HomeMy WebLinkAboutTrans 2011-09-06 Item 2A - Discussion - Tukwila Urban Center Pedestrian-Bicycle Bridge ReportCity of Tukwila
Jim Haggerton, Mayor
INFORMATIONAL MEMORANDUM
TO: Mayor Haggerton
Transportation Committee
FROM: Bob Giberson, Public Works Director
DATE: August 31, 2011
SUBJECT: TUC Pedestrian /Bicycle Bridge
Project No. 90510403
Type, Size and Location Report
ISSUE
Presentation of the Pedestrian /Bicycle Bridge Type, Size, and Location (TS &L) Report and discussion of
options.
BACKGROUND
On August 15, 2011, Staff presented the history of the Pedestrian /Bicycle Bridge project and highlighted
key aspects of the TS &L Report to the Transportation Committee. On August 26, 2011, the Final Draft of
the TS &L Report was distributed to Committee members and the Mayor.
DISCUSSION
Several bridge and trail alignments were studied along with several bridge types. Two ADA compliant
options; ramps and an elevator /stairs combination, were also studied. Cost estimates for these options
are summarized below (details are on pages 78 -79 in the TS &L Report): The estimates are in 2008
dollars and include a 50% design contingency as the level of engineering is not yet complete enough for
a more accurate estimate. The summary and recommendation section from the TS &L Report are
attached.
Total (2008)
Elevator and Stairs
Subtotal
50% Contingency
Total (2008)
RECOMMENDATION
$9,019,344 1 $9,786,821
$9,819,505
$8,691,975
$7,915,395
x
100, 442
11
348, 755
$2,783,500
$3,039,326
$3,050,221
$2,674,378
$2,415,518
$8,350,501
$9,117,978
$9,150,663
$8,023,133
$7,246,553
Discuss the TS &L options and provide direction to Staff on bridge type, size and location to proceed to
final design.
Attachment: Final Draft Section 14: Summary and Recommendation
w: \pw eng \old p drive \cyndy \pedestrian bridge \information memo is &I discussion 9- 6- 11.docx
14. Summary and Recommendations
The proposed pedestrian bridge over the Green River and West Valley Highway is meant to act as a
catalyst between existing and future development. Promoting the use of public transportation and
alternative modes of transport, this vital link will help support densification of the area and a more
walkable lifestyle. It should be easily accessible, ADA compliant, and be aided by understandable and
welcoming wayfinding leading to and from surrounding development. The bridge, its approaches, and
adjacent open space should be safe and inviting at all times of day, providing appropriate lighting at
night and secure storage options for bicycles. In addition, the project should not negatively affect the
existing properties around the site and should in fact benefit and complement those areas so as to
hopefully increase their value.
Of the pathway alignments for the west side of the bridge, Alignment 1 is recommended as the best
option because it evokes the most visually strong link and provides the shortest and most direct route
available.
Bridge Alignment A is recommended for the river crossing because it provides the most direct
connection across the Green River, requires the shortest bridge structure, and can be adapted to
accommodate a future highway crossing. The twin tied arch is recommended for the bridge type
because it provides a functional structure with reasonable cost and fulfills the aesthetic requirements
of the project with its curved members and open design. However, if the City wants to create an iconic
structure and utilize either the inclined arch or single tied arch styles, the premium to the project cost
would be approximately $800,000 or 9 percent more than the twin tied arch project costs.
NEXT STEPS
Following the review and discussion of this report, as the project continues into the final design phase,
it is recommended that the next steps include:
Determine whether the crossing of West Valley Highway should be incorporated into the design
criteria. If so, determine alternatives for crossing the West Valley Highway.
Determine if the City feels that an iconic structure is worth the additional cost to the project.
Refine costs and attempt to define the items included in or reduce the amount of the 50
percent contingency.
Conduct detailed survey of preferred alignment.
City of Tukwila
82 Pedestrian /Bicycle Bridge 2
Study the ability to shorten ramps by providing adhering to the ADA requirement to provide
landings for every 30 inches of rise for a resulting grade of approximately 7 percent versus
5 percent.
Complete detailed geotechnical study to determine final design level information.
Perform final design of plan and profile for selected trail alignment.
Perform final structural design of preferred bridge structure and approaches.
Explore property acquisition alternatives.
Update environmental study and include costs for permitting and mitigations.
Continue coordination with stakeholders.
Asses parking impact with the property owner.
City of Tukwila
Pedestrian /Bicycle Bridge 83
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