HomeMy WebLinkAboutJuly 11, 2014 info pktDubuque Street
Foster to Taft (After)
Parcel Lines
NEPA Boundary
Dubuque Street
Foster to Taft (Before)
Parcel Lines
NEPA Boundary
Dubuque Street
Taft to Terrell Mill (After)
Parcel Lines
NEPA Boundary
Dubuque Street
Taft to Terrell Mill (Before)
Parcel Lines
NEPA Boundary
Dubuque Street
Terrell Mill to Cliff
Apartments (After)
Parcel Lines
NEPA Boundary
Dubuque Street
Terrell Mill to Cliff
Apartments (Before)
Parcel Lines
NEPA Boundary
Dubuque Street
Cliff Apartments to
Mayfl ower (After)
Parcel Lines
NEPA Boundary
Dubuque Street
Cliff Apartments to
Mayfl ower (Before)
Parcel Lines
NEPA Boundary
Iowa City Gateway
Alignment Options for Iowa River Trail Along Dubuque Street
Page 1 of 2
Iowa City Gateway
Alignment Options for Iowa River Trail Along Dubuque Street
July 10, 2014
Staff is considering two options for the proposed design for the section of the Iowa River Trail that
follows along the west side of Dubuque Street between Kimball and Foster roads. Option A follows
parallel to the realigned Dubuque Street. Option B follows in parallel to Dubuque Street between
Foster Road and Taft Speedway and from Taft Speedway to the south follows the existing
alignment. For your reference, please find attached an exhibit displaying the proposed location for
each of the alignments.
Each option is based on the general requirements established by the American Association of State
and Highway Officials (AASHTO) Guide for the Development of Bicycle Facilities. Each has a
minimum trail design speed of 20mph. To provide safety for all users, a maximum safety distance
of 8-feet from the back of curb was established at street crossings to provide visual contact with
vehicles entering or exiting the driveway. Vertical alignment does not exceed a 6 percent grade to
provide users safety while passing or stopping.
In reviewing which option to implement, staff considered several factors. The factors include the
following:
• Vertical elevation in relation to the one hundred year floodplain,
• Constructability,
• Additional NEPA coordination,
Following below is a discussion on the potential benefits and drawbacks of each option.
Option A - Parallel Trail
As approved as part of the Preferred Alternative during the NEPA process, this section of the Iowa
River Trail was designed to run parallel to the west side of Dubuque Street at a standard offset from
the back of curb. This provides simplicity during design and construction as well as meeting user
expectation of following the path of the roadway. The width of the Iowa River Trail in this section is
10 feet, and like Dubuque Street, the minimum elevation of the trail would be one foot above the
one hundred year floodplain. Since it was cleared in NEPA as part of the Preferred Alternative, it
would not require any additional coordination with FHWA.
Option B - Meandering Trail
This option would run parallel to Dubuque Street between Foster and Taft and from south of Taft
would tie in to match the current trail’s meander through Terrell Mill Park. The trail meander
begins south of Taft Speedway and quickly adjusts to match the existing meandering trail
alignment. It would also meet the existing trails elevation, which falls below the desired elevation of
one foot above the one hundred year floodplain. Any time the trail moves beyond 8 feet behind the
back of curb the elevation of the trail is likely to be below the 100+1 floodplain elevation. This
means that there would be times when Dubuque Street may be open while sections of the trail
would be under water. Exact elevations of the meandering trail can be determined during the
design process. The trail will then regain the desired elevation of one foot above the one hundred
year floodplain south of Mayflower where it again runs in parallel to Dubuque Street. Portions of
Iowa City Gateway
Alignment Options for Iowa River Trail Along Dubuque Street
Page 2 of 2
this trail alignment would fall outside the limits associated with the Preferred Alternative for NEPA.
The Preferred Alternative called for the trail to run parallel to Dubuque Street from Foster Road to
Park Road. Because some sections of Option B fall outside the NEPA limits, some additional
coordination with FHWA may be required in order to incorporate this into design.
Iowa City Gateway
Trail Options along Dubuque Street Retaining Wall
Page 1 of 3
Iowa City Gateway
Trail Options along Dubuque Street Retaining Wall
The City Council and staff have requested that HNTB investigate options for the placement of the
Iowa River Trail and other multiuse paths along Dubuque Street and the Iowa River from
approximately Kimball to Park Road. HNTB investigated three options for the trail in this stretch of
the corridor. Those options include the following:
• Option A – Trail on the top of the retaining wall only
• Option B – Trail on top of the retaining wall and multiuse path/River Walk along the base of
the wall with bridge underpass at the east abutment
• Option C – Trail on top of the retaining wall with a new extension south of Park Road in
anticipation of a future path from the Hancher Pedestrian Bridge to Park Road.
