HomeMy WebLinkAboutItem 8.2 Silvergate Drive Traffic Study (2) I
CITY OF DUBLIN
AGENDA STATEMENT
City Council Meeting Date: October 8, 1990
SUBJECT: Silvergate Drive Traffic Study
(Report by Traffic Engineer Ty Tekawa)
EXHIBITS ATTACHED: Report from TJKM, including Figures
RECOMMENDATION: Consider options presented and direct Staff to proceed
with one or more of the options as follows:
(1) Prepare resolution and schedule public hearing
regarding installation of STOP signs on
Silvergate Drive at Betlen Drive and at Castilian
Road.
(2) Include reconstruction of Silvergate Drive/Dublin
Boulevard intersection in the five-year Capital
Improvement Program, with funding reimbursement
to be provided entirely by developer
contribution.
OR
(3) Refine conceptual median/frontage road plan and
return for City Council and public review at a
future date.
City Staff recommends approval of Alternates (1) and
(2) •
FINANCIAL STATEMENT: Estimated cost of two STOP sign installations,
including striping and advanced warnings, is $2,000,
which would be paid from the Street Maintenance
Operating Budget.
The cost of revising the Dublin Boulevard/Silvergate
Drive intersection is approximately $225,000 and is
proposed to be paid by the developers of the Hansen
Ranch and Donlan Canyon projects.
The cost of the frontage-road concept project would
range from $500,000 to $750,000.
DESCRIPTION:
Following the presentation of a speed survey report several months ago, the
City Council directed Staff to explore possible solutions to the speeding
problems on Silvergate Drive. The City' s traffic engineer, TJKM, has taken a
look at traffic volumes and prevailing speeds and has presented several
options which are described in the attached report. A synopsis of the report
is as follows.
Silvergate Drive is a residential collector street located in the western hill
area. This street' s primary purpose is to provide access to Dublin Boulevard
and to San Ramon Road for residents of a number of existing and future housing
developments. Single-family homes front on Silvergate Drive both south of
Hansen Drive and east of Creekside Drive, creating numerous driveways and a
high demand for on-street parking. Between Hansen Drive and Creekside Drive,
there are only three driveways which enter Silvergate Drive.
-------- ---------------------------------------------
-- -------------------
ITEM N0. COPIES TO: TJKM
Existing average daily traffic (ADT) ranges from 6,200 vehicles per day (vpd)
between San Ramon Road and Peppertree to 2,600 vpd north of Dublin Boulevard.
Traffic volume projections prepared for the West Dublin Planning Area indicate
potential volumes of up to 8,800 vpd west of San Ramon Road and 4,300 to 6,500
vpd on other sections of Silvergate Drive.
For most of Silvergate Drive' s length, there are no raised curb medians.
There are STOP signs at three intersections; however, motorists perceive
Silvergate Drive as a wide, safe roadway with little conflict, and speeds tend
to be higher than the posted 25 mph limit; i. e. , the 85th percentile speed
ranges from 33 to 40 mph.
Following are traffic control devices which were investigated in an attempt to
reduce the speeding problem.
1. Stop Signs
All minor streets entering onto Silvergate Drive are controlled by STOP signs,
with multi-way stops installed at Peppertree Road, Rolling Hills Drive, and
Hansen Drive. Two additional locations for STOP signs were evaluated:
Castilian Road and Betlen Drive.
In terms of speed control, STOP signs have been shown to be effective in
slowing down vehicles within 200 feet of the STOP intersections. Vehicles
tend to increase speed again between the STOP signs. It should also be noted
that regulatory devices such as STOP signs are generally violated when they
are not warranted by sufficient traffic volumes. Side street traffic volumes
at Castilian Road and at Betlen Drive are too low to warrant multi-way STOP
signs, with no overriding conditions such as sight distance problems or
recurring accidents. TJKM does not, therefore, recommend new STOP signs.
2. Speed Humps
Speed humps or undulations, which consist of 12-foot-long asphalt berms placed
across roadways to slow traffic, were evaluated. These humps have a gentler
configuration than the "speed bumps" found in parking lots and can be
traversed at moderate speeds; however, they were ruled out for Silvergate
Drive because of the projected future traffic volumes. Speed humps are
generally used on local streets with traffic volumes not exceeding 3,000 to
4,000 vpd.
