20. Left turn traffic signal operation
CITY OF
CUPEIQINO
City Hall
10300 Torre Avenue
Cupertino, CA 95014-3255
(408) 777-3354
FAX: (408) 777-3333
PUBLIC WORKS DEPARTMENT
AGENDA ITEM
20
Summary
AGENDA DATE {'vvJfch. 101 2~ 1
,
SUBJECT
Discussion and Recommendation Regarding Protected-Permissive Left-Turn Traffic Signal
Operation.
BACKGROUND
Protective-permissive (PIP) signal operation was first implemented in Cupertino in 1992.
PIP operation means that during one portion of a traffic signal cycle, vehicles turning left
from the main street onto the side street must yield the right-of-way to oncoming vehicles
(permissive portion), while during another portion of the cycle the vehicles turning left
have the right-of-way and oncoming vehicles have a red light indication (protected
portion).
In Cupertino, this is achieved by displaying a flashing red left arrow to left-turning
vehicles during the permissive portion, and a (non-flashing) green arrow during the
protected portion. There are currently four intersections within Cupertino which use PIP
phasing. These are Stevens Creek Blvd/Saich Way, Stevens Creek Blvd/Torre Ave,
Stevens Creek Blvd/Portal Ave, and Pruneridge AveIHP driveway (although PIP phasing
has been turned off at this intersection for some time).
DISCUSSION
PIP signal operation has been in use in various locations throughout the United States since
the 1960's, although there is much variability of the signal display indicating the
permissive phase among various jurisdictions. The Manual Of Uniform Traffic Control
Devices (MUTCD) standard is a circular green indication; other variations in current use
include the flashing circular yellow, flashing yellow arrow, flashing circular red, and
flashing red arrow (such as in Cupertino).
Although a circular green indication for the permissive portion is the MUTeD standard, a
flashing red arrow was chosen for Cupertino so that when the traffic signal changes from
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Printed on Recycled Paper
protective left turn (steady green arrow) to the permissive left turn (flashing red arrow),
after the steady yellow arrow clearance interval, there is a distinct change in the color
(green to red), mode of operation (steady to flashing), and location (bottom of signal head,
to third from bottom). These changes are intended to alert motorists that there is a change
in the left turn signal operation that requires their immediate attention.
In the time since PIP signal operation was first implemented in Cupertino, there has been a
significant amount of outside research done on the topic. In aggregate, the research
suggests that when PIP signal operation is used, vehicle delay decreases, fuel usage
decreases, vehicle progression is improved, and vehicle crashes increase. With respect to
crashes, current crash reporting techniques do not adequately document causes of a crash
as they relate to traffic signal operation, much less the particular signal display, so a direct
study of crash statistics to determine the relative "safety" of a particular type of traffic
signal phasing (such as PIP) is difficult.
Staff reviewed crash statistics at the three Cupertino intersections currently operating PIP
signal phasing and found that at the three intersections where accidents occurred,
approximately 38% of the accidents were left turn or V-turn related.
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1/2004 - 8/2006
LOCATION
Portal/Stevens Creek
Stevens Creek/Torre
HPIPrunerid e
Stevens Creek/Saich
Total
Accidents
The records are not entirely clear in all cases whether or not these accidents occurred
during the permissive (flashing red) phase, although it appears that most, if not all, did.
However, the reports are also not clear on whether all 38% of the accidents were
necessarily the result of the existing PIP operation.
Cupertino Experience
The acceptance of PIP signal operation in the Cupertino community has been mixed. The
flashing red arrow used in Cupertino to denote the permissive portion is quite unique-to
staff's knowledge, only one other municipality in the country (Dover, Delaware) uses the
flashing red arrow in PIP signal operation. This has resulted in some driver confusion, and
the need to supplement the intersections with additional signing and striping, such as the
diagonally striped "stop box" within the left turn pocket and the "Stop Then Yield On
Flashing Red Arrow" signs, in order to clarify what the correct driver behavior should be.
One of the primary principles to be adhered to in the design of traffic control devices, as
stated in the MVTCD, is to "convey a clear, simple meaning"; violation of this rule can
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generally result in non-compliance of the traffic control device, a degradation of safety, or
both. This, of course requires knowledgeable and careful driving habits, which some
drivers do not possess or they simply ignore.
