HomeMy WebLinkAbout2009-07-06; Traffic Safety Commission; ; Remove shrubs/hedges growing on the southeast comer of Davis Avenue (west) /Knowles Avenue for corner sight visibilityC
CITY OF CARLSBAD
TRAFFIC SAFETY COMMISSION
STAFF REPORT
COMMISSION MEETING OF: July 6, 2009
LOCATION:
INITIATED BY:
Davis Avenue (west) at Knowles Avenue
Robert Richards
2648 Davis A venue
Carlsbad, CA 92008
ITEMNO.6A
REQUESTED ACTION: Remove shrubs/hedges growing on the southeast comer of Davis
Avenue (west) /Knowles Avenue for comer sight visibility.
BACKGROUND:
Staff received a letter (attached) from Mr. Richards asking that shrubs and hedges located
on the southeast comer of Davis Avenue (west) and Knowles Avenue be removed to
provide for comer sight visibility. This intersection is located in the northwest quadrant
of the City of Carlsbad.
DATA:
Davis Avenue intersects Knowles Avenue (see Exhibit 1) at two locations in an "off-set"
intersection configuration ( about 140 feet between the two intersections) that establishes
two separate intersections of Davis A venue (west)/Knowles A venue and Davis A venue
(east)/Knowles Avenue. Both of these intersections with Knowles Avenue are a T-
intersection configuration. The subject intersection is located in an older residential
neighborhood of single family homes between Jefferson Street and Interstate Highway 5.
Davis Avenue (west) is considered the terminating leg/stem of the T-intersection with
Knowles Avenue representing the through street or top of the T-intersection.
Davis Avenue (west)/Knowles Avenue is currently an uncontrolled intersection (does not
have the right-of-way assigned by a yield, stop sign or a traffic signal). Application of
the right-of-way rule requires drivers on the terminating leg (Davis Avenue (west)) to
yield the right-of-way to drivers on Knowles Avenue, the through street.
The single family home at 1095 Knowles A venue is located on the southeast comer of
this intersection and has shrubs/hedges (about 4.5 ft. high) growing at the curb along the
property frontage on both Davis A venue and Knowles A venue. This growth reduces
sight visibility for drivers looking to their right ( east) from Davis A venue (west).
Davis Avenue (west) is not classified on the Circulation Element of the General Plan and
functions as a local residential street. It has a curb-to-curb width of 36 feet. The street
was constructed with rolled curb and gutter, no sidewalk on either side of the street, and
street lights attached to power poles located at the intersections of Davis Place/Davis
C
CITY OF CARLSBAD
TRAFFIC SAFETY COMMISSION
STAFF REPORT
COMMISSION MEETING OF: July 6, 2009
( continued)
ITEMNO. 6A
Avenue (west), Davis Avenue (west)/Laguna Drive, and at the intersection of Davis
Avenue (east)/Knowles Avenue.
Knowles A venue also is not classified on the Circulation Element of the General Plan. It
has a curb-to-curb with of 36 feet with high back curb and gutter, no sidewalk on either
side of the street, and street lights attached to power poles. Knowles A venue has a daily
two-way traffic volume of 438 vehicles between Davis Avenue (west) and Davis Avenue
(east) based on a traffic count on April 30, 2009. A posted speed limit of 25 mph is
found on Knowles A venue.
Field measurements were made to determine the length of existing comer sight distance
available to a driver stopped on Davis Avenue (west) to view vehicles approaching on
Knowles Avenue. Staff found that a northbound driver on Davis Avenue (west) has
about 145 feet of comer sight distance looking to the east on Knowles A venue when the
driver position is 10 feet back from the curb projection on Knowles Avenue. The
measured sight distance is 130 feet less than the standard 7-1/2 second value of comer
sight distance of 275 feet required for a 25 mile per hour-street as specified in the
Caltrans Highway Design Manual Sixth Edition.