3. Roadway Geometrics
Roadway geometrics are physical features designed to facilitate, restrict, or
prevent vehicle movement, such as the raised medians and curb extensions used
on the residential portion of Amador Valley Boulevard. These are intended to
give the driver a feeling that the street is narrow, restricted, and
residential in character, requiring more driving caution and slower speeds.
a. Amador Valley Boulevard Plan
Roadway geometrics were used on Amador Valley Boulevard between Village
Parkway and Stagecoach Road to choke down corners, creating parking bays and
generally narrowing the street. Chokers (curb extensions) were used at the
approaches to this street section and along it at intersections with minor
streets. This street improvement project benefited residents of Amador Valley
Boulevard by creating a landscape opportunity and a more residential character
to the street. The parking bays provide a marginally protected area for
parking and some additional width in the form of a bike lane as a buffer
between the parking and travel lanes. On Amador Valley Boulevard, it was
possible to narrow the median by four feet, which allowed the travel lane to
be moved away from the parking lane and driveways, thus giving the residents
more room to back out.
In 1987, the 85th percentile speed on Amador Valley Boulevard east of Ann
Arbor Way was 33 mph. The 50th percentile speed was 29 mph. The range of
speeds was 20 to 38 mph, and 16% of the vehicles were traveling at or below
the posted 25 mph speed limit. The 1989-90 measured 85th percentile speed was
34 mph (one mph higher) . The 50th percentile speed was 30 mph (one mph
higher) . The range of speeds was 23 to 39 mph, and only 7.4% (8.6% lower) of
the vehicles were traveling at or below the posted speed limit. These results
indicate that the applied geometrics used to constrict Amador Valley Boulevard
have not had an effect on reducing speed.
-2-
b. Conceptual Median Plan
The conceptual median plan presented in the report takes the design an
additional step by using the median and choker features to create one-way
frontage roads.
The primary goal of this plan is to create an environment that is slow and
safe for residents but still serves the collector street function for vehicles
traveling to Dublin Boulevard and to San Ramon Road. The frontage road
concept has been used on Alcosta Boulevard in San Ramon and to an extent on
Stagecoach Road in Dublin.
Figures 2 and 3 of TJKM's report illustrate the frontage road concept on two
sections of Silvergate Drive. Residents would be restricted to one-way
frontage roads with entry and exit areas at the end of the block. Some mid-
block openings could be provided where closures become too long and where an
opening would allow mid-block left- and U-turn maneuvers.
The frontage road is designed to allow a curbside parking lane and a shared
travel lane and bike path. A raised median would separate the frontage road
from the main travel lanes. Some landscaping and/or decorative paving could
be provided.
TJKM's Figure 4 illustrates the plan that would be used between Creekside
Drive and Hansen Drive where very few homes front onto Silvergate Drive.
Frontage roads would not be used in this area, but a 25-foot-wide median is
proposed to separate the--travel lanes.
The primary benefit of this plan is that the residents of Silvergate Drive
would have a "safe road" directly adjacent to their street frontages. The
travel lanes would be visually narrowed, which would permit landscaping and
help soften the environmental perception of residents as traffic volumes
increase. The medians also narrow the travel lanes and reduces the "wide-
and-safe" character of the street.
The drawbacks are the limited access for residents and the fact that reduced
speeds are not necessarily guaranteed. In fact, the through lane speeds will
probably remain the same. The plan concept is to combine medians, striping,
and signing in a manner that discourages higher speeds next to the parking and
driveways and gives the impression that slower speeds are warranted.
4. Reconfigured Intersection at Dublin Boulevard
The intersection of Silvergate Drive at Dublin Boulevard has been approved to
be reconfigured into a standard "T" intersection as part of the impacts from
the Hansen Ranch and Donlon projects. Dublin Boulevard will operate as the
through street, and traffic turning from Silvergate Drive onto Dublin
Boulevard will be required to stop. The existing sweeping curve on the
westbound to northbound right turn will be replaced by a more standard right-
angle curve. This new design will help slow speeds on Silvergate Drive in the
immediate vicinity of this intersection.
