HomeMy WebLinkAbout11/01/1988, 11A - TRAFFIC SIGNAL DESIGN MODIFICATIONS p �pMEETING DATE:
CI-W Or SM LUIS OBISPO Nov. 1, 1988
COUNCIL AGENDA REPORT 'TE"'NUMBER:
FROM:
David F. Romero Wayne A. Peterson Prepared by: Barbara Lynch
Public Works Director City Engine Engineering Assistant/Traffic
SUBJECT:
Traffic Signal Design Modifications
CAO RECOMMENDATION:
By Motion Approve the Concept Design of Traffic Signal Modifications as
Submitted by Staff and Approved by ARC.
BACKGROUND:
The engineering division has, over the past five years, pursued the replacement
of the downtown signal controllers. The controllers have been in place since
the mid '50's and '60's and are beginning to cause considerable maintenance
problems. In addition to that, the existing controllers are a potential
liability problem in that they do not provide protection against conflicting
signal indications or flexibility for operation.
Three years ago, Caltrans contacted the city requesting the City's
participation in the installation of an overhead signal at the intersection of
Marsh and Broad Streets. A review of accidents at that intersection indicated
an unusual number of accidents occurring as a result of drivers running the
Marsh Street red light. Engineering placed this request before the Council.
Council agreed to participate in this installation. They directed staff to
schedule the upgrading of other intersections with similar deficiencies, and to
work with the ARC to develop an appropriate design for these installations.
After working with planning staff and the ARC, c fluted style pole, similar to
the street light poles in front of City Hall, wcs chosen for the signal poles
as being most compatible with the character of the downtown. Controller
placement and paint color was also decided.
Engineering felt it would be expeditious to combine the upgrading of the signal
controllers with the upgrading of the traffic signal lights. Following
Council's direction, the other intersections which were scheduled to be
upgraded (see Exhibit "A") were reviewed to det( rmine any deficiencies. In
making this review, the majority of the intersections scheduled to be upgraded
were determined to be below accepted standards. Based on this review, the
installation of mastarms at all downtown intersections not meeting current
standards was pursued (see Exhibit "B") .
64: 1
MY Of San LUIS OBISPO
Worme COUNCIL AGENDA REPORT
Traffic Signal Modifications
Meeting of November 1 , 1988
Page Two.
DISCUSSION:
What are those standards and why do we use them?
To begin with, the U.S. Congress authorized the Secretary of Transportation to
develop standards for Traffic Control Devices and to decree that all traffic
control devices on public streets must be in substantial conformance with these
standards.
The California Vehicle Code, in response to federal law, requires that any
Traffic Control Device which the City installs shall conform to the State
standards (see Exhibit "C") . State standards in turn cover vehicle signal
light placement (see Exhibits "D" and "E").
The standards of visibility use what is called a cone of visibility to
determine the proper location for signal lights (see Exhibit "F,,) . The cone of
visibility is the area viewed by the average motorist when driving down the
street. It encompasses 20 degrees to the left and right of straight ahead.
The standards require that at least one, and preferably two, signal lights be
located in that cone (see Exhibit "G"). If there are no signal lights within
the cone area, drivers may miss seeing the signal. We use these standards to
design all of our new signals and revisions to o:r existing signals.
What happens if we do not follow these standards?
Public safety is the one guiding light when designing traffic control devices
for the public. This involves providing those things necessary to achieve
safety and providing that information to the driver or pedestrian in such a way
that it is seen and understood. The signal design standards are set up to
achieve both of these things. Any time we do not design to accepted standards
we will lose our design immunity, and the burden of proof that we have not
allowed an unsafe condition to exist falls on us. Because of the type and
number of accidents at these intersections, staff feels there is no defendable
basis for deviation from state and federal standards.
If Higuero were to operate as a two-way street it would still require an
overhead signal in each direction. The changes to two-way operation would
require the relocation of three mast arms--one per intersection--across the
intersection, so that they faced oncoming traffic (see Exhibit "H") . It would
also require the addition of some short poles.
OTHER CONCERNS:
For approximately five years Public Works and the Planning Division have worked
hard together to find solutions to address the concerns of providing the right
equipment and meet the aesthetic needs of the downtown. The ARC became
involved in the final design concept decision at-out a year and a half ago.
��►►►���iil�lllll���i ����ll city of san Leis OBISp0
ON A COUNCIL AGENDA REPORT
Traffic Signal Modification
Meeting of November 1 , 1988
Page Three.
In April of 1987, the ARC set out guidelines for the placement of the signal
controllers. In August of 1987, the ARC approved the placement of the
controllers, the color of the controllers and a fluted-style pole design for
mastarm installations.
In an attempt to further reduce the impact of the overhead signal on the
aesthetics of the downtown, the single mastarm design was modified to two
shorter mastarms extending just past the parking strip. This dramatically
improved the view when driving down the street.
FISCAL IMPACT:
The City normally specifies a standard pole for new signal installations.