Perhaps the most comprehensive study on PIP signal operation is the National Cooperative
Highway Research Program (NCHRP) Report 493, "Evaluation of Traffic Signal Displays
for Protected/Permissive Left- Turn Control", completed in 2003. Among the
recommendations contained within the report are that flashing red arrows not be used for
typical PIP signal operation, because the "stop then proceed when a gap is available"
message is not consistent with the way a typical PIP intersection typically operates, and
because a flashing permissive red indication may dilute the meaning of other red stop
indications.
ALTERNATIVES AND OPTIONS
Should Council wish to eliminate the confusion associated with the PIP signal operation
and enhance safety, it is recommended that the flashing red permissive portion of the
signal phasing be eliminated and that the intersections be converted to standard protected
left-turn phasing (solid green arrow for left-turning vehicles).
It should be noted that, while removing the PIP phasing from Cupertino's intersections
may enhance safety, this could result in some minor degradation in the Level of Service
(LOS) of the intersections. This is due to the fact that, while currently some left-turning
traffic can be accommodated through gaps in the flow of opposite direction traffic during
the permissive phase, all left-turning traffic would occur only through a protected phase
with opposite direction traffic stopped (red light).
Consequently a greater percentage of the signal cycle would need to be allocated for left-
turning vehicles, robbing time from the other movements. This impact could potentially be
mitigated somewhat through modification of the existing signal coordination plans,
implementation of conditional service (allowing a protected left-turn movement more than
once in a given cycle), or a combination of both.
To summarize, the pros and cons of eliminating the flashing red arrow (permissive) phase
of the signals are as follows:
PROS
Removes non-standard si al 0 eration
Enhances safet
Eliminates driver confusion
CONS
Increases vehicle dela s
Minor De adation of Level of Service
COMMUNITY NOTIFICATION
This item has been widely noticed, including an article in The Scene and posting on the
City's web site.
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FISCAL IMPACT
The cost of eliminating the PIP signal operation at four intersections in Cupertino is
approximately $60,000. This cost, which is currently programmed in the 2006-07 CIP
Fund 420-9556, primarily involves removing and replacing signal head standards and
minor signing and striping modifications. Not included in this estimate is the indirect cost
of staff time necessary to design, implement and test new signal timing plans at each
intersection.
ST AFF RECOMMENDATION
Staff recommends that the PIP signal phasing be removed from Cupertino intersections,
and replaced with protected-only (solid green arrow) left-turn signal phasing.
Submitted by:
Approved for submission:
~~al~uaUd
Director of Public Works
~
David W. Knapp
City Manager
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Grace Schmidt
From:
Sent:
To:
Subject:
Vicki Guapo
Thursday, March 22, 2007 2:53 PM
City Clerk
FW: Agenda Item #20, 3/20/07 City Council Meeting
FYI, this just arrived.
vic
-----Original Message-----
From: Tien and Stoeckenius [mailto:kiwi@orimp.com]
Sent: Monday, March 19, 2007 2:45 PM
To: Kris Wang; Patrick Kwok; Richard Lowenthal; Dolly Sandoval; Orrin
Mahoney; City of Cupertino Public Works - Engineering Div; City of
Cupertino Traffic Department
Subject: Agenda Item #20, 3/20/07 City Council Meeting
To: Cupertino City Council, Cupertino Public Works Department
Subj: City Council Meeting Agenda Item #20
Protected-permissive Left-turn Traffic Signal Operation
We are sending this email as we will not be able to attend tomorrow's
City Council meeting due to other commitments.
We support the recommendation of the Public Works Department to
eliminate the protected/permissive (flashing red) left turn signal at
the intersections on Stevens Creek Blvd. Our support is based
on three considerations:
1. Protected/permissive signaling is useful for a range for traffic
volumes between those appropriate for purely permissive signaling
and fully protected signaling. However, traffic volumes on
Stevens Creek Blvd. are now heavy enough that the benefits of
protected/permissive signaling over fully protected signaling
are lost, and the risks associated with the permissive phase
greatly increased.