The project cost is proposed to be paid for by the developers of the Hansen
Ranch and Donlon projects as mitigation for increased traffic and therefore
will not take place until development has occurred. It is possible that the
City could front the cost of this improvement and recover the cost as
development takes place.
Cost Factors
The total median area proposed to be constructed in the conceptual plan is
approximately 60,000 square feet, the cost of which would be in the
neighborhood of $750,000. The most costly area per foot to develop, however,
would be the area between Creekside Drive and Hansen Drive where few homes
front onto Silvergate Drive. By eliminating the wide landscaped median in
this section from the plan, the total median area to be developed would be
about 38,000 square feet, and the cost could be reduced to approximately
$500,000 without compromising the improvement for the majority of the street
with directly fronting homes.
-3-
Enforcement Alternative
The primary alternative to the median and striping plan is increased and
visible speed enforcement. To date, speed enforcement has been fairly
constant. Over the past year (from September of 1989 through September of
1990) , a total of 269 speeding citations were issued on Silvergate Drive.
TJKM recommends the use of digital readout boards to educate the driver about
speeding tendencies. Even with the use of one or more of the alternatives
presented, TJKM feels that Silvergate Drive will not be consistently safe
unless speed enforcement is present.
At the present time, Police Services has a digital readout board but has not
used it extensively because the board must be used in conjunction with a
manned patrol car. Police Services is unable to dedicate one officer' s time
to operating the board, as all officers on patrol at a given time are needed
to respond to calls. An alternative to the manned patrol car is a specially
equipped trailer which provides solar power for the board. The traffic
officer would then be able to leave the board and provide service to other
areas of the City. The cost of the special radar trailer and associated
equipment is approximately $6,700 to $7,400.
Conclusion
TJKM's primary goal has been to develop concepts that would create a slower
and safer Silvergate Drive for the residents whose homes front onto the
street, while maintaining Silvergate' s efficiency as a collector street.
Staff Recommendation
Staff feels that the traffic "humps" are unsafe for this location, and the
Amador Valley Boulevard plan would not be effective for Silvergate Drive. On
Amador Valley Boulevard, the new design moved the travel lanes toward the
center of the street, allowing more protected room for residents to back out
of their driveways. Silvergate Drive already has an edge stripe which allows
this same amount of space. Since no speed reduction was achieved on Amador
Valley, Staff feels this plan is not cost effective for Silvergate Drive. The
major benefit of the conceptual median plan over the Amador Valley plan is
that residents would be able to back out into a protected "slow" lane instead
of into the existing "fast" travel lane.
The remaining major options presented in TJKM's report are (1) the conceptual
median plan, (2) the reconfigured Silvergate Drive/Dublin Boulevard
intersection, and/or (3) STOP signs at Castilian Road and at Betlen Drive
(which are not recommended by TJKM on the basis of volume warrants) . Staff
recommends that the City Council review the options and provide direction as
to which option(s) should be pursued. It is important to note that TJKM does
recommend continued police enforcement of the speed limit no matter which
options are selected.
Police Services does not recommend the conceptual median plan but does support
additional enforcement and the use of the electronic display board for speed
control.
The Silvergate Drive/Dublin Boulevard intersection is due to be remodeled in
any case; however, if the development of the Hansen Ranch and Donlan Canyon
projects continues to be delayed, the City Council may wish to have this work
performed prior to receiving the developer contributions as a Capital
Improvement Project, with the cost to be reimbursed by the developers in the
future.
If the City Council wishes to pursue the STOP sign option, Staff would prepare
a resolution and schedule a public hearing for the October 29th City Council
meeting.
Given the large cost of the conceptual frontage road plan, coupled with the
drawbacks of limited access for the residents and the lack of guarantee that
speeds would be reduced, City Staff does not recommend that the
median/frontage road plan be pursued at this time, but that the two stop signs
be scheduled for a public hearing and that the City Council direct Staff to
include the Silvergate/Dublin Boulevard "T" intersection into the preliminary
5-Year Capital Improvement Program update for 1991-92 as a developer-
reimbursed project.
-4-
. .a
MEMORANDUM
f �®
C.