The options attempted to strike a balance between providing people the opportunity to connect to
the Iowa River via trails and paths, while also maintaining a minimum of eight feet distance
between the riverbank and the base of the retaining wall. This minimum distance from the
riverbank is required for the construction of a Mechanically Stabilized Earth (MSE) retaining wall.
Any retaining wall built within 8 feet of the riverbank would require a different type of foundation
that is more costly and complicated to construct and would require work in the Iowa River, which
was not cleared during the NEPA process nor approved by the Federal Highway Administration
(FHWA) and other permitting agencies.
Attached for your reference, please find exhibits displaying the trail alignments of each option. Also
attached is a sample of four cross-sections at points along each potential trail alignment. These
display the height of the retaining wall, width of the trail or path and proximity to the river.
Staff considered several factors when assessing the potential benefits and drawbacks of each
option. These included:
• Added cost and constructability
• Width of trails and multiuse paths
• Trail in relation to floodplain elevations
• Minimum distance of wall from the River
• Permitting ease and length of time for approvals
• Visibility of trail and path users from vehicles on Dubuque Street and Park Road.
The table on the following page displays the factors and the performance of each option. An overall
assessment of each option follows below the table. In summary, Option A remains the simplest to
construct, permit and remains at or above the one hundred year floodplain elevation. The other
options entail additional cost to construct and introduce portions of the trail or path that are below
the one hundred year floodplain elevation. The trail south of Park Road included in Option C was
not part of the Preferred Alternative that received FHWA approval. As such, this option could incur
delays in permitting and design due to additional coordination with FHWA and other permitting
agencies.
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Iowa City Gateway
Trail Options along Dubuque Street Retaining Wall
Page 3 of 3
Option A: Trail on Wall Only
This option is the original trail configuration as documented during the NEPA process. This is a 10’
wide trail on the top of the Dubuque Street retaining wall. It is placed eight feet behind the back of
curb and runs the length of the retaining wall. The cost of this option is covered in the base cost for
the project. This option does not include a trail passage under the bridge, but it would keep the
option open for a future extension of the trail to the south to connect with existing trails at the
Hancher pedestrian bridge.
Option B: Trail on and Below Wall
This option has the trail splitting into two paths, beginning near the Dubuque Street intersection
with Kimball Road. The ten-foot wide trail would continue along the top of the wall the same as in
Option A. A six-foot wide path would follow along the base of the wall providing a path along the
river bank. This lower path would continue under the bridge (at an elevation of approximately 645
feet). This is the same elevation as the 10-year flood and it would provide approximately 8.5-feet of
vertical clearance for the trail under the bridge. South of the Park Road Bridge the path is able to
widen to 10-feet and would connect to the upper trail. The lower trail is very close to the edge of
the river and may be difficult to construct, which may result in a higher bid price for this item. The
estimated added cost of this option compared to Option A is approximately $470,000.00.
Additionally, the area south of Park Road was not cleared during the NEPA process as it was not a
part of the Preferred or Reasonable Alternatives considered. Therefore, additional study,
coordination and approval from FHWA and permitting agencies would be required during the
design of the project.
Option C: Trail on Wall and Extended South of Park Road
This option would follow along the top of the retaining wall, the same as Option A until reaching
Park Road. At Park Road, the existing sidewalk would continue to run parallel to Dubuque Street.
Also at Park Road, the second 10-foot wide path would descend along the wall and then pull away
to follow along the bank of the river to connect to the future trail south of the project area. This
option does not provide the chance to have a path under the bridge but it does provide connectivity
to future trails to the south. Because it does not pass under the bridge and because it maintains
greater distance from the riverbank, it improves constructability. Additionally, the area south of
Park Road was not cleared during the NEPA process as it was not a part of the Preferred or
Reasonable Alternatives considered. Therefore, additional study, coordination and approval from
FHWA and other permitting agencies would be required during the design of the project. The
estimated added cost of this option is approximately $240,000.00 above the cost of Option A.
Option A,C
Option B
Section 32+50
8’ 10’ 7’
8’ 10’
2.5’
4.5’
6’
Option A,C
Option B
Section 36+00
8’ 10’ 8.5’
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Option B
Option C
Option A
Section 39+50
8’ 10’ 7.5’
10’
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Option B
Option C
Section 41+00
Option A
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March 19, 2014