HomeMy WebLinkAbout1988-09-12; Traffic Safety Commission; ; Establish a Guardrail Evaluation PolicyCITY OF CARLSBAD
TRAFFIC SAFETY COMMISSION
COMMISSION REPORT OF: September 12, 1988 ITEM NO._§_Q_
LOCATION: City Wide
INITIATED BY: City Engineer
REQUESTED ACTION: Establish a Guardrail Evaluation Policy
BACKGROUND:
DATA:
A Guardrail Priority Li st has never been established in the City of
Carlsbad. This report will provide the mechanism needed to evaluate and
compare potential accident locations for guardrail installation.
On March 12, 1987 Alan Reece requested the City of Carlsbad to install a
roadside barrier on the west side of Rancho Santa Fe Road between La Costa
Avenue and Cadencia Street. This item was discussed at the Traffic Safety
Coordinating Committee (TSCC) on April 27, 1987. The Committee recommended
initiating a guardrail priority list to be reviewed by the Traffic Safety
Commission. On May 4, 1987 the Traffic Safety Commission adopted the TSCC
recommendations and this matter was placed in the 1988 work program for
the Traffic Engineering Division.
The attached report is submitted for review and evaluation by the Traffic
Safety Commission. Establishing the guardrail priority list from the
evaluation criteria will assist in selecting projects to be authorized into
future Capital Improvement Program budgets. This evaluation criteria and
priority list will be a tool to directly evaluate traffic requests for new
guardrail installations when received from the public.
At the time a guardrail location is chosen from the priority list to be
a future installation, a detailed engineering design will be required to
identify the exact length of guardrail and exact locations of the beginning
and end. The lengths listed on the guardrail priority list are approximate
and are for estimating purposes only.
RECOMMENDATION:
The Traffic Safety Coordinating Committee recommends the Traffic Safety
Commission review, evaluate and suggest changes, as necessary, to the
attached Guardrail Evaluation Policy.
TRAFFIC SAFETY COMMISSION
COMMISSION REPORT OF: September 12, 1988
(Continued)
NECESSARY CITY COUNCIL ACTION:
No City Council action is required.
ITEM NO. 6D
GUARDRAIL EVALUATION
POLICY
PREPARED BY:
ENGINEERING DEPARTMENT
Traffic Engineering Division
AUGUST 1988
Introduction .
Background and Purpose
General. .
Procedure.
Data ...
Results and Conclusion
CITY OF CARLSBAD
Engineering Department
Traffic Engineering Division
Guardrail Evaluation Policy Report
August 1988
Table of Contents
List of Figures
Figure 1 -Guardrail Evaluation Worksheet.
Figure 2 -Guardrail Priority List ....
Figures 4-7 -1987 Guardrail Investigation Locations
List of Tables
Page
1
I
2
2
5
6
4
7
. ... • ... 8 -11
Table I -Streets Included in Study ..................... 12
Appendix
A. Figure 7-1 -CALTRANS -Equal Severity Curve
B. Figure 7-2 -AASHTO -Roadside Hazard Warrants
C. Table 7-2 -AASHTO -Additional Warrants
INTRODUCTION
CITY OF CARLSBAD
Traffic Engineering Division
Guardrail Evaluation Policy
Carlsbad i s a coasta 1 community 1 ocated in northern San Di ego County,
approximately 30 miles north of downtown San Diego. It is a moderate si zed City
having a popu lation of approximately 60 ,000 within an area of app roximately 35
square miles.
The City has a roadway netwo r k totaling 198 mi 1 es . This network is
comp r ised of 55 miles of arterial streets and 143 miles of collector and/or local
streets. The arterial streets can be further classified into 21 miles of prime,
12 miles of maj or and 22 miles of secondary arterial streets. Potential
guardrail locati ons on the arterial street system is the focus of this report .
Evaluat ion s of locations for future installations of guardrail are
initiated in seve ral ways: at the request of a resident, by the conditions of
approval for a development project, by staff observation and study of changes
in roadway co nditions or by monitoring accident history. Private developments
will be evaluated for guardrails by the project engineer in the Engineering
Department th at is assigned to the project.