Because the downtown was considered to be a sensitive aesthetic area, the ARC
required that a special 16-sided fluted pole be used. The relative cost of
this pole is $2250 for a 16-si0ed fluted pole, compared to $700 for a standard
smooth pole. With the isntallation of 17 mostarms it means we are spending
$26, 000 extra to meet aesthetic concerns. In addition, it is estimated that
$40, 000 are being expended in meeting other special requirements of ARC in
order to make the installation as attractive as possible.
CONCLUSION:
The various city departments and the ARC have expended a great deal of effort
over several years and have spared no expense to make this project as
attractive as possible. Staff feels the final product will blend in nicely
with the downtown (see Exhibit "I") and will greatly enhance the safety of our
citizens.
RECOMMENDATIONS:
Staff recommends that the City Council, by motion, approve the traffic signal
modifications as submitted by staff and approved by the ARC.
APPROVED:
City Administrative Officer
City Att ney
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§ 21374 —408— . Div. 11
state agency involved may require the requesting school district to pay an
amount not to exceed 50 percent of the cost of the survey.If it is determined
that such requested protection is warranted,it shall be installed by the city,
county, city and county or state agency involved.
Added Ch. 1443,Stats 1968.Effective November 13,1966
Amended Ch 1061,Stats 1969.Effective November 10,1969.
Directional Markings for roorisls
21374. A local authority may mark or paint the surface of any street or
highway under its jurisdiction,or of any state highway,with the approval of
the Department of Transportation, with lines, arrows, or other suitable
symbols for the purpose of directing visitors and tourists to local points of
interest. No such marking shall be of a color or configuration which, as
determined by the Deparrnent of Transportation, would cause it to be
confused with an official traffic control device.
Added Ch.472,Stan 1976.Effective January 1,1977.
Article 2. Official Traffic Control Devices
Uniform Standards
21400. The Department of Transportation shall,after consultation with
local agencies and public hearings,adopt rules and regulations prescribing
uniform standards and specifications for all official traffic control devices
placed pursuant to this code,including,but not limited to,stop signs,yield
right-of-way signs,speed restriction signs,railroad warning approach signs,
street name signs, lines and markings on the roadway, and stock crossing
signs placed pursuant to Section 21364.
The Department of Transportation shall,after notice and public hearing,
determine and publicize the specifications for uniform types of warning
signs,lights,and devices to be placed upon a highway by any person engaged
in performing work which interferes with or endangers the safe movement
of traffic upon that highway.
Only those sdgns,lights,and devices as are provided for in this section shall
be placed upon a highway to warn traffic of work which is being performed
on the highway.
Any control devices or markings installed upon traffic barriers on or after
January 1, 1984, shall conform to the uniform standards and specifications
required by this section.
Amended Ch.47,Stats 1959.Effective September 18.1959.
Amended Ch.1948,Stats.1961.Effective September 15,1961.
Repealed and added Ch.1033,Stats. 1969. ective November 10,1969.
Amended Ch.988,Stats. 1971.Operative May 3,1972
Amended Ch.545,Stats 1974.Effective January 1,1975.
Amended Ch.487,Stats. 1980.Effective January 1,1981.
Amen
t'v an L 1984.
Conformity to Uniform Standards
21401. Except as provided in Section 21374 onl those official traffic
control devices that conform to the uniform sten az an s eci tcations
_promulgated by the Department of Trgn=rtatini s pace un4n�
street oriTiighwa.
Repealed and added Ch. 1033,Stats 1969.Effective November 10,1969.
Amended Ch 545,Stats 1974.Effective January 1,19M
Amended Ch.472,Stats 1976.Effective January 1,1977.
Article 3. Offenses Relating to Traffic Devices
Offidal Traffic Control Signals
21450. Whenever traffic is controlled by official traffic control signals
showing different colored lights,or colored lighted arrows,successively,one
at a time,or in combination,only the colors green,yellow,and red shall be
EXCERPT FROM CALIFORNIA
VEHICLE CODE
Exhibit "C"
9-20 TRAFFIC SIGNALS AND LIGHTING Traffic Manual
12-1986
The advantages of this operation when compared truck close to the cabinet.
to fully-protected left turn phasing only are: 5. It should not be located in a drainage ditch, in
1. Reduces delay as left turn drivers may have an an area which could be under water or where
opportunity to make their left turns during the subjected to water from sprinklers.
green interval or yellow change interval for 6. It should not obstruct sidewalks, wheelchair
through traffic. ramps, or store entrances.
2. Allows the use of shorter cycle lengths in coor- 7. It should be placed so as not to obstruct pedes-
dinated systems by reducing the time of the trian or driver visibility.
fully protected green interval for the left turn
movement. Keys for the police panel on traffic signal controll-
er cabinets shall be furnished to the California High-
3. way Patrol offices or local enforcement agencies
through lanes as left turn queues are less likely u on re uest.
to exceed the length of the left turn lane.
