HomeMy WebLinkAboutItem 8.1 PrelStudyDwntwnStscape CITY CLERK
File # 600-30
AGENDA STATEMENT
CITY COUNCIL MEETING DATE: November 5, 2002
SUBJECT: Update on Preliminary Studies for the Downtown Streetscape
Improvement Implementation ~
Report Prepared by: danet Harbin, Senior Planner
ATTACHMENTS: 1. Tree Evaluation for Village Parkway (prepared by
HortScience)
2. Preliminary Feasibility Study Report for Pedestrian Bridge
Over Dublin Boulevard at Golden Gate Drive (prepared by
ARUP)
RECOMMENDATION:/ 1. Receive Staff report
2. Hear Consultant's presentation
3. Consider Studies and recommendations
4. Accept Arborist's Tree Evaluation for Village Parkway and
direct Staff to include design and construction of sidewalk
widening project in the Capital Improvement Program
5. Accept Engineer's Feasibility Study for Pedestrian Bridge
and determine to do no further study at this time
FINANCIAL STATEMENT: The funding for the consultants' work for preparation of the studies
is included in existing funds in Capital Improvement Program
Project #94060 for FY 2002-2003. These studies have been
prepared as part of the work program for the Downtown Streetscape
Implementation Program.
BACKGROUND:
In November 1999, the City Council directed staff to prepare three Specific Plans for various portions of
the downtown area of Dublin to guide the development and revitalization of the West Dublin BART,
Downtown Core and Village Parkway areas. The Specific Plans were adopted by the City Council on
December 19, 2000. As a part of the implementation of the three downtown Specific Plans adopted by the
City Council on December 19, 2000, streetscape improvements are necessary in the West Dublin BART,
Downtown Core and Village Parkway Specific Plan areas to provide continuity and unifying elements to
establish a positive image in the downtown area.
DESCRIPTION:
Prior to construction of the downtown streetscape improvements, the basic designs for the streetscape
elements and other physical improvements for the three areas were to be determined. Additionally, two
preliminary studies were fimded in the Capital Improvement Program budget for CIP project #94060 for
COPIES TO: Project File
ITEM NO.
GSDowntown Streetscape Impr\CC-srStudyUpdate.doc
Fiscal Year 2002 to 2003, related to background infOrmation on specific aspects of the improvements
proposed for the streetscape and pedestrian accessibility on Dublin Boulevard and Village Parkway. One
of the preliminary studies needed to determine the extent of the sidewalk improvements on Village
Parkway was an arborist's report on the condition and the potential success of preserving or relocating the
existing trees in the sidewalks. The other preliminary study needed for determining the extent of
streetscape improvements on Dublin Boulevard was an engineering study of the feasibility of constructing
a pedestrian bridge across the roadway at the intersection of Golden Gate Drive.
ANALYSIS:
The City's consultant for this project, Dave Evans of Singer Fukushima Evans, Inc. subcontracted with
the horticultural firm HortScience to prepare the arborist study (Attachment 1), and with the engineering
firm ARUP to prepare the bridge feasibility study (Attachment 2). Mr. Evans will make a presentation on
the studies and related findings at the City Council meeting on the project. Below is a brief summary of
the consultants' findings.
Arborist Study Findings: A~ Tree Evaluation study for Village Parkway was prepared on May 11, 2002
by HortScience to evaluate the existing trees on Village Parkway and their potential to be incorporated in
the sidewalk widening project and streetscape through preservation, or if preservation was not possible,
'relocation elsewhere within the new pavement area. The Public Works Department and Maintenance
Division have reviewed the study, as has the Community Development Department. The sidewalks are
proposed for widening to 8 or 10 feet under a separate Capital Improvement Program project. The
existing street trees (Bradford Pears) along Village Parkway are located in tree wells within the existing 4
½-foot wide sidewalk. Staff had concerns that the demolition of existing sidewalk pavement, removal of
surface roots, and the installation of new pavement to a depth of 8 inches (typical) might damage the
trees.
The arborist's study found that of the 40 Bradford Pear trees located along Village Parkway, 39 are in
moderate to good condition. The study also determined that although the installation of new pavement
will require significant root pruning, the trees should tolerate the treatment and survive. This
determination is based on the trees being presently in good health. Half of the trees have already
successfully withstood root pruning for replacement of pavement that the roots had previously displaced.
The arborist also suggested additional pruning to minimize the potential for branch failure for long-term
management and maintenance of the street trees.
Pedestrian Bridge Feasibility Study Findings: A Preliminary Feasibility Study Report for the location
of a potential pedestrian bridge over Dublin Boulevard at Golden Gate Drive was submitted on September
10, 2002 by the engineering consultant, ARUP, and reviewed both by the Public Works Department and
the Community Development Department. The purpose of the bridge would be to provide a safe
pedestrian link between the existing shopping area north of Dublin Boulevard to the future West Dublin
BART station and potential development to the south of the roadway.
The engineering report determined that the bridge would be 10 feet wide and span approximately 150 feet
across Dublin Boulevard. Depending on the type of ramp design selected for the bridge, the access ramps
with a single switchback would be 117 feet in length on either side of the roadway, or 80 feet in length on
either side with double switchback ramps. Both designs would be in conformance with the Americans
with Disabilities Act requirements for handicap accessibility. With a design option utilizing an elevator
and stairs only, without ramps, 28 feet would still be required on either side of the roadway for a footpath,
fencing and structure. The north access ramp to the bridge would impact the parking lot of the Toys R Us
store, and the landscaped berm adjacent to the Washington Mutual Bank building would be impacted by
the access ramp to the south. Stairs could be provided for non-ramp access from the sidewalks to the
upper span of the bridge within the structure with all of the design options. ~ .