The standard comer sight distance provides 7-1/2 seconds for the driver on the crossroad
(Davis Avenue (west)) to complete the necessary maneuver (right or left tum) without
requiring traffic on the through street (Knowles Avenue) to radically alter their speed.
The Caltrans Highway Design Manual also acknowledges that in some cases, where
restrictive conditions exist, the cost to obtain the 7-1/2 seconds of comer sight distance
may be excessive, and a lesser value of comer sight distance may be used. In such cases,
the minimum value for comer sight distance is equal to the stopping sight distance
(copies of sheets 400-7, 8 & 9, & 200-1 of the Caltrans Highway Design Manual are
attached).
At this location, due to the restrictive conditions of the existing shrubs/hedges, 150 feet is
the minimum value used for comer sight distance for these two 25 mile per hour local
streets (150 feet is the stopping sight distance for 25 mph). The 145 feet of measured
sight distance is five feet less than the 150 foot minimum value for comer sight distance
on a 25 mile per hour-street. In addition, comer sight distance increases looking to the
east as drivers on Davis Avenue (west) move forward and closer to Knowles Avenue.
The comer sight distance is limited looking to the east from Davis Avenue (west) by the
shrubs/hedges growing near the southeast comer at 1095 Knowles Avenue (see Exhibit
2).
Due to the small reduction in comer sight visibility, based on driver position, and the fact
this intersection is uncontrolled, staff also field measured the distance for the safe
approach speed to the intersection. This measurement was conducted as the installation
of a stop sign may warrant consideration on the terminating leg/stem of a T-intersection
C
CITY OF CARLSBAD
TRAFFIC SAFETY COMMISSION
STAFF REPORT
COMMISSION MEETING OF: July 6, 2009
( continued)
ITEMNO. 6A
when the safe approach speed to the intersection for a driver on the terminating leg is less
than 10 miles per hour due to visibility limitations. A driver on the terminating leg of a
T-intersection, when traveling towards the intersection, reaches a decision point where it
is necessary to determine if braking to a stop is required because of a vehicle approaching
on the through street may constitute a conflict. The location of the decision point on the
terminating leg must allow the driver sufficient distance to view, to both the driver's right
and left, all approaching vehicles on the through street. The driver on the terminating leg,
generally not having the right-of-way, can then initiate actions to slow, stop, or avoid a
conflict with other vehicles, as necessary, when the required minimum clear sight triangle
distances are provided (see Exhibit 3).
For local streets, the terminating leg (minor street) decision point is assumed to be 50 feet
from the intersection conflict point when the vehicle on the minor street has an approach
speed of 10 miles per hour. The design speed for a local street is 25 miles per hour as
specified in the Carlsbad Engineering Department Design Standards.
A distance of 150 feet (stopping sight distance for 25 miles per hour in accordance with
the Sixth Edition of the Caltrans Highway Design Manual) along the through street must
be provided to drivers on the terminating leg to view vehicles approaching the
intersection. Installation of a stop sign is considered to positively assign the right-of-way
if a vehicle on the through street cannot be seen at the point of its minimum stopping
sight distance from the intersection conflict point when a driver on the terminating leg is
at the decision point. Field measurements found that at the decision point a northbound
driver on Davis Avenue (west) has sight visibility limited to approximately 80 feet when
looking east for approaching westbound vehicles on Knowles A venue. Looking to the
west, a northbound driver on Davis Avenue (west) has sight visibility limited to
approximately 66 feet. Line of sight limitations on the southeast comer of the
intersection result from the shrubs/hedges at the curb and extending along the property
frontage on Davis A venue and Knowles A venue. Line of sight limitations on the
southwest comer of the intersection are due to shrubs growing near the comer on
Knowles A venue.
CONCLUSION:
In summary, a driver stopped on Davis Avenue (west) has about 145 feet of comer sight
distance looking to the east on Knowles A venue, which is five feet less than the 150 foot
minimum value specified for comer sight distance on a 25 mile per hour-street where
restrictive conditions exist.