September 21, 1990 CjfG. �Q
TO: Lee Thompson V
FROM: Gerri Langtry
SUBJECT: Speed Control on Silvergate Drive
At your direction, TJKM has investigated measures to reduce speeds on Silvergate
Drive. This memo summarizes our study.
Introduction
Silvergate Drive is a residential collector street located in west Dublin with a
purpose to provide access from existing and future residential areas to San Ramon
Road and to Dublin Boulevard. Silvergate Drive varies in width from approximately
85 feet where it intersects with these arterial streets to approximately 65 feet along
its center sections. From Hansen Drive south and from Creekside Drive east, single-
family residential units front onto Silvergate Drive with numerous driveway
openings. Demand for on-street parking is high in these areas. However, Silvergate
Drive's center section, between Creekside Drive and Hansen Drive has very few
homes fronting onto it. This results in few intersection/driveway conflicts and
practically no demand for on-street parking.
Existing average daily traffic (ADT) on Silvergate Drive is shown on the location
map in Figure 1. Existing ADT ranges from 6,200 vehicles per day(vpd) west of San
Ramon Road and east of Peppertree Road to 2,600 vpd north of Dublin Boulevard.
Recent traffic volume projections prepared for the West Dublin Planning Area
indicate potential daily traffic volumes of up to 8,800 vpd west of San Ramon Road
and 4,300 - 6,500 vpd on other sections of Silvergate Drive.
For most of Silvergate Drive's length, there are no raised curb medians. The
existing curb-to-curb street width in all sections is considered wide for a residential
collector street. Although STOP signs exist at three intersections along the street's
route, a driver on Silvergate Drive is given the impression of an ample, safe roadway
with little conflict. As would be expected under these conditions, speeds along
Silvergate Drive tend to be higher than the posted 25 miles per hour (mph) speed
limit.
4637 Chabot Drive,suite 214,Pleasanton,California 94588•(415)463-0611
PLEASANTON-SACRAMENTO-FRESNO-CONCORD
Lee Thompson -2- September 21, 1990
Existing Speed Conditions
Results of a 1989/1990 City Of Dublin radar speed survey on Silvergate Drive are
shown in Table I. Speeds were surveyed at four locations. The results show the
85th percentile speed for Silvergate Drive to be as high as 40 miles per hour north of
Hansen Drive with speeds experienced as high as 51 mph. The median speed
(50th percentile) on Silvergate Drive ranged from 29 mph west of San Ramon Road
to 36 mph north of Hansen Drive. These survey results indicate that the "fastest"
section of Silvergate Drive is between Rolling Hills Drive and Hansen Drive where
very few homes front onto the street. Speeds five to seven mph slower are
experienced along the residential sections of the street.
The 85th percentile is the speed which is exceeded or equalled by 85 percent of the
vehicles in the survey. It is referred to as the "critical speed," and is often used as a
first approximation of a speed limit to be imposed. It is generally felt that at least
85 percent of the drivers operate at speeds which are reasonable and prudent for
prevailing conditions. This would indicate that conditions on Silvergate Drive are
such that drivers feel safe operating at speeds higher than posted even though that
residential properties front onto the street in most areas.
These excessive speeds have prompted recent complaints from existing Silvergate
Drive residents. TJKM Transportation Consultants was directed to evaluate and
recommend alternative speed control devices which would encourage vehicles to
travel at speeds considered safer for a residential street. Due to the variety of
housing, parking and street-width conditions along Silvergate Drive (wide at its end
blocks, narrower in its center sections - houses fronting most sections but separated
by sections without), finding a cohesive speed control solution for Silvergate Drive is
proving to be challenging.
STOP Signs
Several different speed and traffic control devices were researched and evaluated
including STOP signs. All minor streets entering onto Silvergate Drive are
currently controlled by STOP signs. There are also three locations where multi-way
STOP signs are used to stop traffic on Silvergate Drive. They are located at
Peppertree Road, Rolling Hills Drive and Hansen Drive. TJKM was asked to
evaluate two additional locations for STOP signs, one at Betlen Drive and one at
Castilian Road.
In terms of speed control, studies have shown, and it has generally been accepted,
that STOP signs are effective in slowing vehicles down only within a distance of
200 feet from the intersection they control. Vehicles tend to increase speed again
between the next sign. STOP signs would be required every 400 feet to provide
effective speed control.