BACKGROUND AND PURPOSE
Before i nitiating the installation of new guardrail, a determination must
be made as to the accident potential for a location and how it compares with all
other locations throughout the City. Primarily as a result of a constantly
changing roadway network and increases in t r affic volumes within the City of
1
Carlsbad, potentially hazardous locations will continue to be of increasing
concern.
A guardrai l inventory of existing installations was conducted to identify
substandard and/or damaged guardrail . Data was collected that included the type,
location, length , and general condition of each existing guardrail installation.
This study was conducted to establish a comprehensive 1 i st of roadway
segments in t he City where it would be less severe for a vehicle to impact a
guardrail than for the vehicle to leave the travelled roadway, such as the
typical run off the road type of accident.
GENERAL
Longitudinal barriers, generally called guardrails, are installed to reduce
the severity of "run-off-road " accidents. Guardrails are used to deflect a
vehicle away f rom an embankment slope or fixed object and to dissipate the energy
of a str aying ve hicle.
Basically, the three types of guardrail are rigid, semi -rigid and flexible.
Rigid guardrai ls are installed only whe r e there is no tolerance for deflection . .
This type is used primarily to separate two -direction flow of traffic on high
speed faciliti es where the deflection into the opposing traffic could result in
collisions. Sem i -rigid guardrails will deflect up to six feet, thus greatly
reducing acciden t severity. It is used in locations where there is tolerance
for significant deflection of the guardrail. Flexible guardrails are rarely used
except where l arge clear zones exist. This study focuses on semi -rigid guardrail
applications.
PROCEDURE
This study consisted of a three phase program . First, a guardrail
evaluation wo rksh eet was prepared. Prior to des i gning the guardrail evaluation
2
worksheet, staff contacted various cities between Los Angeles and San Diego as
to criteria th os e cities use. It was found that none of the contacted agencies
have a forma l guardrail evaluation worksheet. Many cities identified the
specific reference or references used to analyze requested guardrail locations.
The two referenc es most often used are documents prepared by the California
Department of Tr ansportation (CALTRANS) and the American Association of State
Highway and Transportation Officials (AASHTO). Each of these agencies publish
guidelines for the selecti on, location, and design of guardrails. The City of
Carlsbad guardra il evaluation worksheet was derived from both references, using
qualitative guidelines to assign a quantitative point system.
The second phase of the program consisted of staff field surveying each
arterial street and identifying potential guardrail locations. Pertinent
engineering info rmation for each location was documented.
The thi rd and final phase of the program consisted of an office evaluation
of all assemb led data, including:
1. Acci dent frequency information for 1987.
2. Ro adway volumes and number of lanes during the same year.
3. De fl ection angles for each curve.
4. Do wn grades greater than 2 percent.
After al l variables are identified on the evaluation worksheet, points are
totaled and ra nk ing is assigned.
3
GUARDr ",IL EVALUATION wi :KSHEET
LOCATION: DATE: ___ _
EVALUATED BY: DIRECTION OF TRAVEL :
# 1 EMBANKMENTS
Maximum height of embankment
#2 ROADSIDE HAZARDS
FIXED OBJECT _ Size
MEETS CAL TRANS WARRANTS
(see figure 7-1)
Slope -in degrees below the horizon
MEETS AASHTO WARRANTS
(see figure 7-2)
Distance from the
edge of the travel way
NONTRAVERSABLE HAZARD _ Slope to object or hazard
#3 ACCIDENT FREQUENCY
NUMBER OF RUN-OFF-ROAD ACCIDENTS =--= (N)
PROPERTY DAMAGE ONLY
Accidents on the outside of a curve
YES= 1
NO= 0
YES= 1
NO= 0
NX1=
INJURY OR FATALITY N x 2 =
PROPERTY DAMAGE ONLY (N-1) x 1 =
Accidents on a tangent or inside of a curve
INJURY OR FATALITY (N-1)x2=
#4 CURVES DEFLECTION ANGLE =
Are curve warning signs posted
Downgrade greater than 2 percent
#5 ROADWAY VOLUMES
YES= 0.30
YES = 0 .25
Average daily traffic = __ _ = A.D.T.
