TC - Item 3B - Proposed Traffic Signal Improvements at Walnut Grove Avenue/ San Gabriel Blvd. Route 60 IntersectionsTO: TRAFFIC COMMISSION
FROM: CHRIS MARCARELLO, PUBLIC WORKS DIRECTOR
DATE: SEPTEMBER 22, 2011
SUBJECT: PROPOSED TRAFFIC SIGNAL OPERATIONAL IMPROVEMENTS AT SAN
GABRIEL BOULEVARD /SR -60 WESTBOUND RAMPS AND SAN GABRIEL
BOULEVARD/WALNUT GROVE AVENUE
SUMMARY
Traffic operational conditions have worsened in recent years at the intersections of San
Gabriel Boulevard /SR -60 Westbound Ramps and Walnut Grove Avenue. Motorists
traveling through these two heavily congested signalized intersections experience delay,
congestions, and conflicts on a daily basis, apparently due to inadequate distribution of
green time and inefficient phasing of the traffic signal cycles, particularly during commuter
peak hours. Staff is working on appropriate traffic improvement measures to be
implemented at these intersections to mitigate the problems and is requesting input and
support from the Traffic Commission.
Staff Recommendation
It is recommended that the Traffic Commission:
1. Provide input on proposed traffic improvement measures developed based on in-
depth investigation at these intersections;
2. Recommend to the City Council that improvements be made at these intersections.
ANALYSIS
In August 2011, staff undertook an investigation into the traffic operational problems
experienced by the commuter traffic at the two intersections of San Gabriel Boulevard — at
SR -60 freeway westbound ramps and at Walnut Grove Avenue. A weekday peak period
traffic count of turning movements was conducted at each intersection for the morning and
afternoon peak periods. These counts, along with existing intersection lane configuration
and signal phasing information, were analyzed using traffic engineering /analysis software
to determine existing intersection performance, traffic operational problems, and to develop
potential improvement measures to mitigate these problems.
The traffic engineering investigation and analysis conducted at the two intersections
Traffic Commission Meeting
September 22, 2011
Page 2 of 3
resulted in identifying traffic problems that could be addressed by modifying existing signal
operations and by restricting certain permitted movements at these intersections during
traffic signal phases. These improvements, once implemented, are expected to significantly
reduce undue delays as well as the potential for accidents.
Although the measures would increase the number of signal phases at the intersections
resulting in slight increase in delay, they would significantly improve traffic safety by
eliminating potentials for conflicts between opposing traffic, while maintaining intersection
levels of service (LOS) at a level acceptable for urban area intersections.
The proposed improvement measures are described in the following
San Gabriel Boulevard at Walnut Grove Avenue
Prohibit northbound right turns (from northbound San Gabriel Boulevard to
eastbound Walnut Grove Avenue) during the eastbound split phases.
• Provide split phases for the eastbound (driveway) and westbound (Walnut Grove
Avenue) movements; by reconfiguring signal phasing so that an exclusive phase is
provided only for eastbound (left -turn, right -turn and through) movements, and
another exclusive phase is provided only for westbound (left -turn, right -turn and
through) movements. Currently, all eastbound movements are allowed during the
permitted single phase for westbound movements, creating confusion, delay and
potential for conflicts), and
The City controls all signal operations at this intersection. However, there will be some
coordination with the adjacent San Gabriel /SR -60 intersection since it is close in vicinity.
San Gabriel Boulevard at SR -60 Freeway Westbound Ramps
• Provide split phases for the eastbound and westbound movements; by reconfiguring
signal phasing so that an exclusive phase is provided only for eastbound (left -turn,
right -turn and through) movements, and another exclusive phase for westbound
(left -turn, right -turn and through) movements. Currently, all eastbound and
westbound movements are allowed during one single phase, creating confusion,
delay and potential for conflicts), and
• Prohibit westbound right turns (from off -ramp to northbound San Gabriel Boulevard)
during the eastbound split phases.
Due to the shared operation of this intersection with Caltrans, these signal modifications will
need to be shared, analyzed, and approved by Caltrans officials. Due to these coordination
issues, it is thought that these proposed improvements will take a longer time period to
implement.
Traffic Commission Meeting
September 22, 2011
Page 3 of 3
Public Notice
This agenda item has been noticed through the regular agenda notification process.