However, field measurement of the distances for the safe approach speed to the
intersection were found to be substantially less than the 150 feet required to be provided
along the through street (from the decision point on Davis Avenue (west) a driver has
sight visibility limited to approximately 80 feet looking to the east, and approximately 66
CITY OF CARLSBAD
TRAFFIC SAFETY COMMISSION
STAFF REPORT
COMMISSION MEETING OF: July 6, 2009 ITEMNO. 6A
( continued)
feet to the west). Consequently, the 10-mile per hour safe approach speed to the
intersection is not being met for drivers on Davis Avenue (west) to view approaching
vehicles on Knowles A venue. Therefore, installation of a yield or a stop sign can be
considered on Davis Avenue (west) to address the line of sight limitations.
It should be noted that significant shrub/hedge removals would be required at the
intersection on both the southeast and southwest corners to increase the line of sight
distances in both directions to provide a 10-mile per hour safe approach speed on Davis
Avenue (west) at Knowles Avenue.
RECOMMENDATION:
To address reduced sight distance at this intersection, the Traffic Safety Coordinating
Committee recommends:
• Installation of a STOP sign on Davis Avenue (west) at its intersection with
Knowles A venue.
• Do not remove any shrubs or hedges on either corner.
• Send a letter to the resident at 1095 Knowles A venue requesting that they trim
the hedges along their property frontage on Davis Avenue (west) and Knowles
Avenue back vertically to the back of the rolled concrete curb.
NECESSARY CITY COUNCIL ACTION:
The City Council must adopt an ordinance to establish the stop control on Davis A venue
(west) via installation of a stop sign, as recommended.
RECEIVED
APR o 1 2009
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CATION MAP
BUENA
VISTA
LAGOON
,-: "'
LEGEND:
,----.. I I
I I = PROJECT LOCATION
BUENA PL
KNOWLES A 1/f..
G) = PROPOSED STOP SIGN
~ = EXISTING STOP SIGN
YOURELL AV£.. l
BUENA VISTA WY.
PROJECT NAME INTERSECTION OF
DAVIS AVENUE (WEST)/ KNOWLES AVENUE
H:\Transportation\AutoCAD\Rehfeldt\Location Maps\Davis Ave-Knowles-ex.1
NTS
EXHIBIT
1
1-
KNOWLES
AVENUE
---------275' (7-1/2 SECOND) -----: I
150' REQUIRED • 1 ·~....1··',1
----145' ACTUAL----~•! ~
(MEASURED) -~1 ~
CURB PROJECTION
--=----_":---. ____ T ------~~.._..----.c....~~__.....,::::::.-
10·
TITLE
_l_.1..--_-i
DRIVER/
POSITION
SHRUBS/HEDGES
~4.5 FT. HIGH
1095 KNOWLES A VE.
SHRUBS/HEDGES
~4.5 FT. HIGH
NOTE: FIELD MEASUREMENTS
OBTAINED ON 04/21/09
DAVIS AVENUE (WEST)/ KNOWLES AVENUE
EXISTING CORNER SIGHT DISTANCE
H:\Transportation\AutoCAD\Rehfeldt\Location Maps\Davis Ave-Knowles-ex.2C
~I
IXl1
I
NTS
EXHIBIT
2
KNOWLES
AVENUE
------150' REQUIRED-------'• I
CONFLICT POINT~ ~ i-------80' ACTUAL
(MEASURED)
T
NTS
NTS
TITLE
50'
DECISION POINT/
\.EQUIRED LINE
OF SIGHT
SHRUBS/HEDGES
~4.5 FT. HIGH
1
150' REQUIRED
• 66' ACTUAL---~
/
CONFLICT POINT
REQUIRED LINE
OF SIGHT
(MEASURED)
T
50'
SHRUBS/HEDGES
~4.5 FT. HIGH
NOTE: FIELD MEASUREMENTS
OBTAINED ON 04/21/09
KNOWLES
AVENUE
NOTE: FIELD MEASUREMENTS
OBTAINED ON 04/21/09
SHRUBS/HEDGES
~4.5 FT. HIGH
DAVIS AVENUE (WEST)/ KNOWLES AVENUE
INTERSECTION APPROACH SIGHT TRIANGLE
EXHIBIT
3
H:\Transportation\AutoCAD\Rehfeldt\Location Maps\Davis Ave-Knowles-ex.3B
C
IDGHWAY DESIGN MANUAL 400-7
September 1, 2006
404.3 Turning Templates
(I) General. The truck-turn template is a design
aid for locating the wheel paths of large
vehicles as they turn through at-grade
intersections. Consideration should be given to
the overhang of the truck, where the body of
the truck slightly extends (approximately
2 feet) beyond the wheel path. The template is
useful for dete.lJJljning comer radii, for
positioning island noses, and for establishing
clearance to bridge piers, signal poles, and
other hardware at intersections. Templates can
help determine the width of a channeled
separate turning lane, Topic 407 illustrates
scaled turning templates for the various design
vehicles and turning radii.
