intersection Bypass Lane typically used by the
Wisconsin DOT. The bypass lane allows a through vehicle to bypass cleft-turning
vehicle that is stopped in the traffic lane. An intersection that redirects the through traffic
brings in-to-play additional avoidance maneuvers that require increased sight distance.
In-effect, a turn lane or a bypass lane would also require re-grading the vertical curve
mentioned above.
According to SUDAS urban design criteria, Derby Grange Road could be classed as a
two lane minor arterial or a major collector (granting a variance for grades). Design
criteria does not warrant geometric improvements to the roadway. The advanced traffic
speed of the 85th percentile is not an indicator to increase the design speed, but rather
an indicator of the necessity of suitable traffic control devices to achieve a safe vehicle
speed. Designing a segment of the roadway with a greater design speed will only
promote increased traffic speed and a greater danger at other points along Derby
Grange.
f Project Memorandum, Page 3
Traffic volumes, vertical gradients, horizontal and vertical curves, one-lane bridges, and
density of access points all dictate the need for a slower traffic speed and solutions that
are economically feasible.
Summary:
• A traffic study that reports an 85th percentile traffic speed of over 50 mph on a
roadway presently posted at 35 mph has prompted the consideration of
measures that would provide a safer intersection.
• Re-grading the vertical curve on Derby Grange Road to achieve a 500 foot sight
distance would lower the Plaza Drive intersection about 6.5' and the Herod Lane
intersection about 4.0'. Excavation of over 8,000 cubic yard of earth, and 1,500
linear feet of pavement would be cost prohibitive.
• Construction of a left tum lane or a tee intersection bypass lane is;
o Not warranted by existing traffic volumes
o Would not increase safety unless sight distance was also increased
• Geometric improvements to meet the requirements of faster design speed at the
Plaza Drive Intersection increases the danger at other conflict points on Derby
Grange Road.
• Traffic calming and control devices would increase the safety at all points on
Derby Grange Road.
Recommendations:
Serious consideration should be given to the use of suitable traffic control
devices to lower the 85th percentile traffic speed.
The city of Dubuque and Dubuque County develop a cooperative agreement to
initiate and implement a uniform traffic control policy.
Traffic control devices could include:
o high visibility advanced waming signs
o flashing beacons (such as those used in school zones)
o Speed Zone Ahead and/or Reduced Speed Ahead signs
o Intersection signs in combination with name of side road
o Radar operated speed displays (mobile or mounted)
o Converging chevron pavement marking
References:
SUDAS Chapter 5: Roadway Design
AASHTO Chapter 3, Decision Sight Distance, Exhibit 3-3
AASHTO Chapter 9, Intersection Contrr~l, Exhibit 9-55, Exhibit 9-75
ATSSA: Low Cost Local Road Safety Solutions
ONE COMPANY
Many Solutions'" Memo
To~ Gus Psihoyos, P.E. City of Dubuque
From: Chris Malmberg, P.E. Protect:
William Sharp, P.E.
cc:
Date: 5/29/07 Job No:
RE: Derby Grange Road /Plaza Drive Intersection
Per request from the City, an independent review was conducted for the proposed intersection at Derby
Grange Road and Plaza Drive. The City provided background information, including a memorandum from
Buesing & Associates (dated May 18, 2007), with several attachments including the existing plan and profile
of Derby Grange Road. The City noted concerns with intersection sight distance of the proposed intersection,
considering the observed 85th percentile speed on Derby Grange Road of 53 MPH to 54 MPH.
HDR reestablished the existing vertical geometry provided by the City to evaluate the
sight distance that would be provided assuming no vertical improvements on Derby Grange Road. The
existing sight distances are noted below.
Existing Conditions at the Proposed Plaza Drive Intersection with Derby Grange Road -
• Derby Grange Road Stopping Sight Distance - 370'
• Plaza Drive Intersection Sight Distance - 420'
• Derby Grange Road Decision Sight Distance - 370' (note -Buesing & Associates Memo reported
422' for decision sight distance. Per the 2004, AASHTO Green Book, the eye height is 3.5' and the
object height is 2.0' for stopping and decision sight distance.)
Based on the existing Derby Grange Road horizontal and vertical alignment information provided, it appears
that the existing design provides a 45 mph design speed.
Traffic Projections
As part of this review, we were not provided the opportunity to review the proposed traffic projections for this
development. One thing that should be considered is that the proposed Plaza Drive intersection on Derby
Grange Road has the high potential to change the traffic patterns on Derby Grange Road. Plaza Drive will
create scut-through location for Derby Grange Road traffic from the west that want to access the Northwest
Arterial. This potential cut-though traffic should be considered in the capacity analysis.