= (n) Total number of lanes = __
Approximate Guardrail Length
FIGURE 1
A
= (D) D x 0.01 =
NO= 0.00
NO= 0.00
A .D.T.
n X 15000
TOTAL SCORE
=
DATA
To quantitatively evaluate each guardrail location, staff developed the
guardrail evaluation worksheet (Figure l} previously discussed. This worksheet
is a combination of various methodologies used by other agencies.
The worksheet is comprised of five parts as described below.
I. Embankments
Primary contributors to embankment accident severity are the slope and
height of the embankment. The California Department of Transportation (CALTRANS}
has developed Figure 7-1 (see Appendix}, as an aid in determining whether a
guardrail will decrease or increase the severity of run-off-road accidents.
II. Roadside Hazards
Roadside hazards consist of both fixed object and non-traversable hazards.
Factors considered in the potential severity of an accident involving fixed
objects and nontraversable hazards are the distance from the travel way and the
prevailing speed of vehicles on the roadway. Other considerations include the
grade (%} between the roadway and the hazard, and the size and type of hazard
(see Appendix}.
III. Accident Frequency
Accident records are researched to determine if there is a history of a
certain pattern of accidents for a particular section of roadway. Run-off-road
ace i dents are noted and a copy of the ace i dent report is included with the
evaluation worksheet. This section of the evaluation can confirm potential
ace i dent locations by i dent ifyi ng where a driver has al ready encountered a
problem.
5
IV. Cu rves
The defl ection angle of each roadway section under investigation is noted
and used to incrementally rank potential accident locations . The longer a
vehicle continues to turn, the greater the potential for accidents. The
worksheet gives special consideration to roadway curvatures that have substandard
geometrics. At locations where curve warning signs have been posted to warn
vehicles to redu ce speed below the posted speed limit, the potential for problems
increases. Add itional evaluation points are given to curves on down-grades of
more than 2 percent.
V. Roadway Volumes
Roadway volumes are an important factor used to determine the exposure
potential of a roadway section. As volumes increase on a roadway section, the
probability of an accident increases. The number of lanes in each direction will
be used to determine approximately the volume in the lane closest to the roadway
hazard .
RESULTS AND CONC LUSION
A total of 60 locations were evaluated and assigned a point score. A list
of 33 of these l ocations are indicated on Figure 2, ranking the locations from
highest to lowest priority. The other 27 locations do not meet by either
CALTRANS or ASSHTO warrants. Figures 4 through 7 show the warranted locations
inventoried fo r 1987. Table I is a list of streets surveyed for the same year.
In order t o qualify for the guardrail priority list, each location must
warrant a gua rdrail installation under either the CALTRANS embankment warrants
AASHTO roadside hazard warrants . The guardrail priority list will be used to
aid in schedul i ng future capital improvement programs. Also, if any public
requests for new guardrail are received, staff has the mechanism needed to
evaluate and ran k each request.