The estimated design, management and construction costs for the pedestrian bridge are $3.7 million for a
basic design, and $4.5 million for an aesthetically driven design; however, this cost estimate does not
include the cost of removal of the row of parking at the Toys R Us site or the cost to relocate the parking
elsewhere in the shopping Center. Those would be additional costs that would need to be determined if
the City decided to go forward with construction of the pedestrian bridge across Dublin Boulevard. Other
costs that might be incurred, but are difficult to determine, relate to the potential loss of business for
business owners at the Dublin Place shopping center and for those businesses across Dublin Boulevard to
the south during construction, and the impacts of construction on Dublin Boulevard, a main thoroughfare
in the City. In addition to these costs, there would be future costs related to the maintenance of the
structure and also operational costs if elevators are included in the design.
CONCLUSION: Based on the arborist's analysis of the condition of the trees located along Village
Parkway, and his determination that the trees could successfully withstand root pruning to install
additional sidewalk paving, future improvements and widening of the sidewalks may proceed as planned.
Staff recommends that the City Council accept the arborist's report and that direction be given to Staff to
include the design and construction of the sidewalk widening project for Village Parkway in the Capital
Improvement Program
Staff recommends that the Pedestrian Bridge Feasibility study be accepted, but no further study of the
project be conducted at this time as the project would be an expensive endeavor for the City to undertake
and may adversely affect businesses in the downtown area. The project would require acquisition of
property from the owner of the Dublin Place shopping center and the Washington Mutual Bank, and the
need to replace the parking area that will be used for the bridge ramps. Other costs that would be
incurred, but have not been estimated in this preliminary study, relate to maintenance of the structure and
operational costs if elevators are included in the design. Additionally, from field observations, the
volume of pedestrian traffic crossing Dublin Boulevard at the present time does not justify the anticipated
cost of the bridge. If the volume of pedestrian traffic in this area does increase substantially in the future,
the City Council may want to reconsider the issue.
RECOMMENDATION: Staff recommends that the City Council: 1) Receive the Staff report; 2) Hear
the Consultant's presentation; 3) Consider the studies and recommendations; 4) Accept the Arborist's
Tree Evaluation for Village Parkway and direct Staff to include design and construction of sidewalk
widening project in the Capital Improvement Program; and, 5) Accept the Engineer's Feasibility Study
for Pedestrian Bridge and determine to do no further study at this time.
,, Horliculturai Consultants
·
·
_. October 22, 2002
·
Mr. David Evans
Singer Fukashima Evans
5 Crow Canyon Court, Suite 200
San Ramon CA 94583
Subject: Tree evaluation
Village Parkway, Dublin
Dear David
·
SFE is designing potential new streetscapes for the section of Village Parkway between
Dublin Blvd. and Amador Valley Blvd. You requested that HortScience, Inc. evaluate the
existing trees and their potential to be incorporated into a new design. As you are aware,
I examined 47 trees. This letter summarizes my observations and assessment.
Survey Methods
The survey was carried out during February 2002. The included all trees within the Street
right-of-way on the east and west sides of Village Parkway. The' survey procedure
consisted of the following steps:
1. Identifying the tree as to species.
2. Tagging each tree with an identifying number.
3. Measuring the trunk diameter at a point 54" above grade.
4. Evaluating the health and structural stability using a scale of 1-5:
5-A healthy, vigorous tree, reasonably free of signs and symptoms of disease,
with good structure and form typical of the species.
4 - Tree with slight decline in vigor, small amount of twig dieback, 'minor
structural defects that could be corrected.
3 - Tree with moderate vigor, moderate twig and small branch dieback, thinning
of crown, poor leaf color, moderate structural defects that might be mitigated
with regular care.
2- Tree in decline, epicormic growth, extensive dieback of medium to large
branches, significant structural defects that cannot be abated.
1 - Tree in severe decline, dieback of scaffold branches and/or trunk; most of
foliage from epicormic shoots; extensive structural defects that cannot be
abated.
5. Noting the presence of any defects in structure, pests or other problems.
6. Estimating the height of the tree and clearance from the ground.
7. Measuring the size of the planting space (also called the pavement cutout).
8. Evaluating the amount of damage to pavement such as displacement of curb and
sidewalk panels, presence of patching, grinding of lifted pavement and cracks.
9. Rating the suitability for preservation for each tree.
· R0. Box 754
Pieasant0n, CA 94566
f' '"'" ~'~ ~' '' '~' ']~'~HI "~ Phone: 925 484 0211
:= t acnlq n 6096
wwv. hort$¢i~no~.~om
Letter to David Evans HortScience, Inc.
Tree evaluation, Village Parkway, Dublin CA Page 2
Description of Trees
Forty-seven (47) trees were evaluated. Tree tag numbers begin (#505) on the west side
of Village Parkway at the intersection with Dublin Blvd. (at the McDonalds), proceed north
to tree #530, cross to the east side, proceed south back to Dublin Blvd. (trees #531 -
551).
Table 1. Condition ratings and frequency of occurrence of trees within the street
right-of-way. Village Parkway. Dublin CA.
Common Name Scientific Name Condition Rating No. of
Poor Moderate Good Trees
(1-2) (3) (4-5)
Carob Ceratonia siliqua 1 .... 1
Olive Olea europaea .... I 1
London plane Platanus x acerifolia .... 3 3
Purpleleaf plum Prunus cerasifera 'Atropurpurea' -- 1 - 1
Bradford pear Pyrus calleryana 'Bradford' I 6 33 40
Valley oak Quercus Iobata .... 1 1
Total 2 7 38 47
Bradford are found exclusively along the east and west sides of Village Parkway. They
dominate this section of the streetscape. The carob, olive, London planes and purpleleaf
plum are part of landscape of businesses adjacent to the street, generally set back from
the sidewalk.