Speed Limit
Considering the large difference between the posted speed limit and the design speed, we would suggest
follow-up with the Dubuque County Engineer. The posted speed limit is puzzling given the horizontal and
vertical geometry provided on Derby Grange Road and given that this is a rural undeveloped area. The actual
85 percentile speed is well above the design speed of Derby Grange Road, and enhanced enforcement or
traffic calming measures should be considered in this area.
Proposed Intersection Location - No Derby Grange Road Improvements
The proposed location of the Plaza Drive intersection is west of a substantial crest vertical curve, with an
instantaneous grade of 7.4% on Derby Grange Road. Due to the location of the intersection relative to the
vertical curve, a reduced design speed is provided unless the vertical alignment on Derby Grange Road is
improved. The available intersection sight distance is nearly adequate for 40 mph (15' less than criteria) and
the decision sight distance (for a stop on a rural road) for the proposed location provides a design speed of 40
mph.
Considering this will be a public street intersection, HDR is concerned about the intersection and decision
sight distance provided at the proposed intersection location. Our opinion is that the existing design speed on
HDR Engineering, Inc. 8404 Indian Hills Drive Phone (402) 399-1000 Page 1 of 2
Omaha, NE 68114-4098 I Fax (402) 399-4979
www.hdrinc.com
Derby Grange Road of 45 mph should be required for intersection sight distance at this new intersection.
Additionally, the intersection would be located on a 7.4% grade, effecting acceleration /deceleration and
wintertime operations. Noted below are several design options that can be considered to mitigate some or all
these concerns.
Design Option 1 -Derby Grange Road Vertical Alignment Improvements
As noted in the Buesing & Associates Memo, an option was investigated to improve the intersection and
decision sight distance on Derby Grange Road by increasing the vertical curve length from 900' to 1320'. This
design option would meet a 45 mph design speed for intersection and stopping sight distance, and flatten the
grade at this intersection. In our opinion, this would be a viable option because it provides fora 45 mph
design speed.
Design Option 2 -Provide the Proposed Plaza Drive Intersection at Herod Lane
This option would provide a proposed intersection opposite Herod Lane. This location is near the crest of the
existing Derby Grange Road vertical curve, improving visibility for all legs of the intersection. This location
would provide a 45 mph intersection sight distance without modifications to the existing geometry, and would
eliminate the 500' offset intersections in Design Option 1. We understand the developer does not own the
property south of Herod Lane. With this option, we would recommend the developer build a portion of Plaza
Drive that would be compatible with a future connection across from Herod Drive. This connection would be
planned in the future as the area to the east develops. With this option, no access to Derby Grange Road
would be provided with the proposed development.
Design Option 3 -Addition of a Derby Grange Road Left-Turn /Bypass Lane
As noted in the Buesing & Associates Memo, an option was also investigated to provide alert-turn lane and
bypass lane on Derby Grange Road. As noted by Buesing & Associates, the projected left-turn volume at this
intersection would not warrant alert-turn lane (per AASHTO Exhibit 9-75).
Our opinion is that the left-turn lane would help mitigate the lack of decision sight distance for westbound
traffic. However, this option would not mitigate the substandard intersection sight distance for northbound
Plaza Drive traffic turning left onto Derby Grange Road.
Summary
In summary, it is our opinion that the intersection sight distance provided for the proposed intersection should
provide for a design speed of 45 mph (similar to existing conditions). Design Options 1 and 2 would fully meet
this criteria.
HDR Engineering, Inc. 8404 Indian Hills Drive Phone (402) 399-1000 Page 2 of 2
Omaha, NE 681144098 Fax (402) 399-4979
www.hdrinc.com
AREA ROADS AND SPEED LIMITS
(CLOSEST PROXIMITY ROADS TO DERBY GRANGE RD)
DERBY GRANGE RD.-OFF JFK -FIRST 1/2 MILE =~SMPH THEN DROPS TO 35 MPH
1. JOHN F. KENNEDY RD/NW ARTERIAL DOWN TO HWY 52 - 30 AND 35 MPH
2. CLAY HILL RD - 3~ MPH
3. RUPP HOLLOW RD.- 3S MPH
4. BURTON FURNACE RD - 5 DOWN TO 30 MPH
5. HALES MILL RD TO ASBURY RD- 3.5 MPH
6. LORE MOUND RD - .35 MPH
7. SEIPPEL RD - 35 MPH
8. HEACOCK RD - 3S MPH
9. MIDDLE RD - 35 MPH
10. RADFORD RD - 3=+ MPH
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