6
GUA tRAIL PRIORITY _IST
RANK LOCATION POINTS LENGTH
1 EL CAMINO REAL APPROX . 1.1 Ml. N/0 FARADAY AVENUE 3.74 250'
2 ALGA ROAD APPROX . 0.15 MI. W/0 ALICANTE ROAD 2.86 450'
3 TAMARACK AVENUE APPROX . 0.3 MI. W/0 EL CAMINO REAL 2.64 425'
4 ALGA ROAD APPROX . 0. 4 MI . E/0 ALICANTE ROAD 2.59 350'
5 CARLSBAD BOULEVARD APPROX . 0.06 Ml . S/0 STATE STREET 2.47 100'
6 CARLSBAD BOULEVARD N/0 MOUNTAIN VEIW DRIVE 2.47 50'
7 MARRON ROAD APPROX. 0 .1 Ml. W/0 AVENIDA DE AN ITA 2.40 350'
8 MONROE STRE ET APPROX. 0.2 Ml. S/0 MARRON ROAD 2.38 75'
9 LA COSTA AV ENUE APPROX . 0. 6 Ml. W/0 EL CAMINO REAL 2.38 1300'
10 JEFFERSON STREET N/0 BUENA VISTA CREEK 2.33 200'
11 EL FUERTE STREET APPROX . 0. 6 Ml. N/0 CORTE DE LA VISTA 2.31 625'
12 ELM AVENUE E/0 VICTORIA AVENUE 2.17 450'
13 EL CAMINO REAL APPROX . 0.4 Ml. N/0 FARADAY AVENUE 2.14 200'
14 ALGA ROAD W/0 CAZADERO DRIVE 1. 96 1325'
15 EL FUERTE STREET APPROX . 0.15 Ml. N/0 ALGA ROAD 1.93 225'
16 PALOMAR AIRPORT ROAD APPROX . 0.3 Ml . W/0 EL FUERTE STREET 1.84 950'
17 JEFFERSON STREET S/0 CARLSBAD CITY LIMI T 1. 71 150'
18 RANCHO SANTA FE ROAD APPROX . 0.5 Ml. S/0 CADENCIA STREET 1.68 350'
19 EL CAMINO REAL APPROX . 0.5 Ml. N/0 FARADAY AVENUE 1. 64 100'
20 EL CAMINO REAL APPROX . 0.9 Ml . N/0 LA COSTA AVENUE 1. 55 1100'
21 ELM AVENUE APPROX . D .1 Ml. N/0 HIGHLAN D DRIVE 1. 54 75'
22 ALICANTE ROAD APPROX. D. 7 Ml. S/0 ALGA ROAD 1.50 600'
23 TAMARACK AVENUE APPROX . D. 4 Ml . S/0 ELM AVENUE 1. 48 300'
24 CARLSBAD BOULEVARD APPROX. 0 .1 Ml. S/0 WARM WATER JETTY 1.48 17 5'
25 MONROE STREET APPROX. 0. 5 Ml. S/0 MARRON ROAD 1. 45 22 5'
26 PASEO DEL NORTE APPROX . 0.2 Ml. N/0 CAMINO DE LAS ONDAS 1. 44 27 5'
27 PASEO DEL NORTE S/0 CAMINO DE LAS ONDAS 1. 41 425'
28 PALOMAR AIRPORT ROAD E/0 CARLSBAD BLVD . OVERPASS 1. 38 100'
29 PALOMAR AIRPORT ROAD E/0 RAILROAD OVERPASS 1. 27 125'
30 JEFFERSON STREET N/0 MARRON ROAD 1. 24 50'
31 PALOMAR AIRPORT ROAD W/0 RAILROAD OVERPASS 1. 23 367'
32 CARLSBAD BOULEVARD S/0 PONTO DRIVE SOUTH 1.18 650'
33 POINSETTIA LANE APPROX . 0.1 Ml. E/0 CARLSBAD BOULEVARD 1.15 50'
F IGURE 2
7
N.W.
CARLSBAD
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TABLE 1
LIST OF STREETS FIELD SURVEYED
FOR POTENTIAL GUARDRAIL INSTALLATION
PRIME ARTERIAL STREETS
1. El Camino Real
2. Melrose Drive
3. Olivenha in Road
4. Palomar Airport Road
5. Rancho Santa Fe Road
MAJOR ARTERIAL STREETS
1. Alga Road
2. Cannon Road
3. Carlsbad Boulevard
4. College Boulevard
5. La Costa Avenue -east of El Camino Real
6. Poinsettia Lane
SECONDARY ARTERIAL STREETS
1. Alicante Road
2. Avenida Encinas
3. Camino Vida Roble
4. El Fuerte Street
5. Elm Avenue
6. Faraday Avenue
7. La Costa Avenue -west of El Camino Real
8. Marron Road
9. Mision Estancia -(Calle de Fuente)
10. Monroe Street
11. Paseo Del Norte
12. Tamarack Avenue
12
APPENDIX
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1:1
1 1 /2:1
2:1
3:1
4:1
GUARDRAIL, MEDIAN BARRIERS, CRASH CUSHIONS Traffic Manual
0
Figure 7-1
EQUAL SEVERITY CURVE
( SEE TEXT FOR INSTRUCTIONS)
GUARDRAIL
LESS SEVERE
(PLACE GUARDRAIL UNDER THESE
___ ______. CONDITIONS ONLY WHEN THERE
IS A HIGH POTENTIAL FOR
RUNNING OFF THE ROAD.)