The following shall apply to permissive left turn 9-24.0 Vehicle Signal Faces and Indications
phasing: Arrangement of vehicle signal faces shall conform
1. This operation should not be used where the left tote Manual on Uniform Traffic
turn accident warrant is satisfied. Normally, each vehicle signal face will consist of at
least three sections. Some of the exceptions are that
2. Normally,signal faces should not be placed in a a single section with a green arrow lens may be used
median facing a left turn lane. to indicate a continuous movement and a 2-section
3. Signs are not required for this operation unless (red, green) face may be used for ramp metering.
U-turns are to be prohibited. Signal lenses shall be a minimum of 8 inches in
4. Conflicting pedestrian signal indications shall diameter. Arrow indications and flashing beacons
display a steady "DONT WALK" or upraised (except those used in ramp metering) shall have
hand while the green arrow is displayed. lenses 12 inches in diameter. Mast arm mounted,
span-wire mounted and signal bridge mounted indi-
There are two sequences that can be utilized with cations should have lenses 12 inches in diameter.
permissive left turn phasing.
9-24.1 Number of Signal Faces
1. Protected-Permissive. With this operation, There shall be at least two signal Faces.for each
left turn traffic is first directed to turn left on the
display of a green arrow and then permitted to turn controlled approach of an intersection including sig-
during the nonprotected interval on the display of a nalized left turn lanes.
circular green.To prevent conflicts at a 4-legged in- Supplemental signal faces should be considered if
tersection, both directions of through traffic should any of the following conditions exist:
be terminated simultaneously. 1. The area is rural.
2. Permissive-Protected. With this operation, 2. The area is urban and the signal is the first one
the left turn traffic is first permitted to turn during on a particular highway.
the nonprotected interval on the display of a circular 3. The roadway is striped for four lanes or more or
green:and then directed to turn left on the display of is wider than 55 feet.
a green arrow. This operation should be used only
where opposing left turns are fully protected or pro- 4. Where visibility of the signal is affected by align-
hibited. ment or obstructions.
9-23.0 Location of Controller Cabinets 9-24.2 Location of Signal Faces
Normally,controller cabinets should be located in On an undivided roadway,the signal faces for each
accordance with the following: through approach of an intersection are usually
1. It should not be vulnerable to traffic. placed at the far right and far left corners.The signal
faces for two or more approaches can often be com-
2. Traffic movements at the intersection should be bined on a single standard.However,where the curb
visible from the controller timing position. return radius is greater than 10 feet,it may be neces-
3. The doors of the cabinet should open away from sary to locate the signal faces on separate standards
the curb or traveled way. to provide maximum visibility for the controlled ap-
proach. Where ad-4;#4 ^' -;-1 r— ^-� -^^•• _,a
4. It should be possible to park a maintenance they may be susl
EXCERPT FROM CALTRANS
TRAFFIC MANUAL
Exhibit "D"
Number and Location of Signal Faces
The placement of the primary signal faces(as specified in Section 413-12
of the MUTCD) is based on visibility requirements. The locational
considerations include lateral and vertical angles of sight toward a signal
face as determined by:
• Typical driver eye position,
• Vehicle design, and
• Vertical, longitudinal, and lateral position of the signal face.
The first two elements are beyond the control of the traffic engineer and
his staff. The third element is a function of the intersection geometry and
may vary widely. Consequently, the geometry of each intersection to be
signalized should be studied individually to determine the optimum
physical layout of the traffic signal indications and to assure that the
signal indication lies within the motorist's vertical and horizontal cone of
vision.
Cone of vision
A driver's vertical vision is restricted by the top of the vehicle's
windshield. This requires that overhead signals be far enough beyond the
stop bar to be viewed by a stopped vehicle(see discussion in 4E-2 Signal
Mounting Considerations).
The lateral location of the face is determined by the driver's cone of
vision and the width of the intersecting cross streets. The MUTCD
requires that at least one (and preferably, two) signal faces be located
within a cone 200 to the left or 20° to the right of the "center of the
approach lanes extended." It should be recognized that this is the
maximum acceptable cone.
In the context of this requirement the cone of vision originates at a
point which represents the center of the approach lanes at the stoo bar-
There is some controversy as to what lanes should be included. For
example, should the center line bisect the entire approach width including
the parking lane and the left-turn lane? Parking lanes should be excluded
if they will not be used as a traffic lane during the service life of the signal
installation. Separate turn lanes should be included unless they are
controlled by separate signal displays.
Figure 4-12 illustrates the maximum cone of vision superimposed on a
two-lane approach with a parking lane and with various width cross-
streets. The figure also defines the critical distances from the stop bar.
This cone would remain the same if a separately-controlled left-turn lane
were added. The cone would shift left 6 feet if a 12-foot wide left-turn
lane, not separately controlled, were added.
Supplemental Signal Indications
The MUTCD requires a minimum of two signal faces for each approach
located on the far side of the intersection. A single indication can be used
4-67
EXCERPT FROM FEDERAL
TRAFFIC MANUAL
(MANUAL ON UNIFORM
TRAFFIC CONTROL DEVICES)
//7f 114? Exhibit "E'
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4-69
EXCERPT FROM FEDERAL
TRAFFIC MANUAL -
CONE OF VISIBILITY
//*4-! Exhibit "F"
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