(2) STAA Truck. The STAA truck-turn templates
should be used in the design of all new
interchanges and intersections on the National
Network and on routes leadins from the
National Network to designated service and
terminal routes. On rehabilitation projects they
should be used at interchanges and
intersections proposed as service or terminal
access routes. In some cases, factors such as
cost, right of way, environmental issues, local
agency desires, and the. type of community
being served may limit the use of the ST AA
templates. In those cases, other . appropriate
templates should be used.
The minimum practical turning radius is 50
feet. However, the 60-foot radius develops
less swept width and may have an advantage.
The 60-foot radius should be used in most
situations, but the 50-foot radius is acceptable
in restricted situations.
(3) California Truck. The California truck-tum
template should be used in the design of
highways not on the National Network. The
minimum practical turning radius is 50 feet.
(4) Bus. At intersections where truck volumes are
light or where the predominate truck traffic
consists of mostly 3-axle and 4-axle units, the
bus turning template may be used. Its wheel
paths sweep a greater width than 3-axle
delivery trucks and the smaller buses such as
school buses, but a slightly lesser width than a
4-axle truck.
Topic 405 -Intersection Design
Standards
405.1 Sight Distance
(1) Stopping Sight Distance. See Index 201.1 for
mjnimum stopping sight distance requirements.
(2) Comer Sight Distance.
(a) General--At unsignalized intersections a
substantially clear line of sight should be
maintained between the driver of a vehicle
waiting at the crossroad and the driver of
an approaching vehicle.
Adequate time must be provided for the
waiting vehicle to either cross all lanes of
through traffic, cross the near lanes and
tum left, or tum right, without requiring
through traffic to radically alter their
speed.
The values given in Table 405. lA provide
7-1/2 seconds for the driver on the
crossroad to compJete the necessary
maneuver while the approaching vehicle
travels at the assumed design speed of the
main highway. The 7-1/2 second criterion
is normally applied to all lanes of through
traffic in order to cover all possible
maneuvers by the vehicle at the crossroad.
However, by providing the standard corner
sight distance to the lane nearest to and
farthest from the waiting vehicle, adequate
time should be obtained to make the
necessary movement. On multilane
highways a 7-1/2 second criterion for the
outside lane, in both d.irections of travel,
normally will provide increased sight
distance to the inside Janes. Consideration
should be given to increasing these values
on downgrades steeper than 3 precent and
longer than 1 mile (see Index 201.3),
where there are high truck volumes on the
crossroad, or where the skew of the
intersection substantially increases the
distance traveled by the crossing vehicle.
C
400-8 HIGHWAY DESIGN MANUAL
September 1,2006 ------------------------------------
In determining corner sight distance, a set
back distance for the vehicle waiting at the
crossroad must be assumed. Set back for
the driver on the crossroad shall be a
minimum of 10 feet plus the shoulder
width of the major road but not less
than 15 feet. Corner sight distance is to be
measured from a 3.5-foot height at the
location of the driver on the minor road to
a 4.25-foot object height in the center of
the approaching lane of the major road. If
the major road has a median barrier, a
2-foot object height should be used to
determine the median barrier set back.