It should also be noted that regulatory devices such as stop signs are generally
violated when they are not warranted by sufficient traffic volumes. Although
vehicle counts were not performed at the specified Castilian Road and Betlen Drive
intersections, a review of intersection counts taken at other representative
Silvergate Drive locations show that existing traffic volumes approaching from
Lee Thompson -3- September 21, 1990
minor streets to Silvergate Drive are too low to warrant multi-way STOP signs.
There are no overriding conditions such as poor line of sight or a record of recurring
accidents at these locations to consider using STOP signs in absence of sufficient
vehicle volumes.
Speed Humps
Speed humps or street undulations were also considered as a potential speed control
device. Speed humps are an asphalt berm placed across roadways to slow down
vehicles. Unlike the more severe speed bumps often found in private parking lots,
speed humps have a gentler configuration and can be traversed at moderate
traveling speeds. The typical.dimension is 12 feet wide from approach to end with a
three to four inch crest in the center. A speed hump with a three inch height has
been shown to slow the 85th percentile speed to approximately 30 mph in selected
applications on local streets. They have been used successfully in several cities in
California.
Speed humps were ruled out as a viable solution to speeding on Silvergate Drive
primarily due to this street's function as a collector road and due to projected vehicle
volumes resulting from future development in the west Dublin hills. As previously
stated, future volumes on Silvergate Drive are expected to exceed 8,000 vpd in some
sections. To date, speed humps have been tested successfully on local, two-lane
streets where volumes do not exceed 3,000 - 4,000 vpd. To use a program of speed
humps on Silvergate Drive would be "forging new ground" and would require
substantial testing before a recommendation on their use could be made.
Roadway Geometrics
Roadway geometries are physical features designed to facilitate restrict or prevent
vehicle movement. These include features such as the raised medians and curb
extensions (chokers or bulbs) that have been incorporated into the design of Amador
Valley Boulevard between Stagecoach Road and Village Parkway. These are
intended to give the driver a feeling that the street is narrow, restricted, and
residential in character, requiring more driving caution and slower speeds.
Geometries On Amador Valley Boulevard
Roadway geometries on Amador Valley Boulevard between Village Parkway and
Stagecoach Drive were used to choke down the corners, create parking bays and
generally narrow the street. This was accomplished by using chokers at the
approaches to this street section and along it at intersections with minor streets. A
raised center median was developed separating two-way travel. This street
improvement project benefited the residents fronting onto Amador Valley Boulevard
by creating a landscape opportunity and a more residential character to the street.
The parking bays provide a protected area for parking and backing out of driveways.
Regarding vehicle speeds, in 1987, the 85th percentile speed on Amador Valley
Boulevard east of Ann Arbor Way was 33 miles per hour. The 50th percentile speed
was 29 mph. The range of speeds measured was 20 - 38 mph. Sixteen percent
(16 percent) of vehicles were traveling at or below the posted 25 mph speed limit.
Lee Thompson -4- September 21, 1990
The 1989/1990 measured 85th percentile speed was 34 mph. The 50th percentile
speed was measured at 30 miles per hour. The range of speeds measured was
23 - 39 mph. Currently, only 7.4 percent of vehicles on Amador Valley Boulevard
travel at or below the posted 25 mile per hour speed limit. These results indicate
that even over time, the applied geometries used to constrict Amador Valley
Boulevard have not had a significant effect on vehicle speed.
Conceptual Median Plan
The conceptual median and striping plan presented here for Silvergate Drive
incorporates many of the same road narrowing features used along Amador Valley
Boulevard but takes the design an additional step by using these medians and
choker features to create frontage roads for residents on Silvergate Drive.
The primary goal of this plan is to create an environment for Silvergate Drive that is
slow and safe for its residents but that still serves its collector street function for
vehicles traveling to Dublin Boulevard and San Ramon Road. This frontage road
concept has been used locally in the valley on Alcosta Boulevard in San Ramon and
on Stagecoach Road in Dublin.
