ITE Journal – December 2019 - 38

The use of flashing yellow arrows is becoming more prevalent
in common practice in the United States because of the operational
benefits. Even though flashing yellow arrows are considered as
equally understood as a green ball, it is generally accepted that
flashing yellows can be safer than the traditional yield-on-green
indications, which can reduce crashes up to 24 percent.2,3
Traditionally, most government agencies don't allow for the
use of protected/permitted operation at signalized dual left turn
lanes, because of the safety implications. With more government
agencies using flashing yellow arrows, there are changes in
policies to allow for protected/permitted operations for dual left
turn left turn movements, but is rarely implemented. There are
some government agencies developing guidelines or criteria for
the time of day use of the flashing yellow arrow by predicting
the risk of left turn crash occurrences throughout the day.4 Some
government agencies will procure an advanced traffic signal
control technology through the Federal Highway Administration systems engineering analysis.5 However, these technologies
are expensive due to high infrastructure cost and procurement
of the technology.

Adding Flashing Yellow Arrows to Mainline Dual Left Turns
For this study, the Wisconsin Department of Transportation
(WisDOT) arranged to have the traffic signal faces for the
northbound and southbound left turn directions retrofitted from
a 3-section protected only operation to a 4-section flashing yellow
arrow operation at State Trunk Highway (STH) 67 and County
Highway (CTH) B (Valley Road), in which both left turns have dual
left turn lanes. Figure 1 shows the WisDOT traffic signal plan for
STH 67 and CTH B (Valley Road). The intersection was chosen
because of the following characteristics:
 Intersection geometric reconstruction to modern safety
standards (including neutral left turn offset);
 Traffic signal reconstruction (updating to a safer head per lane
configuration);
 Minimal horizontal curvature;
 Minimal signal infrastructure revision cost, which include
(other than controller programming):
 New brackets and signal faces (both procurement and
in-field modifications); and
 Signal video detection (in-field modifications only).

Figure 1. WisDOT Traffic signal plan for STH 67 and CTH B (Valley Road).
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ITE Journal – December 2019

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