The Bradford pears are typical of this cultivar. Over 80% are in good condition with
dense crowns and vigorous growth. Trunk diameters range from 6" to 18"; the majority
are between 12" and 15". Tree crowns are typical of Bradford pear: codominant and
multiple stems arising from one point are common. Attachments among these stems are
often poor, also typical of the cultivar. In addition, many scaffold branches have become
heavy. As trees increase in size, these limbs will add more weight with increasing
potential to fail. There have been several branch failures already (e.g., #538, 545).
There has been some level of sidewalk repair adjacent to 20 of the 40 pears. Treatment
has ranged from grinding to replacement. There does not appear to be any relationship
between sidewalk treatment and tree condition, i.e., trees that have had sidewalks
removed and replaced are in as good condition as those where the original pavement is
present.
The olive, valley oak and London plane are in good health. Fruit production by the olive
has been heavy. The purpleleaf plum is in fair condition and has poor crown structure.
The carob is poor.
Descriptions of individual trees are found on the enclosed Tree Survey Form.
Letter to David Evans HortScience, Inc.
Tree evaluation, Village Parkway, Dublin CA Page 3
Potential to Incorporate Pears into a new Streetscape
We discussed your ideas for a new streetscape. You would like to enlarge the existing 6'
sidewalk to 10' by extending the pavement. This would involve demolishing the existing
pavement, removing any surface roots to the depth of a new section (12") then installing
new pavement. You asked me to comment on the potential to incorporate the trees into
this design. There are two considerations:
· Response of Bradford pears to construction
The proposed design would require significant root pruning. All roots within the.
top 12" of soil would be removed, probably on three sides as the sidewalk is
enlarged around the trees. Assuming that roots within the pavement section can
be pruned clearly and that demolition will not incur damage beyond this removal,
the trees should tolerate the treatment.
I base this assessment on two factors. First, the trees are in good health, an
important consideration to root removal. Second, half of the pears have
displaced the adjacent pavement. Where pavement has been replaced, tree
roots have been removed without adversely affecting the health and stability of
the pears.
· Long-term management
As Bradford pears mature, their poor crown structure becomes increasingly
problematic. Scaffold limbs become long and heavy. They fail during storm
events.
Trees along Village Parkway are mature. Branch failures have occurred in six
trees. Heavy lateral branches are developing in others. This will occur whether
or not a new street design is implemented.
There is a trade-off in retaining the trees. Incorporating them into a new street
order will require additional pruning to minimize the potential for branch failure.
The pears will be shorter-lived than a new planting. On the other hand, the pears
offer the benefit of their size.
/
The Bradford pears found along this section of Village Parkway represent the typical
mature tree of this species. They are in excellent health, provide two seasons of interest
(spring flowers and fall color) as well as shade the sidewalk and have no pest problems.
At the same time, the trees possess the branching structure found in this cultivar: poorly
spaced scaffold that may develop end weight and are prone to failure during storms.
I anticipate that the trees will continue to provide these benefits for at least 10 years, if
not 15 or 20, after the project is complete. I base this assessment on the several factors.
First, the trees are growing vigorous with an upright form. As Bradfords age, they can be
expected to become rounder in form. Second, Bradford pears normally mature at 40 -
50' tall. The surveyed trees are but 30' tall.
Retaining these trees with their present vigor will require additional pruning to foster good
crown structure. Pruning should concentrate on two goals: 1) sub-ordinating long
laterals as they develop end weight and 2) removing crowded lateral branches as they
are suppressed. Under no circumstances should the trees be topped or over-thinned.
Letter to David Evans HortScience, Inc,
Tree evaluation, Village Parkway, Dublin CA Page 4
Preservation Guidelines
The following guidelines should be incorporated into the design specifications to
minimized impacts from construction around the trees.
Design recommendations
1. Trees to be preserved should be included on all plans.
2. The Consulting Arborist shall review all project plans with regard to tree
impact and necessary protection measures.
3. A TREE PROTECTION ZONE shall be established around each tree to be
preserved: 1' back from the edge of the proposed sidewalk. No grading,
excavation, construction or storage of materials shall occur within that zone.
4. Any new underground services including utilities, sub-drains, water or sewer
shall be routed in the street or outside the dripline
5. Tree Preservation Notes, prepared by the Consulting Arborist, should be
included on all plans.
6.Any herbicides placed under paving materials must be safe for use around
trees and labeled for that use.
7.Irrigation systems must be designed so that no trenching will occur within 10'
of the trunk of any tree.
Pre-construction and demolition treatments and recommendations
1. The demolition contractor shall meet with the Consulting Arborist before
beginning work to discuss work procedures and tree protection.
2. Fence all trees to be retained to prior to the onset of any construction or
demolition. Fences shall be 6 ft. chain link or equivalent as approved by
consulting arborist. Fences are to remain until all grading and construction is
completed.
3. Apply and maintain 4-6" wood-chip mulch within the TREE PROTECTION ZONE.
Tree protection during construction
1. Prior to beginning work, the contractors working in the vicinity of trees to be
preserved are required to meet with the Consulting Arborist at the site to
review all work procedures, access routes, storage areas and tree protection
measures.
2. Any grading, construction, demolition or other work that is expected to
encounter tree roots should be monitored by the Consulting Arborist.
3. Demolition of the pavement shall Use the smallest equipment possible and
excavate the minimal amount of soil
4. Following demolition, the location of the new sidewalk should be staked or
identified. Roots shall be pruned 6" back from edge of the new walk.
Letter to David Evans HortScience, Inc.