The frontage road concept on two sections of Silvergate Drive is illustrated in
Figures 2 and 3. Residents fronting onto Silvergate Drive would be restricted to one
way frontage roads with entry and exit areas at the end of the block. Some mid-
block openings could be provided where closures become too long and where an
opening would allow mid-block left and U-turn maneuvers. As Figure 3 shows, in
some areas a frontage road is only required on one side of the street when homes are
not fronting on the other side.
The frontage road is designed to allow a curbside parking lane, and a shared travel
lane and bike path. It would be separated from the main travel way by a raised curb
median. This median is limited in most places to a width of two feet. This width
minimizes the medians landscape potential, but two feet is sufficient to provide
shrubs at ground level or on standards and to incorporate rockscape and decorative
pavement.
The two-way through lanes would be located in the center of the street where
frontage roads are used. It would be an undivided minimum 24-foot wide street as
opposed to its existing 65-foot width. The existing striped turn lane that currently
runs most of Silvergate Drives' length would be removed. Turning movements for
through traffic would be restricted to intersections in most cases.
The street section between Creekside Drive and Hansen Drive would not require a
frontage road treatment since there is a very limited number of homes that front
onto Silvergate Drive in this area. The median design in this area would consist of a
single 25-foot wide median that separates the two travel lanes. Each lane would be
wide enough to accommodate a 12- to 14-foot travel lane and a 6-foot bike lane. This
section of roadway is conceptually illustrated in Figure 4.
Lee Thompson -5- September 21, 1990
Benefits/Restrictions
The primary benefit of this plan is that it provides Silvergate Drive residents with a
"safe road" directly adjacent to their street frontages. It also provides an
opportunity to visually narrow the street. Narrowing has two functions. It creates
an opportunity for limited landscaping. Landscaping in turn will help soften the
environmental perception of residents as vehicle volumes continue to increase (at
high speeds or not) on their street. The medians also narrow the through travel
lanes. This requires two-way through traffic to travel adjacent to each other and
reduces the wide-safe-unimpeded character of Silvergate Drive.
There are primarily two drawbacks to this plan. The first is access. Except at
certain locations, Silvergate Drive residents currently have unlimited access. That
is, they have the ability to enter and exit their properties from two directions. A
frontage road would restrict them to one-way access, although adequate opportunity
to exit the frontage road and make left and U-turns can be incorporated into a
frontage road plan. The second drawback to the frontage road plan is that it does
not guarantee that speeds will be reduced to the posted 25 mph limit, particularly in
the through lanes.
The plan provides an opportunity for residents clustered within frontage road
sections to have more control over the speeds they experience in front of their own
properties; however, the roadway features used do not physically prevent a driver
from traveling at faster speeds. The plan concept is to combine medians, striping
and signing in a manner that discourages higher speeds and gives the impression
that slower speeds are warranted. Unfortunately, such features often must be
accompanied by police traffic enforcement in order to insure success.
Reconfigured Intersection at Dublin Boulevard
The intersection of Silvergate Drive at Dublin Boulevard has been approved to be
reconfigured into a standard T-intersection. Dublin Boulevard will operate as the
through street. Traffic turning from Silvergate Drive onto Dublin Boulevard will be
required to stop. The existing sweeping curve on the westbound to northbound right
turn will be replaced by a more standard near-right angle curve. This new design
will help slow speeds on Silvergate Drive in the immediate vicinity of this
intersection. The approved intersection modification is shown in Figure 5. A
conceptual modification incorporating frontage roads and medians is shown in
Figure 6.
It should be noted that at this intersection, and in other intersections and transition
areas, the conceptual frontage road plan still requires further refinement. The
figures and discussion in this report regarding the frontage road plan are intended
to initiate consideration of the idea. They also show the ability to incorporate this
type of plan onto Silvergate Drive within its existing pavement area.
Cost
The conceptual plan presented in this report would require construction of
approximately 60,000 square feet of raised curb median assumed to be landscaped.
Development of this plan can be accomplished within the existing curb-to-curb width
Lee Thompson -6- September 21, 1990
of Silvergate Drive. The cost of constructing the entire project would be in the
neighborhood of $750,000. The most costly area to develop would be the section
located between Creekside Drive and Hansen Drive where a 25-foot wide landscaped
median is used as a lane divider. Since few homes front onto Silvergate Drive in
this area, sensitivity to vehicle speed in this area is low. It is, however, the "fastest"
section of Silvergate Drive according to the latest speed survey, so attention would
need to be paid to transition areas between this section and the homes fronting the
street in sections to the east and south. If this section were removed from the plan,
the median area to be developed would be reduced to approximately 38,000 square
feet. The cost would be reduced to approximately $500,000.
