| Flashing Yellow Arrows
last updated June 29, 2019
Over the past
years, the implementation of the flashing yellow arrow (FYA) traffic
signal has become widespread. While the meaning of the signal
generally well-understood ("yield to turn left"), the reason for its
replacement of previous "permissive left" signals is not widely
understood with some cynics asserting it to be a waste of money. This
page is intended to explain the reason why the signal was developed and
why it is superior to previous permissive left signals.
(A "permissive left" is
when a signal permits you to turn left but the turn is not protected.)
The "Yellow Trap"
fully understand the reason for the FYA, you have to first understand a
traffic situation known as the "Yellow Trap". This occurs
driver enters an intersection on a green circular signal to wait for
a gap in oncoming traffic before turning left. While waiting, their
signal turns yellow. Believing that oncoming traffic also has
yellow and therefore expecting oncoming traffic will slow down
and stop, the
driver turns left only to be T-boned by an oncoming vehicle.
Why did this happen? Because
driver did not realize that oncoming traffic still had a green light
and that his signal was turning red to allow for a protected left for
a driver will
realize that oncoming traffic does still have a green and
so they will then continue to wait in the intersection while their
is red and their blood pressure increases, or they will try to back out
of the intersection, both of which are undesirable outcomes.
of these dangers, traffic engineers for years had been trying a variety
solutions for the Yellow Trap. The most basic was signage
those below indicating that oncoming traffic had an extended green. While a cheap and easy fix, many drivers did not understand
the signs meant (or just didn't read the sign to begin with) and still
ended-up in the Yellow Trap situation.
engineers in Dallas came up with what is regarded as the first
signalized solution. With conventional permissive left turns,
left turn signal shows the same circular signal as the adjacent through
other words, when northbound through traffic has a green or
the northbound left turn also shows the same green or red circular
Dallas solution was to de-couple the left turn permissive signal from
the adjacent through signal and instead sync it with the
through signal. That way, when the northbound left turn signal
turning red, the southbound through signal was also turning red at the
same time, thus allowing a northbound motorist waiting to turn left to
complete his turn safely. This became known as "Dallas
Watch the animated comparison of left turn signals in the first
site under "Other sites of interest" at the bottom of this page.)
side benefit of Dallas phasing was that there was increased time each
cycle for left turns, which helped move more vehicles through
accommodate this change using existing signal displays, engineers had to
install louvers in the green circular signal for the left turn so that
the adjacent through traffic could not see it and perhaps get confused. These
louvers worked, but reduced the visibility of the green signal
markedly (especially if the signal got out of alignment), so it was
less than ideal.
problem, though, was that some drivers became confused when
seeing red signals for the adjacent through traffic but a
green signal for the left turn lane. Because drivers
are accustomed to
this when they have a protected left, many drivers-- either
to instinct and/or not paying close attention--
started turning before recognizing that the green signal was not an
arrow and that they in fact were supposed to yield. The
results of this were often disasterous.
Typical signal display for
conventional permissive left turn.
understand to yield when turning left in this situation.
Typical signal display for
permissive left turn in "Dallas phasing" during
oncoming protected left phase. Drivers sometimes misinterpreted
to indicate a protected left turn.
FYA to the rescue
solve the problems of the Dallas display, federal traffic safety
officials began a study in the mid '90s to evaluate and select a better
signal solution. Various options were considered including
various combinations of different colored flashing arrows and circular
signals (e.g. flashing red arrow, flashing red circle, flashing green
arrow, etc.) The FYA, widely used in Europe for some time,
was included in the evaluation.
driver comprehension studies, the FYA was found to
have the best inherent understanding of the solutions
studied. Furthermore, drivers
who did not understand its meaning tended to interpret it to
mean "wait", (i.e. a "safe failure") whereas with the green
drivers who misunderstood it usually interpreted it as a protected turn
(i.e. a "critical
failure".) The FYA also proved to be more versatile
in terms of
signal displays and operation than the other displays studied.
on the results of the studies, the FYA was field tested beginning in
2006 in localities in Maryland, Oregon, Florida, and Arizona. Those tests confirmed that the FYA solved the Yellow Trap and
so with a generally-understood signal that,
when misinterpreted, typically resulted in a safer default
outcome. As a
result, the signal was approved
for general use in the 2009 Manual on Uniform Traffic Control Devices
and Dallas displays were prohibited for new installations.
Why the FYA is easily understood
FYA is instinctively understood by most drivers because of its
confomity with other flashing yellow indicators. With traffic
signals, a flashing yellow light means "proceed with caution", so a
flashing yellow arrow inherently conveys the meaning "turn left with
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