Tree evaluation, Village Parkway, Dublin CA Page 5
5. If injury should occur to any tree during construction, it should be evaluated
as soon as possible by the Consulting Arborist so that appropriate treatments
can be applied.
£
6. No materials, equipment, spoil, waste or wash-out water may be deposited,
stored, or parked within the TREE PROTECTION ZONE (fenced area).
7. Any herbicides placed under paving materials must be safe for use around
trees and labeled for that use. Any pesticides used on-site must be tree-safe
and not easily transported by water.
8. Ali trees shall be irrigated on a schedule to be determined by the Consulting
Arborist. Each irrigation shall wet the soil within the TREE PROTECTION ZONE
to a depth of 30".
9. Any roots damaged during grading or construction shall be exposed to sound
tissue and cut cleanly with a saw.
Poet-construction maintenance
Following construction, a maintenance plan including pruning, irrigation and fertilization
must be developed. Future pruning should focus on the subordination of heavy scaffold
branches and the removal of poorly structured limbs.
If you have any questions regarding my observations, please feel free to contact me. I
look forward to hearing from you.
James R. Clark, Ph.D.
Certified Arborist WC-0846
Enc. Tree Survey Form
·
· ·
·
~:~ February 2002
TREE SPECIES TRUNK CONDITION SUITABILITY SIDEWALK COMMENTS
No. DIAMETER 1=poor for REPAIR?
(in.) 5=excellent PRESERVATION
505 Carob 12 2 Poor Large trunk wounds; very poor form; crown raised.
506 Bradford pear 14 4 Moderate Ground Multiple attachments @ 8'.
507 Bradford pear 15 4 Moderate Multiple attachments @7'; developing heavy lateral
branches to NW & N.; N. limb is hazard beam.
508 Bradford pear 12 4 Moderate MultiPle attachments @ 10'; developing heavy lateral
branches to E.
509 Bradford pear 15 3 Poor Codominant trunks @ 6' with poor attachment, trunks
wrapped around one another.
510 Bradford pear 12 4 Moderate Multiple attachments @ 8' with included bark.
511 Bradford pear 14 4 Moderate Ground Multiple attachments @ 8'; developing heavy lateral
branches to E. & SE.
512 Bradford pear 14 3 Poor Multiple attachments @ 8'; poor attachment; spreading
apart.
513 Bradford pear 14 4 Moderate Multiple attachments @ 8' with codominant attachments
higher in crown; upright scaffolds.
514 Bradford pear 14 4 Moderate Multiple attachments. @ 8'; upright.
515 Bradford pear 15 4 Moderate Multiple attachments @ 8'; developing heavy lateral
branches to N:; crowded.
516 Bradford pear 11 4 Moderate Multiple attachments @ 6'; developing heavy lateral
branches to N.
517 Bradford pear 12 3 Poor Codominant trunks @ 8' with very poor attachment.
518 Bradford pear 10 4 Moderate Developing heavy lateral branches to N.; good form
otherwise.
519 Bradford pear 11 4 Moderate Multiple attachments @ 8'; developing heavy lateral
branches to N. & E. ~,,
Page 1 ~
· ·
·
TREE SPECIES TRUNK CONDITION SUITABILITY SIDEWALK COMMENTS
No. DIAMETER 1=poor for REPAIR?
(in.) 5=excellent PRESERVATION
520 Bradford pear 6 4 Moderate Codominant trunks @ 5' with very poor attachment;
crowded.
521 Bradford pear 15 4 Moderate Multiple attachments '@ 12' with upright scaffolds;
develOping heavy lateral branches to N.'
522 Bradford pear 14 4 Moderate Panel replaced Multiple attachments @ 8'; developing heavy lateral
branches to S.
523 Bradford pear 10 4 Moderate Panel replaced Multiple attachments @ 9' with poor attachment; upright.
524 Bradford pear 15 4 Moderate Multiple attachments @ 8'; developing heavy lateral
branches to NE; trunk wound on N.
525 Bradford pear 13 4 Moderate Ground Good branch spacing but scaffolds becoming heavy,
particularly to E.
526 Bradford pear 10 4 Moderate Codominant trunks @ 4' with very poor attachment.
527 Bradford pear 14 4 Moderate Panel replaced Multiple attachments @ 8'; developing heavy lateral
branches to NE.
528 Bradford pear 12 4 Moderate Lifted, patched Multiple attachments @ 8'; poor attachment; branch
failure on N.; developing heavy lateral branches to S.
529 Bradford pear 12 4 Moderate Multiple attachments @ 8' & codominant trunks @ 10';
crowded.
530 Bradford pear 13 4 Moderate Multiple attachments @ 8'; crowded.
531 Olive 10,10,9,6,4, 5 Good Multiple attachments @ base; lots of fruit; good form.
4
532 Bradford pear 13 4 Moderate Multiple attachments @ 8'; upright except for developing
heavy lateral branches to S.
Page 2 ~:~
· ·
· · ·
~'~*~ '" ~; , Village Parkway
TREE SURVEY Dublin CA
~ :,~,,~ ;i_.,? February 2002
im
TREE SPECIES TRUNK CONDITION SUITABILITY SIDEWALK COMMENTS
No. DIAMETER 1=poor for REPAIR?
(in.) 5=excellent PRESERVATION
533 Bradford pear 18 4 Moderate Multiple attachments @ 8'; branch failure; developing
heavy lateral branches to W. but otherwise upright.
534 London plane 21 4 Good Irregular form: codominant trunks @ 10', good
attachment.
535 Bradford pear 13 4 Moderate Panel replaced Codominant trunks @ 8'; upright.
536 Bradford pear 16 4 Moderate Multiple attachments @ 12';upright but developing heavy.
lateral branches to N.