MOR E SEVERE
10 20 30
• EMBANKMENT HEIGHT -FEET
40 50
w a.. 0 .J en
.J
.J
LL
N ~
N .c
w a.. 0 .J en
I-::, u
_ 0_4 o-~--2 ..... O_--r-_4.,..:o=--~-s::..co=--_-..;;,0O,;;;__~___.-oo 0 20 40 60 80 100
-0.3
-0 .2
-0.1
0
0.1
0 .2
0.3
0 .4
0 .5
a: UJ
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a:~
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~~ o-
SHOULDER SLOPE
BREAK UNROUNDEO
::E.
UJ~~~.__--1--+-----+-----+----i a: ~
l5 ~ ... ,ci:
BARRIER NOT
WARRANTED
UJ -
d~---------+------+-------1------1
,c{ I
I--(I)= ~~ ~ ~~
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Traveled Way Obatacle
houlder
I
FILL SECTION
a: UJ
a: a: < CD
SHOULDER SLOPE
BREAK ROUNDED
BARRIER NOT
WARRANTED
-+-+--+---+----+-----t'--------IQ:Q
[ Clear one=
t-----t+--tt-----+ rr.■===,d;,C:::: 4
CUT SECTION z For curve
adju&tment
111 tut.
0 20
L..----'L..---'---'----'----'----'----'----'----'---' 2 : I
40 60 80 100 0 20 40
DISTANCE FROM EDGE OF TRAVELED WAY TO ROADSIDE
OBSTACLE ( FEET)
60 80
METRIC CONVERSION :
I mph= 1.61 Kmph
I ft :s 0.30!5m
Fig. 7-2 Clear Zone Width, Speed and Slope Criteria.
100-
w:J a.. er 0U
.J 0
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TABLE 7-2
Warrants for Nontraversable Hazards
Nontraversable Hazard Within Clear Traffic Barrier Required
Zone as Determined By
Yes 1 Figure 111-A-3 No
Rough rock cuts X
Large boulders X
Streams or permanent bodies of water
less than 2 ft. in depth X
Streams or permanent bodies of water
more than 2 ft. in depth X
Shoulder drop-off with slope steeper
than 1:1 and
a) Height greater than 2 ft. X
b) Height less than 2 ft. X
1All roadside obstacles within the clear zone should be removed
if possible, otherwise provide barrier protection.
Metri c Conversions
1 ft. = 0.3048 m
Warranls for Fixed Ohjcl'ls
Fixed Objects Within Clear Traffic Barrier Required
Zones as Determined t,y
FinttrP III-A-31 Yes No
Sign, traffic signal, and luminaire
supports2
a) Breakaway or yielding design
with linear impulse:3
1) less than 1,100 l b-sec X 2) greater than 1,100 lb-sec x4
b) Concrete base extending 6 in .
or more above ground X Fixed sign bridge supports X Bridge piers and abutmen ts at
underpasses X Retaining walls and culverts X Trees with diameter greater than 6 in. X'' Wood poles or ~osts with area greater
than 50 in . X''
1Fixed object should be removed or relocated so that a barrier is
unnecessary if practical.
2Breakaway or yielding design is desirable regardless of distance from traveled way. 3See discussion in text. 4A judgment decision (see discussion in text).
Metric Conversions:
1 lb-sec = 4.45 N-sec
1 in = 0. 02 54 m