In some cases the cost to obtain 7-1/2
seconds of comer sight distances may be
excessive. High costs may be attributable
to right of way acquisition, building
removal, extensive excavation, or
unmitigable environmental impacts. In
such cases a lesser value of comer sight
distance, as described under the following
headings, may be used.
(b) Public Road Intersections (Refer to Topic
205)--At unsignalized public road
intersections (see Index 405.7) corner sight
distance values given in Table 405.IA
should be provided.
At signalized intersections the values for
comer sight distances given in Table
405. lA should also be applied whenever
possible. Even though traffic flows are
designed to. move at separate times,
unanticipated vehicle conflicts can occur
due to violation of signal, right turns on
red, malfunction of the signal, or use of
flashing red/yellow mode.
Where restrictive conditions exist,
similar to those listed in Index
405.1(2)(a), the minimum value for
corner sight distance at both signalized
and unsignalized intersections shall be
equal to the stopping sight distance as
given in Table 201.1, measured as
previously described.
( c) Private Road Intersections (Refer to Index
205.2) and Rural Driveways (Refer to
Index 205.4)--The minimum corner sight
distance shall be equal to the stopping
sight distance as given in Table 201.1,
measured as previously described.
(d) Urban Driveways (Refer to Index 205.3)-
Comer sight distance requirements as
described above are not applied to urban
driveways.
(3) Decision Sight Distance. At intersections
where the State route turns or crosses another
State route, the decision sight distance values
given in Table 201 7 should be used In
computing and measuring decision sight
distance, the 3.5-foot eye height and the
0.5-foot object height should be used, the
object being located on the side of the
intersection nearest the approaching driver.
The application of the various sight distance
requirements for the different types of
intersections is summarized in Table 405. IB.
(4) Acceleration Lanes for Turning Moves onto
State Highways. At rural intersections, with
stop control on the local cross road,
acceleration lanes for left and right turns onto
the State facility should be considered. At a
minimum, the following features should be
evaluated for both the major highway .and the
cross road:
• divided versus undivided
• number of lanes
• design speed
• gradient
• lane. shoulder and median width . traffic volume and composition . turning volumes . horizontal curve radii
• sight distance
• proximity of adjacent intersections
• types of adjacent jntersections
For additional information and guidance, refer
to AASIITO, A Policy on Geometric Design of
Highways and Streets, the Headquarters Traffic
Liaison and the Design Coordinator.
IDGHW A Y DESIGN MANUAL 400-9
September 1, 2006
Table 405.1A
Corner Sight Distance
(7-1/2 Second Criteria)
Design Speed
(mph)
25
30
35
40
45
50
55
60
65
70
Comer Sight
Distance (ft)
275
330
285
440
495
550
605
660
715
770
Table 405.1 B
Application of Sight Distance
Requirements
Intersection Sisht Distance
Tl'.Ees Stoeeins Comer Decision
Private Roads X xi)
Public Streets and X X
Roads
Signalized X (2)
Intersections
State Route Inter-X X X
sections & Route
Direction
Changes, with or
without Signals
(]) lfaing l!iopp.ing mgbt diinanoo 111:tw(;rn llJl eyo bcight of3,5 ft l!lld llll
object height of 4.25 ft. See Index 405.1(2Xa) for setback
requirements.
(2) Apply rorncr sight distance requirements at signalized intersections
whenever possible due to unanticipated violations of the signals or
malfunctions of the signals. See Index 405.1 (2Xb ).
405.2 Left-tum Channelization
(I) General. The purpose of a left-tum lane is to
expedite the movement of through traffic,
control the movement of turning traffic,
increase the capacity of the intersection, and
improve safety characteristics.
The District Traffic Branch normally
establishes the need for left-tum lanes. See
"Guidelines for Reconstruction of
Intersections," August 1985, published by the
California Division of Transportation
Operations.