537 ValleY oak 6 4 Moderate Multiple attachments @ 12'; needs to be corrected.
538 Bradford pear 16 4 Moderate Panel replaced Codominant trunks @ 8' upright but Iow scaffolds to N. &
E. developing heavy lateral branches; branch failure.
539 Bradford pear 9 3 Moderate Ground Crown raised leaving heavy laterals; sparse canopy.
540 Bradford pear 12 3 Moderate Ground Multiple attachments @ 7' & codominant trunks @ 12';
developing heavy lateral branches to N.; branch failure.
541 Bradford pear 17 4 Moderate Ground Multiple attachments @ 8', most starting to develop
weight & spread apart.
542 Bradford pear 18 4 Moderate Panel replaced Multiple attachments @ 8', crowded!; most scaffolds
starting to develop weight & spread apart.
543 Bradford pear 18 4 Moderate Panel replaced Multiple attachments from 8-10'; poor attachments;
generally upright.
544 Bradford pear 18 4 Moderate Panel replaced Multiple attachments @ 8','most starting to develop
weight & spread apart; branch failure.
545 Bradford pear 15 4 Moderate Ground Multiple attachments @ 8', developing weight &
spreading apart; branch failure.
Page 3 ~
· ·
TREE SURVEY '
Dublin GA
February 2002
· '
TREE SPECIES TRUNK CONDITION SUITABILITY SIDEWALK COMMENTS
No. DIAMETER 1=poor for REPAIR?
(in.) 5=excellent PRESERVATION
546 Bradford pear 9 2 Poor Ground Large wound @ base on E.; leans E.; codominant trunks
@ 6 & 7'; developing heavy lateral branches to N.
547 Bradford pear 14 4 Moderate Panel replaced Multiple attachments @ 8'; crown thinned; developing
heavy lateral branches to E.
548 London plane 14 4 Good Irregular form.
549 Bradford pear 10 3 Moderate Panel replaced Sidewalk widened; bowed SW away from #548; poor
form.
550 Purpleleaf plum '5,4 3 Moderate Series of codominant attachments; small tree.
551 London plane 14 5 Good Good tree.
Page 4 ~-~
City of Dublin
Singer, Fukushima,
~-- Evans. Inc.
Pedestrian Bridge Over
Dublin Boulevard at
Golden Gate Drive
~" Preliminary Feasibility
,... Study Report
~-- ~. October 24, 2002
TT Cfl EHT
City of Dublin
Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
Preliminary Feasibility Study Report
October 2002
Ove Arup & Partners California Ltd
901 .Market Street, Suite 260, San Francisco CA 94103
Tel 415 957 9445 Fax 415 957 9096
www. aru p.com
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
CONTENTS
Page
1 EXECUTIVE SUMMARY
2 INTRODUCTION 2
~-~ 3 EXISTING INFORMATION 2
~ 4 COMMON ENGINEERING ISSUES 3
4.1 Vertical Clearance 3
~ 4.2 Main Span Structure 4
4.3 Screening 4
~ 4.4 Americans with Disabilities Act (ADA) 4
~ 5 BRIDGE PLACEMENT 5
6 RAMPS/STAIRS 5
6.1 Pedestrian Travel Time 7
6.2 Ramp Structural Systems 8
7 UTILITIES 8
8 COSTS 8
9 NEXT DESIGN AND ENGINEERING STEPS 9
10 CONCLUSIONS 10
Al. Pedestrian bridge examples 1
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
1 EXECUTIVE SUMMARY
At the request of the City of Dublin, Singer, Fukushima, Evans (SFE) was tasked with
r-- performing a preliminary feasibility study for a pedestrian bridge over Dublin Boulevard at
Golden Gate Drive. FSE invited Arup to assist in the study and prepare this engineering
("'~ report.
e-'- The intended purpose of the pedestrian bridge is to provide a pedestrian link between the
existing shopping areas to the north of Dublin Boulevard with a proposed mixed-use
r--, development at the future West Dublin/Pleasanton BART Station to the south.
Questions to be answered by this study, in very general terms, are:
· Is it physically possible?
· What is possible? - location, size, ramp configurations
· What is the approximate cost?
~' The informational basis of this report is:
e-- · Discussions with SFE
,-~ · Various hardcopy drawings of limited dimensional content showing some curb and
gutter locations and roadway widths.
· One field visit to walk and photograph the site.
Electronic files of street layouts, property/right-of-way lines, utilities, and driveway and
building locations were not available during the study.
This study locates a bridge 10 feet wide and 150 feet long crossing Dublin Boulevard on the
r-' west side of Golden Gate Drive. This site selection was predominantly due to the available
footprint for access ramps 240 feet in length as required by the Americans with Disabilities
Act. The existing land use for the ramp landing area in the northwest quadrant of the
Dublin Boulevard/Golden Gate Drive intersection is parking for Toys r Us and in the south
~" west quadrant, landscaping for the Washington Mutual Bank building.
~ Future considerations for this bridge layout may include eliminating the at-grade pedestrian
crossing at this location on Dublin Boulevard as a means of improving vehicular traffic
,-- flow. S~irs have been shown to permit direct, non-ramp access between the main bridge
and the sidewalks to expedite pedestrian flow.
Estimates of costs have been generated based on square-feet pricing of similar facilities.
~., The estimated construction cost for the bridge and the ramps ranges from about $3 million
for a simple crossing to $4 million for an aesthetically driven design. These costs include
r", estimates of land acquisition, project administration and utility relocations.
Should the City of Dublin choose to advance this pedestrian bridge study, next steps for the
r-, bridge design would include: an exhaustive search of as-built drawings for all street, utility
and private property improvements within and adjacent to the site; site survey for vertical
'-' and horizontal geometric information; and meetings with City Officials and the public to
r.~ establish aesthetic and functional design guidelines.
