HomeMy WebLinkAbout1987-05-04; Traffic Safety Commission; ; Request for roadside guardrail be installed on the west side of RSF and La Costa Avenue and Cadencia StreetCITY OF CARLSBAD
TRAFFIC SAFETY COMMISSION
COMMISSION REPORT OF: May 4, 1987 ITEM NO. 6B
LOCATION: Rancho Santa Fe Road -La Costa Avenue to
Cadencia Street
INITIATED BY : Alan Reece, 7442 Trigo Lane, Carlsbad, CA 92009
BACKGROUND:
DATA:
Mr. Reece is requesting that a roadside barrier (guardrai l)
be i nstalled on the west side of Rancho Santa Fe Road
between La Costa Avenue and Cadencia Street at locations
where the ground slopes from the roadway towards the
back yards of homes along Rancho Santa Fe Road. He is
proposing approximately 2,000 feet of guardrail.
Rancho Santa Fe Road, between La Costa Avenue and
Cadencia Street is a two ( 2) lane asphal tic-concrete
roadway having a two-way volume of 15,000 cars per day.
Homes on the west side of Rancho Santa Fe Road were
constructed at an elevation lower than the roadway. As
a result, there is a slope that begins approximately ten
(10) f eet from the west edge of the roadway that slopes
down t o the backyards of the homes. This slope varies
in height from several feet to a height of approximately
50 f eet .
When guardrail is necessary, it is installed to reduce
the severity of the "run off the roadway" type of
accidents. This is accomplished by dissipating the
energy of the errant vehicle and deflecting the vehicle
away from an embankment or a fixed object.
Not all roadside conditions require a guardrail. To
reduce accident severity, guardrail should only be
installed where striking the guardrail is less severe
than going down an embankment or striking a fixed
object. It should be installed only where it has been
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TRAFFIC SAFETY COMMISSION
COMMISSION REPORT OF: May 4, 1987
(Continued)
ITEM NO. 6B
determined that safety will be improved by the installation
and should not be used solely as a barricade.
Primary contributors to embankment accident severity is
the height and slope of the embankment. In the CALTRANS
Traffic Manual, an Equal Severity Curve is provided
(attached). This curve compares the accident severity
of h itting a guardrail with the severity of going off an
embankment. The heavy line indicated on the Equal
Severity Curve represents combinations of embankment
height and slope that results in accident severities
generally equal to average guardrail accident severity.
Overall , acci dent severity will generally be less if
guardrail is used on embankments that plot above the line.
CALTRAN S provides a procedure to be followed when
guardrail is being considered at a given location, as
follows :
1. Gu ardrail should be installed only at locations of
high run-off-the-road accident history or potential
for such accidents. Evaluation of the potential
frequency of accidents at a given location is based
on the following general considerations:
a. Alignment -Isolated curves on otherwise high
standard roads increase the probability of
running off the road. Also, on roads with
curving alignment, curves that are sharper
than those generally used, compound curves, or
curves with larger central angles have a
greater probability of run-off-the-road
accidents. The outside of curves of less than
about 1,000-foot radius, and especially those
on downhill gradients in excess of two percent
(2%) should be given special consideration.
b. Volume of Traffic -The higher the volume of
traffic, the greater is the probability of
"run-off-road" accidents occurring.
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TRAFFIC SAFETY COMMISSION
COMMISSION REPORT OF: May 4, 1987
(Continued)
ITEM NO. 6B
c. Roadside Recovery Area -The narrower the
recovery area, the greater the probability
that a "run-off-road" vehicle will go down an
embankment.
d. Climatic Conditions -Frequent dense fog or
snow and ice conditions increase the probability
of running down an embankment. In addition,
locations subject to high velocity cross winds
have an increased probability of vehicles
running off the road.
2. Us ing Figure 7-1, determine whether hitting guardrail
or going off the embankment may be more severe.
Place guardrail only when the embankment is more
severe and there has been a history of accidents or
there is potential for accidents considering the
preceeding factors.
Staff h as recently received many requests for guardrail
in various parts of the City. Due to the potential
accident severity and the high cost of installing guard-
rail , approximately $35.00 per lineal foot, it is
important that guardrail not be installed indiscriminately.
Other costs associated with guardrail are maintenance
and accident costs. Every ef fart should be made to
eliminate hazardous conditions by upgrading a roadway
that requires the need for a roadside barrier.
In order to determine locations that require guardrail,
an inventory of roads needs to take place to identify
such l ocations. Once identified, each location can be
ranked in the order of need and placed on a priority
list. This list would then be used in the annual CIP
review process to budget money for the needed guardrail
installation. Circulation Element streets and any other
high a ccident locations would be inventoried first and
the guardrail priority list established therefrom. Once
the list is compiled, it would be brought back to the
Traffic Safety Commission for review.
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TRAFFIC SAFETY COMMISSION
COMMISSION REPORT OF: May 4, 1987
(Continued)
RECOMMENDATION:
ITEM NO. 6B
The Traffic Safety Coordinating Committee recommends
that a Guardrail Priority List of circulation Element
roads a nd other high accident locations be compiled for
review by the Traffic Safety Commission and used for
future CIP budget purposes.
NECESSARY CITY COUNCIL ACTION:
No City Council action required at this time. Once the
list is approved by the Traffic Safety Commission, it
would be taken to City Council for revi ew and comment.
6
CADENCIA STREET
POWER LINE
REQUESTED
GUARD RAIL
LA COSTA AVENUE
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GUARDRAIL, MEDIAN BARRIERS, CRASH CUSHIONS Traffic Manual
0
Figure 7-1
EQUAL SEVERITY CURVE
(SEE TEXT FOR INSTRUCTIONS)
GUARDRAIL
LESS SE VERE
(PLACE GUARDRAIL UNDER THESE
---~ CONDI TIONS ONLY WHEN THERE
IS A HIGH POTENTIAL FOR
RUNNING OFF THE ROAD.)
MOR E SEVERE
10 20 30 40
EMBANKMENT HEIGHT -FEET
50
(