2. particularly at the corner of Saich Way and Stevens Creek Blvd.,
the left turn signal is used primarily for U-turns (from eastbound
to westbound on Stevens Creek Blvd.). This motion typically
conflicts with right-turn movements from southbound Saich Way to
westbound Stevens Creek Blvd. This is a hazardous situation as
each vehicle is outside of the normal field of view of the other,
and outside the direction that requires the most driver attention
(both drivers are looking primarily at oncoming westbound traffic on
Stevens Creek Blvd.).
Given the volume of traffic on Stevens Creek Blvd. in this area,
both drivers may hasten their turn to fit into an available gap in
traffic. We know of at least one accident with significant
physical damage that arose in this manner.
3. The particular signal pattern used in Cupertino involves a
confusing and potentially hazardous transition from the permissive
phase (flashing red arrow) to the non-permissive phase (solid red
arrow) .
There is no intermediate stage to warn of the forthcoming change
from the permissive signal to the non-permissive phase, nor is it
easy to introduce one, given the choice to use a flashing red arrow
1
to indicate the permissive turn period.
We hope that the Council will act on this issue as soon as possible as
we feel that continued operation of the protected-permissive left-turn
traffic signal is more of a detriment to safe traffic flow than an
asset.
Thank you.
Julia Tien and (Mr.) Jan Stoeckenius
22386 Cupertino Road
tel: 408 996 7467 (office), 408 996 2064 (home)
email: kiwi@orimp.com
2
Cas~. Details
Ct
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Case Number:
Status: Resolved
Location of Request: Cupertino CA
95014-3255
Corner of
Portal and
Stevens Creek
Boulevard
(maP)
Customer:
16968
Pochylski, Tom
external customer
19975 Price AVE
Cupertino CA 95014 (map)
(408) 255-7575
tom 1 pochylski@netzero.net
~~
Preferred Contact Method: Email
Submitted By: Pochylski, Tom
customer
Request Type: Suggestion
Primary Owner: Guapo, Vicki
Topic: Traffic>Signals, Signs &
Markings
Date/Time Created: 03/12/2007
11:39
Date/Time Closed: 03/12/2007
12:35
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i Original Request
I apologize in advance if this is NOT the proper forum to use to communicate my
. opinion regarding the PIP signals in Cupertino. However, I will be out of town on
3/20 (the next City Council meeting) and won't be able to provide any testimony
during that particular meeting.
I live on Price Avenue and use the PIP signal at Portal and Stevens Creek Blvd quite
often. My only objection to this system is that, even after stopping the main flow of
traffic (on SCB, that is) and giving cross traffic a chance to go (north and south on
, Portal), the same signal does not give left turning traffic an arrow to proceed prior to
giving the "green" to the stopped SCB traffic. If you are going to interrupt this main
flow of traffic anyway, it would be nice if you could continue this interruption just a
bit longer to accomodate any left turning traffic onto NB or SB Portal. I guess this is
much more important during rush hour when opportunities to turn left are few and
far between. Hopefully, I expressed myself adequately to be understood...
, thanks in advance for listening!
- Tom Pochylski
Customer Communications
Date
From
Text
03/12/2007 Guapo, Details>> Good afternoon Tom: Thank you for your comments
12:35 Vicki on protective/permissive (P/P) traffic signal operation in
general and for Portal Ave./Stevens Creek Blvd. I will forward
your comments to the City Clerks office. As for the protected
left turn operation east west directions at Portal Ave./Stevens
Creek Blvd., if the PIP operation is removed, the traditional
protected left turn operation will return. That is, without getting
too technical, the vehicle movement sequence has a certain
order and if vehicles are present on all approaches of the
intersection, left turns will be serviced first. Certainly, the traffic
signal timing for the left turns may be adjusted now, later if the
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removal of PIP operation goes in effect. I hope this is helpful
and if you have any questions, please call me. Vicki Guapo
Senior Traffic Technician City of Cupertino 408.777.3243
Internal Activity
Internal Notes
I No records for internal activities found
Tasks
Complete Due Subject Assigned By Assigned To Status
Case Contacts
Role
Name
Email
Phone
Primary Owner
Secondary Owner
Guapo, Vicki
Stillman, David
Vickig@cupertino.org
davids@cupertino.org
Attachments
No attachments found
Activity History
Date
Event
Description
03/12/2007 12:35 Change Status status change during send email