Submitted by:
CHRIS MARCARELLO
Public Works Director
Attachments:
1. Overhead Map
2. Intersection Traffic Counts
3. Detailed Analysis
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Intersection Performance and Safety Analysis
San Gabriel Boulevard at SR -60 Westbound Ramps and Walnut Grove
Avenue, City of Rosemead, California
A field investigation was conducted and traffic counts (of AM and PM peak period turn
movements) were taken during the third week of August, 2011 at the intersection of San Gabriel
Boulevard and SR -60 Westbound Ramps and at San Gabriel Boulevard and Walnut Grove
Avenue in the City of Rosemead. This report presents the results of this investigation as well as
an analysis of the intersection performance and traffic safety conditions. Traffic engineering
recommendations for improvements were also provided.
The summary of intersection traffic counts conducted during the AM peak period (7:00 AM to
9:00 AM) and the PM peak period (4:00 PM to 6:00 PM) on Thursday, August 18, 2011 (a
typical weekday) are attached to this report. Based on these counts, it has been determined that
both of these intersections show an AM peak hour between 7:45 AM and 8:45 AM, and a PM
peak hour between 5:00 PM and 6:00 PM.
An accident history analysis for the last three years (2008 through 2010) shows that there have
been a total of 15 accidents reported at or near Walnut Grove Avenue /San Gabriel Boulevard,
and 1 accident reported at San Gabriel Avenue /SR -60 Freeway (see the attached accident
history). At least 3 of these accidents are directly related to the signal conditions and others are
likely to be related to intersection configurations and /or speeding.
San Gabriel Boulevard is posted with a speed limit sign of 45 miles per hour.
The intersections were analyzed using Synchro traffic analysis software to determine existing
level of service (LOS) and intersection delays under existing signal cycle and phasing for various
movements. Base on an observation of traffic safety conditions, it has been determined that
providing separate phases for eastbound and westbound movements (i.e., splitting the phases)
will improve traffic safety. The splitting of phases will result in movement of eastbound traffic
during an exclusive phase (when all other traffic will remain stopped). The same will apply when
westbound traffic will move during an exclusive phase. The results of intersection level of
service with existing and proposed signal phasing are presented in the table below. The details of
Synchro calculations are also attached.
Intersection
Peak Hour
Existing Condition
Proposed* Conditions
Delay, Sec. LOS
Delay, Sec. LOS
San Gabriel Boulevard @
SR -60 Westbound Ramps
AM
6.7
A
9.5
A
PM
9.1
A
15.9
B
San Gabriel Boulevard @
Walnut Grove Avenue
AM
7.8
A
9.4
A
PM
12.0
B
13.6
B
* Proposed Conditions include splitting of signal phases for eastbound and westbound
movements at both intersections.
San Gabriel Boulevard Intersection Analysis
Page 2 of 4
The results show that both intersections are currently operating at an acceptable LOS A or B (i.e.
LOS better than D). With proposed split phasing the delay at intersections will slightly increase,
but the LOS will not deteriorate to a level worse than LOS B. Therefore split phasing for
eastbound and westbound traffic at both intersections are recommended. It is also to be noted
that during eastbound split phase, westbound right turn at SR -60 intersection as well as
northbound right -turn at Walnut Grove Avenue should be prohibited. This will reduce driver's
confusion, delays and potential for conflicts currently being created due to lane configurations
and single phasing of eastbound and westbound movements Because current traffic volumes for
eastbound movements at both intersections are very low, the extra time needed for this traffic in
the signal cycle will not have any significant impact on the overall signal performance at these
intersections.
Recommendations:
1. At the intersection of San Gabriel Boulevard and SR -60 Westbound Ramps,
provide split phases for the eastbound and westbound movements; i.e.,
reconfigure signal phasing so that an exclusive phase is provided only for
eastbound (left -turn, right -turn and through) movements, and another exclusive
phase is provided only for westbound (left-turn, right -turn and through)
movements. Currently, all eastbound and westbound movements are allowed
during one single phase, creating confusion, delay and potential for conflicts.
Also, prohibit westbound right turns during the eastbound split phase.
2. At the intersection of San Gabriel Boulevard and Walnut Grove Avenue, provide
split phases for the eastbound and westbound movements; i.e., reconfigure signal
phasing so that an exclusive phase is provided only for eastbound (left -tam, right -
turn and through) movements, and another exclusive phase is provided only for
westbound (left -turn, right-turn and through) movements. Currently, all
eastbound and westbound movements are allowed during one single phase,
creating confusion, delay and potential for conflicts. Also, prohibit northbound
right -turns during eastbound split phase.
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