(2) Design. Elements.
(a) Lane Width --The lane width for both
single and double left-turn lanes on
State highways shall be 12 feet. Under
certain circumstances (listed below), left-
tum lane widths of 11 feet or as narrow as
10 feet may be used on RRR or other
projects on existing State highways and on
roads or streets under other jurisdictions
when supported by an approved design
exception pursuant to Index 82.2. When
considering lane width reductions adjacent
to curbed medians, refer to Index 303.5 for
guidance on effective roadway width;
which may vary depending on drivers'
lateral positioning and shy distance from
raised curbs.
• On high speed rural highways or
moderate speed suburban highways
where width is restricted, the minimum
width of single or dual left-tum lanes
may be reduced to 11 feet.
• In severely constrained situations on
low to moderate speed urban highways
where large trucks are not expected,
the minimum width of single left-tum
lanes may be reduced to 10 feet. When
double left-tum lanes are warranted
under these same circumstances the
width of e@b lane shld1 be no less than
I I feet. This added width is needed to
assure adequate clearance between
turning vehicles.
IDGHW A Y DESIGN MANUAL 200-1
September I, 2006
CHAPTER200
GEOMETRIC DESIGN AND
STRUCTURE STANDARDS
Topic 201 -Sight Distance
Index 201.1 -General
Sight distance is the continuous length of highway
ahead visible to the driver. Four -types of sight
distance are considered here: passing, stopping,
decision, and comer. Passing sight distance is used
where use of an opposing lane can provide passing
opportunities (see Index 201.2). Stopping sight
distance is the minimum sight distance to be
provided on multilane highways and on 2-lane
roads when passing sight distance is not
economically obtainable. Stopping sight distance
also is to be provided for all elements of
interchanges and intersections at grade, including
private road connections (see Topic 504, Index
405.1, & Figure 405.7). Decision sight distance is
used at major decision points (see Indexes 201.7
and 504.2). Corner sight distance is used at
intersections (see Index 405.1, Figure 405.7, and
Figure 504.3J).
Table 201.1 shows the standards for stopping
sight distance related to design speed, and these
shall be the minimum values used in design.
Also shown are the values for use in providing
passing sight distance.
Chapter 3 of "A Policy on Geometric Design of
Highways and Streets," AASHTO, contains a
thorough discussion of the derivation of stopping
sight distance.
201.2 Passing Sight Distance
Passing sight distance is the mm1mum sight
distance required for the driver of one vehicle to
pass another vehicle safely and comfortably.
Passing must be accomplished assuming an
oncoming vehicle comes into view and maintains
the design speed, without reduction, after the
overtaking maneuver is started.
Table 201.1
Sight Distance Standards
Design Speed(!) Stopping(2) Passing
(mph) (ft) (ft)
20 125 800
25 150 950
30 200 l,100
35 250 1,300
40 300 1,500
45 360 1,650
50 430 1,800
55 500 1,950
60 580 2,100
65 660 2,300
70 750 2,500
75 840 2,600
80 930 2,700
(l) See Topic 101 for selection of design speed.
(2) For sustained downgrades, refer to advisory standard in
Index 201.3
The s1ght rustance available for passing at any
place is the longest distance at which a driver
whose eyes are 3 feet ½ inch above the pavement
surface can see the top of an object 4 feet ¼ inch
high on the road. See Table 20 U for the
calculated values that are associated with various
design speeds.
In general, 2-lane highways should be designed to
provide for passing where possible, especially
those routes with high volumes of trucks or
recreational vehicles. Passing should be done on
tangent horizontal alignments with constant grades
or a slight sag vertical curve. Not only are drivers
reluctant to pass on a tong crest vertical curve, but
it is impracticable to design crest vertical curves to
provide for passing sight distance because of high
cost where crest cuts are involved. Passing sight
distance for crest vertical curves is 7 to 17 times
longer than the stopping sight distance.
Ordinarily, passing sight distance is provided at
locations where combinations of alignment and