~" 1 Amp for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
2 INTRODUCTION
r-., As the prospect approaches of turning a large parcel of land north of 1-580 and adjacent to
the future West Dublin/Pleasanton BART Station into an active mixed-use development, the
r'- City of Dublin is interested in creating pedestrian friendly connectivity with the existing
commercial areas in their City.
Figure 1 - ProjeCt LocatiOn
The City of Dublin requested that Singer, Fukushima, Evans (SFE)undertake a preliminary
feasibility study of a pedestrian crossing. SFE invited Ove Arup & Parmers California
Limited (Amp) to undertake the preliminary feasibility engineering and cost estimating for
the project. This report summarizes the efforts of Arup.
3 EXISTING INFORMATION
In an effort to contain costs at this early stage in the project, readily available existing
information served as the basis upon which the study was undertaken. The existing
information includes the following hardcopy drawings
· "Dublin Boulevard Widening", sheet 7 of 26 (1991)
· "Improvement Plans - Golden Gate Drive", sheet 7 (Rev. 2 - 1971)
· "Dublin Access, Grading, Drainage & Utility Plan of Expo Design Center", sheet
C13 of 14 (1998)
* "Plan & Profile Portion of Dublin Blvd. Proposed Golden Gateway", drawing 3 of 3
(Rev 4 -1968)
· Caltrans' 1-580/680 Direct Connector Project "LAYOUT", drawing L-5 for St.
Patrick's Way - Contract Number EA-233921, Sheet 24 of 1111
Other than the 1971 improvement plans for Golden Gate Drive, the above drawings were
only used for 'scaling' of dimensional information due to their lack Of specific geometric
details. The 1971 plans only included geometries for defining Golden Gate Drive without
curb cuts for driveway accesses. These drawings were created prior to the construction of
St. Patrick's Way. Please note that scaling is not an accepted means of basing detailed
2 Amp for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
.?~/,~;~ ~ '~.~7'~
engineering studies and designs. The use of 'scaling' was dictated by the available
resources and was deemed sufficient for this early study.
Further information/knowledge of the site and the project was gathered from discussions
with SFE and with a site visit to walk the area.
4 COMMON ENGINEERING ISSUES
Rules, both legal and practical, govern the placement and geometric configuration of
pedestrian bridges in the US. These will be discussed in general terms first followed by
issues specific to Dublin Blvd./Golden Gate Drive location.
4.1 Vertical Clearance
The minimum vertical clearance over Dublin Boulevard is taken as 16'-0". This clearance
is typical of main routes throughout the State. Figure 2 is a schematic representation of how
minimum vertical clearance is defined.
Bridge 12 max
. 150 feet
i-
Figure 2 - Elevation Showing Vertical Clearance
Note that the 16'-0" is to the underside of the finished bridge. With an allowance for
approximately 2'-0" of structure, the surface of the pathway will be 18'-0". This is truly a
minimal clearance. Typically an additional few feet of vertical clearance would be added to
allow for construction scaffolding.
The profile shown accepts that the bridge superstructure can be erected during a short period
when Dublin Boulevard is closed to traffic or that a temporary reduction in headroom is
possible should construction scaffolding be required. The intent is to minimize the height of
the deck to reduce the visual impact and minimize the height the crossing users must climb.
Dublin Boulevard traffic closure for a pre-assembled bridge might be 12 hours as compared
to reduced headroom durations for a bridge built on-site which would be in the 4 to 8 month
range.
3 Arup for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
4.2 Main Span Structure
The more structure that is below the feet of the pedestrians, the higher they must climb to
cross the road and the longer the ramps are to get them to that height. This simple rule
dictates much in the way of structural type for the main span.
Remembering the need for vertical clearance over the roadway, any structure placed
between this clearance envelope and the surface of the path requires more climbing and
more ramps. The vast majority of highway bridges place the structure in this location, under
the road. For highways, structure below road is an economical capital investment. The
long-term penalty is that every vehicle must climb higher as a result.
Pedestrians and cyclists receive more consideration than vehicular travel. For this reason,
the supporting structure of many pedestrian crossings is from above the deck rather than
below. Favored structural systems and recognizable examples include:
· Thru-trusses (a small version of the lower deck of the Bay Bridge's East spans)
· Cable-stayed (a small version of the Sunshine Skyway in Tampa, Florida)
· Suspension (a small Golden Gate without the deep stiffening truss below the
roadway)
· Arch (the recently completed pedestrian/bicycle bridge in Berkeley over 1-80)
All of these structural types can be designed to support a shallow deck from above to keep
the pathway profile as close to the vertical clearance envelope as possible.
4.3 Screening
The State of California Department of Transportation requires a screen 8 feet 4 inches high
on all pedestrian crossings to protect the roadway below. With holes no larger than one inch
by inch, the screens prevent large pieces of debris from falling onto the roadway and traffic.
Incorporating high, visually dense, screens into a bridge design such that it is not the main
visual design feature is always a challenge on pedestrian bridges.
4.4 Americans with Disabilities Act (ADA)
The Federal Government requires that public and private facilities open to the public are
accessible by all members of the population. ADA access can be in the form of ramps
and/or lifts and elevators.
Within reason and particularly where the facility is new, the ADA has been interpreted to
also require that the access location is similar for disabled and non-disabled members of the
population. The assertion is that disabled users should not have to travel greater distances to
access the same spaces as non-disabled users.
For the Dublin Boulevard Crossings, the issue of similar access locations would suggest that
a stair from the sidewalk up to the bridge would have to be accompanied by a ramp or
elevator accessible from roughly the same sidewalk location.
