HomeMy WebLinkAboutNB 4 LEFT TURN PHASING 02-05-90DATE:
TO:
FROM:
SUBJECT:
JANUARY 31, 1990
WILLIAM HUSTON, CITY MANAGER
PUBLIC WORKS DEPARTMENT/ENGINEERING DIVISION
LEFT TURN PHASING ON WALNUT AT BROWNING
RECOMMENDATION:
NEW BUSINESS N0. 4
2-5-90
Inter - Com
It is recommended that the City Council approve the modification of the
Walnut/Browning traffic signal and direct staff to include this project in the
1990-91 Capital Improvement Budget. The modification would involve the
installation of eastbound Walnut Avenue left turn phasing.
BACKGROUND:
At the City Council meeting of January 2, 1990, staff was requested to evaluate
the need for an exclusive eastbound Walnut Avenue left turn phase at the
subject intersection.
DISCUSSION:
Protected or "exclusive" left turn phases should be considered where other less
restrictive measures are available such as:
1. A complete prohibition of left turns (assuming that other and more
convenient replacement routes are available)
2. A geometric change to the intersection which would not involve
significant affects elsewhere in the vicinity of the intersection.
If such measures are not feasible (as is true in this case), then a
modification to the existing signal -involving the installation of new signal
heads, new left turn green arrow signal heads, and changes to the signals'
controller are appropriate if one or more of the following conditions exist.
These conditions include higher levels of left turn accidents, to excessive
delay to left turn vehicles, or a peak hour arithmetic product (involving left
turns and opposing through movements) that exceeds the value of 100,000. The
last element involving the figure of 100,000 is a limiting value which from
experience, generally conforms to a point where left turn safety could be
compromised if the exclusive left turn signal phase were not available.
Left Turn Phasing
page 2
For the Walnut/Browning intersection, there is neither an accident problem nor
a case where excessive left turn delay exists. However, during the afternoon
peak hour (between 5:00 and 6:00 p.m.), the arithmetic product between
eastbound left turns and opposing westbound through movements is well over
100,000. Therefore, although the accident and vehicular delay situation at the
intersection is good, exclusive eastbound left turn phasing should nevertheless
be installed because of the volume of left turn and opposing through movements.
Such a measure would help to maintain the good accident history of the
intersection.
The estimated cost for exclusive left turn phasing for eastbound Walnut Avenue
traffic to northbound Browning Avenue is $40,000. This work would include a
new signal standard, traffic signal heads, loop detection and modification to
the traffic signal controller. It is suggested that this modification be
scheduled and included within the 1990-91 Capital Improvement Budget.
Bob Ledendecker
Director Public Works/City Engineer
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