Alternatives
Although other speed control methods are not recommended in this report, there are
alternatives to this median and striping plan. The primary alternative is increased
speed enforcement. In order to be effective, enforcement would have to be visible
and diligent. New speed posting devices which display individual vehicle speeds on
digital readout boards could be used on a regular basis to educate drivers on
Silvergate Drive about speeding tendencies. Enforcement could be combined with
added STOP signs and the reconfigured intersection at Silvergate Drive and Dublin
Boulevard. However, as previously stated, existing volumes do not warrant
additional multi-way STOP signs at intersections on Silvergate Drive. An
enforcement alternative is less costly than the median and striping concept
presented here, particularly in the short-term. It will not provide Silvergate Drive
residents with a consistently safe street unless enforcement is ever-present.
Conclusion
The primary goal of this speed control study has been to develop a concept that will
create a slower and safer Silvergate Drive for the residents that front onto that
street but that still functions as an efficient collector street for existing and future
vehicles traveling to Dublin Boulevard and San Ramon Road. Towards this goal,
TJKM recommends consideration of a frontage road median and striping plan on
Silvergate Drive. The frontage road concept has been used locally. Although
presented here conceptually, a frontage road plan can be developed within the
existing curb-to-curb width of Silvergate Drive.
Drawbacks include cost, restricting access to existing properties, and the possibility
that vehicle speeds may not be reduced to goal levels particularly in through lanes.
Alternatives include additional stop signs as well as increased speed limit
enforcement. However, after evaluating other speed control methods, the frontage
road concept stands out as appropriate for Silvergate Drive given its various street
section characteristics and the projected future vehicle volumes. If the City of
Dublin so directs, this plan could be refined for more extensive review and possible
presentation to the Silvergate Drive neighborhood.
rhm
157-001
TABLE
SILVERGATE DRIVE
RADAR SPEED SURVEY- DECEMBER 1989& JANUARY 1990
85th 50th
Percentile Percentile 10 mph Range of Existing
Location Speed Speed Pace Speed Speeds Speed Limit
Silvergate Drive
North Of Dublin Boulevard 35 32 27-36 27-38 25
North Of Hansen Drive 40 36 31-40 26-51 25
South Of Rolling Hills Drive 39 35 29-38 26-46 25
West Of San Ramon Road 33 29 24-33 22-40 25
p _ 4'800
l�lc.,'�:1 2,400 "1,700 00-
AVE
2,500 2 000
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0000000 SILVERGATE DRIVE
CONCEPTUAL FIGURE
SILVERGATE DRIVE MEDIAN LOCATION MAP T 1
AND STRIPING PLAN AVERAGE DAILY TRAFFIC J
151-001-8/90-GL
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LEGEND -- ----- r � �
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RAISED MEDIAN _ s
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CONCEPTUAL FRONTAGE ROAD PLAN FIGURE
SILVERGATE DRIVE MEDIAN ROLLING HILLS DRIVE TO T 3
AND STRIPING PLAN WINDING TRAIL LANE
151-001-8/90•GL
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CONCEPTUAL FRONTAGE ROAD PLAN F I G U R E
SILVERGATE DRIVE MEDIAN CREEKSIDE DRIVE TO jr1CAf 4
AND STRIPING PLAN BARNHOLLOW COURT
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CONCEPTUAL APPROVED INTERSECTION PLAN F I G U R E
SILVERGATE DRIVE MEDIAN SILVERGATE DRIVE AT T' 5
AND STRIPING PLAN DUBLIN BOULEVARD
151-001-9/90-GL
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LEGEND
IN
I INCH 1 FEET f
EXISTING CURB
_ RAISED
BIKE LANE
11111 ROSS assussaususum
Stan
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CONCEPTUAL FRONTAGE ROAD PLAN
SILVERGATE DRIVE toy J 33 '< v' 1 •.t`-.
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