The Americans with Disabilities Act limits the incline of public ramps to either:
· 1 foot of vertical rise for every 20 feet of horizontal run with no landings required.
or
4 Amp for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
· 1 foot of vertical rise for every 12 feet of horizontal run with level landings required
r-- every 30 feet.
Figure 3 provides a graphic depiction of these requirements.
r~ PATHWAY ~---/.~, ~VEL
~-- PATHWAY I SURFACE
LEVEL
UNLIMITED · I 30' MAXIMUM
5'-0"
ELEVATION ELEVATION
Continuous Grade Maximum Grade
,-- Figure 3 - ADA Vertical Geometry Limits for Ramps
~' 5 BRIDGE PLACEMENT
~., Ideally, a pedestrian flow study would be undertaken to provide origin-destination
information for the public's movements through the area upon completion of the new.
r" development. For this study, land-use and geometries were the crkeria for placing the
crossing.
~ For discussion purposes, the properties on the four corners of the Dublin Boulevard/Golden
Gate intersection will be referred to as:
· Bank -Washington Mutual on the southwest quadrant
· Parking Lot - Toys-R-Us parking lot on the northwest quadrant
· Car Dealer - Crown Chevrolet on the southeast quadrant
~ · Garage - Auto Repair garage, now empty, on the northeast quadrant
r- Locating the pedestrian crossing facility on the west side of Golden Gate Drive was driven
by the available space in the ample parking lot on the north and landscaped area between the
~" bank building and Golden Gate drive on the south of Dublin Boulevard.
r--, An alignment to the east of Golden Gate Drive has impacts on Car Dealer and the Garage.
There is no 'available' land between program space on the properties and the sidewalks on
~ both sides of Dublin Boulevard. The east alignment would require significantly reduce
street frontage of the Car Dealer and would take the aisle of parking to the west of the
,-, Garage.
RAMPS/STAIRS
Access to the bridge over Dublin Boulevard can be provided by ramps suitable for
combined bicycle and pedestrian usage. The options in Figures 4 through 6 show ramp
5 Amp for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
r'-~ configurations with increasing numbers of switchbacks resulting in shortening of the overall
, r--, length of the facility.
Note: the plan and elevation are ndicative of pathway geometry only and are not intended to reflect structural
aesthetics or architectural treatments
Figure 4 - Single Switchback - Straight Stair
Note: the plan and elevation are indicative of pathway geometry only and are not intended to reflect structural aesthetics or
architectural treatments
Figure 5 - Double Switchback - Straight Stair
6 Amp for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
~£1~votor
£1evoUo~
Note: the plan and elevation are indicative of pathway geometry only and are not intended to reflect structural aesthetics or
architectural treatments
r- Figure 6- Elevator/Stair
,-. The rule of thumb for the number of switchbacks is - the length in the North-South direction
reduces as the as the number of switchbacks increases.
Path width is commonly selected based on the number of users and their activity -
pedestrian or bicycle. For this study, the pathway width was selected as 8 feet to
r' accommodate a large majority of pedestrians. The 8 feet represents a clear width for users.
,,. The 10 feet shown in Figures 4 through 6 is the overall footprint of the bridge including the
need for barrier rails and fencing on each side of the 8 foot pathway.
r' Should the City elect to tie the bridge into a bicycle path network or should this become a
,,-- prominent route for school children, then a wider deck of 10 feet should be considered.
~ 6.1 Pedestrian Travel Time
,.... In general, the slope of ADA compliant ramps does not slow the walking speed of the
pedestrian, especially if the up and down travel is balanced as is the case with the Dublin
r-, Boulevard Crossing. Including switchbacks, however, does increase the travel distance of
the pedestrian. Using a simple rule of thumb that the average person walks at a pace of 4 ft
,~ pet- second, the added travel time based purely on horizontal distance, is readily calculated.
One switchback per ramp is 234 feet in total (2x117 feet) of added travel at 4ft/sec results in
"" 58 seconds per ramp and a total of 1 minute and 56 seconds for the total trip over the bridge.
Stairs would be less impacting on travel time. Stairs tend to reduce the horizontal pace by
half such that the added travel time for two 26 fi. stairs is roughly 26 seconds.
Comparison of the total change in pedestrian travel time from the existing condition at
Dublin \Boulevard to the proposed condition with the bridge in place and closing the at-
t'- 7 Amp for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
grade crosswalk requires additional information. Specifically, the phasing of the traffic and
pedestrian signals would have to be established.
6.2 Ramp Structural Systems
Ramps for pedestrian and bicycle crossings are often the most cumbersome portions of the
facility to design. In the case of the proposed Dublin Boulevard crossing, the flat
topography requires the accommodation of the full 17'-6" vertical change and the
accompanying 240+/- feet of horizontal mn as per the ADA requirements.
Two schools of thought are applied to ramp structures, embankments and elevated.
Embankments are either earthen berms or retained earth structures that support a paved
path. Elevated ramp structures are bridges with columns and decks supporting the path until
the path is near enough to the ground to transition to an embankment.
Several issues contribute to the decision to use an elevated or embanked structure:
Cost: for paths up to 8 to 10 feet above the surrounding grades, embankments and retained
structures are generally less expensive. The differential can be a factor of at least 2.
Safety: Embankments eliminate unsafe areas below the path for possible loitering.
Depending on the paths surroundings, an embankment can also create an unsafe area
concealed by creating a visual barrier. Elevated structures can be designed with fencing to
prevent loitering that is sufficiently transparent to prevent the creation of concealed areas.
Aesthetics: Elevated structures are generally visually lighter and porous which reduces the
public's perception that the ramps are a barrier. If the paths environs do not contain view
sheds or critical visual elements, embankments can be designed and landscaped to become
an asset to an area.
Utilities/Easements: Where paths cross or follow the alignment of utilities and easements,
accessibility to underground facilities is often a requirement. Elevated structures can be
built with columns and foundations designed to permit access while embankments of any
appreciable length over utilities is often prohibited: ~ ~
UTILITIES
Utility information for this study is limited to a few drawings of street improvements as part
of the Expo - Design Center's Dublin Access Plan. Storm drain, sanitary sewer, gas, and
water lines are located within the roadway of Dublin Boulevard. Electrical vaults providing
service to the individual businesses, the traffic control systems and street lighting appear to
be in the sidewalks.
The foundations for the bridge are expected to be outside of the Dublin Boulevard roadway
and sidewalks. Based on the utility information, major utility relocations are not
anticipated. Relocation of some minor utilities is inevitable, however. The costs estimate
contains a monetary placeholder for these unknown relocations.
8 COSTS
Construction and maintenance costs are directly related to the style and quality of the
pedestrian crossing design and the construction. This report does not attempt to characterize
the maintenance costs.
8 Amp for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
? Historically, pedestrian bridges have construction costs ranging from $150 to $2,000 per
~ square foot for the elevated main spans and elevated ramps. Costs for ramps on
embankments can be as low as $80 per square foot. A wide variety of bridge types are
r", included in Appendix A which provide an idea of the possibilities.
As with all projects, the costs do not stop at the bridge and ramp construction. Other costs
r'- include:
r'" · Restoring the areas and facilities disturbed by the construction
~ · Land purchases
· Utility relocations
· Reconstruction of sidewalks and landscaping
· Reconfiguration of traffic controls and signals
· Design and administrative costs
~'~ · Contingency reflecting this early stage of project study
~ · Maintenance and protection of traffic
~.., · Relocating traffic signals
· Additional costs related to relocation of parking spaces for Toys R Us
While the aesthetic quality of a structure can be enhanced through the integration of
r" architectural and structural forms, there is a premium paid for constructing a 'landmark' or
'signature' structure. The higher range of square foot costs covers the extremes of very
~ simple right up through to aesthetically unique designs.
For the purposes of the Dublin Boulevard Pedestrian Bridge, the unit prices selected reflect
the desire to move beyond very simple and look to create a notable bridge that will enhance
the community's sense of pride and ownership.
Design, management and construction costs are likely to range from $3.7 million to $4.5
~-' million. These costs represent an estimate that is based on rules of thumb and not on actual
r-' engineering, design and construction cost estimating efforts. The construction costs should
be taken as 'order of magnitude' costs. Note also that the operating costs of the option
~-, using elevators will create larger annual maintenance costs in servicing the vertical
circulation equipment.
9 NEXT DESIGN AND ENGINEERING STEPS
Should the City of Dublin decide to advance the project, the following planning,
t'~ engineering and architectural efforts are suggested:
r'- · Develop a pedestrian/bicycle circulation plan as part of a specific plan for the area
recognizing the future development of the site at the south end of Golden Gate
~-- Drive and any planned development in the vicinity of the Dublin Boulevard -
Golden Gate Drive intersection
· Based on the potential pedestrian/bicycle circulation demands, review the
r-- pedestrian and vehicular traffic interface at the intersection and determine the need
for a grade-separated pedestrian crossing.
g'~ 9 Amp for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
· Develop complete mapping showing right-of-way, property line, topography,
~.- utilities, and all physical features of the area.
Determine funding sources and approximate project budget
· Engage the City staff and the public in a community design program to jointly craft
r~' the design of a functional and aesthetically appropriate bridge and ramps that are
consistent with the year of construction as well as the future of the area.
· Pothole for specific locations of utilities based on the preliminary design of the
~' facility
~.~ · Complete construction documents for the facility.
· Acquire necessary land or easements.
· Acquire construction permits
· Construct and commission the facility
· Study replacement of Toys R Us parking and determine the relocation needed
10 CONCLUSIONS
A city's infrastructure is a clear and ready statement of a community's commitment to
~ quality of life. Functionality is an essential feature that allows usage. Quality is the mark of
a community's vision that promotes participation and celebration.
Determining the functional necessity of the pedestrian overcrossing of Dublin Boulevard at
Golden Gate Drive is not part of this studv. This study took a very cursory look at the
geometric constraints on the site for placing the overcrossing.
~ Based on this effort, there is a place for the bridge as well as access to the bridge.
Establishments of easements and/or land acquisitions will be required to accommodate the
r-' facility, namely the bank property and relocating the Toys R Us parking on the north side of
Dublin Boulevard. Should the City of Dublin decide to advance the project, the City is
~-' urged to exploit the location of the bridge at the intersection of two major freeways by
~ creating a structure that enhances the City's landscape when viewed from both the sidewalk
and the freeway.
1 0 Amp for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
City of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
A1 PEDESTRIAN BRIDGE EXAMPLES
Salford OUavs, Salfor& UK
Millenium Footbridge, London, UK
Denver Millenium Bridge, Denver, CO
Columbus State Community College
Pedestrian Bridge, Columbus, OH
Watercolor Bridge, Orlando,FL
1 ] Arup for Singer, Fukushima, Evans
Dublin Ped Bridge Report October 24, 2002
Ci~g of Dublin Pedestrian Bridge Over Dublin Boulevard at Golden Gate Drive
Sunderland Footbridge, Sunderlanck UK
River Aire Footbridge, Leeds, UK
Finglassie Footbridge, Glenrothes, UK
Ponte Pedonale, Rome, Italy
Pero's Bridge, Bristol, Avon, UK Pleasant Hill Pedestrian Overcrossing, Pleasant
Hill, CA
Dublin Ped Bridge Report 1 2 Amp for Singer, Fukashima, Evans
· October 24, 2002