| Flashing Yellow Arrows |
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| This page
last updated June 3, 2023 |
 Over the past
few
years, the implementation of the flashing yellow arrow (FYA) traffic
signal has become widespread. While the meaning of the signal
is
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 an intentional 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"
To
fully understand the reason for the FYA, you have to first understand a
traffic situation known as the "Yellow Trap." This occurs
when a
driver enters an intersection on a green circular signal to wait for
a gap in oncoming traffic before turning left (which, by the way, is
perfectly legal and a common practice in many places.) While waiting,
their
signal turns yellow. Wanting to get out of the intersection before the
signal changes to red, and believing that oncoming traffic also has
a
yellow and therefore expecting oncoming traffic will slow down
and stop, the
driver turns left only to be T-boned by an oncoming vehicle because the
oncoming traffic actually still had a green signal.
Sometimes
in this situation,
a driver will instead smartly opt to wait for oncoming traffic to actually stop,
or may somehow know
that oncoming traffic does still have a green, and
so they will then continue to wait in the intersection while their
light turns red. However, sitting in an intersection with a red light
often leads the driver to quickly become anxious, making them prone to
take
more risky turns, or they will try to back out
of the intersection, both of which are undesirable outcomes.
Previous solutions
Because
of these dangers, traffic engineers for years had been trying a variety
of
solutions for the Yellow Trap. The most basic was signage
like
those below indicating that oncoming traffic had an extended green.
While a cheap and easy fix, many drivers did not understand
what
the signs meant (or just didn't read the sign to begin with) and still
ended-up in the Yellow Trap situation.
Traffic
engineers in Dallas came up with what is regarded as the first
signalized solution. With conventional permissive left turns,
the
left turn signal shows the same circular signal as the adjacent through
signals (see first example below.) In
other words, when northbound through traffic has a green or
red,
the northbound left turn also shows the same green or red circular
signal. The
Dallas solution was to de-couple the left turn permissive signal from
the adjacent through signal and instead sync it with the
opposing
through signal. That way, when the northbound
left turn signal
was
turning red, the southbound
through signal was also turning red at the
same time, thus meeting the northbound left turning
motorist's expectation that opposing traffic will stop and thus
allowing them
complete their turn safely. This became known as "Dallas Phasing".
(Confused?
Watch the animated comparison of left turn signals in the
first
site under "Other sites of interest" at the bottom of this page.)
A
side benefit of Dallas phasing was that there was increased time for left turns, which helped move more vehicles
through
the
intersection each cycle, thus helping to ease congestion.
To
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 would not see it and perhaps get confused.
These
louvers worked reasonably well for that purpose, but also reduced the visibility of the
green signal
markedly, especially if the signal got out of alignment or was on a
span wire and being blown by the wind. So it was less than ideal.
Another
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
usually seeing
this when they have a protected left, many drivers-- either
due
to instinct and/or not paying close attention--
started turning before recognizing that the green signal was not
actually an
arrow and that they in fact were supposed to yield. The
results of this were often disastrous.
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Typical signal display for conventional permissive left turn.
Drivers generally
understand to yield when turning left in this situation.
However, the signal phasing could result in a "Yellow Trap". |
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"Dallas
phasing" signal display for
permissive left turn when oncoming traffic has a green signal for
through traffic and a protected left. Note the louvers in the left
turn lane through green
signal. While this solved the "Yellow Trap", drivers
sometimes misinterpreted
this to indicate a protected left turn.
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FYA to the rescue
In
addition to Dallas phasing, several other jurisdictions across the
country were experimenting with other types of displays for permissive
left turns. So to establish a national standard, federal traffic safety
officials began a study in the mid '90s to evaluate and select the best
permissive left signal. Various combinations of different colored
flashing and solid arrows and circular
signals were evaluated. The FYA, which had been widely used in Europe
for some
time,
was included in the evaluation.
In
driver comprehension studies, the FYA was found to
have a high inherent understanding. Perhaps more importantly, drivers
who did not understand its meaning tended to interpret it to
mean "wait", (i.e. a "safe failure") whereas with the green
circular signal,
drivers who misunderstood it usually interpreted it as a protected turn
(i.e. a "critical
failure".)
The
FYA also provided a signal indication that was exclusive for left
turns, i.e. it obviously had no meaning for through drivers, so
therefore seeing it would not possibly cause confusion for through
drivers.
And
the FYA proved to be more versatile and flexible
in terms of
possible
signal displays and operation than the other displays studied.
Based
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
did
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
The
FYA is instinctively understood by most drivers because of its
conformity 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 with
caution".
Safety studies
Several
studies of intersections where FYAs replaced legacy permissive left
turns have
consistently shown significant reductions in left turn crashes. One
study of 307 intersections in four states showed a 15-50% reduction in
such crashes, and another study of 222 intersections in North Carolina
showed a 16-59% reduction in those crashes. (Links to those studies is below.)
Summary
While the problem of the Yellow Trap was mostly solved with Dallas
Phasing,
using the traditional green circular signal with Dallas
Phasing to
indicate a permissive
left had several problems that
resulted in drivers turning when it wasn't safe, as well as
problems at
intersections with span wires, far side signal requirements, or
other
geometry
that made the use of the required louvered signals difficult or
impossible. Additionally, other signal options could cause driver
confusion in certain circumstances and also had other operational
issues. The FYA was determined to be the best solution for all of those
problems.
In short, here are the benefits of the FYA:
- Solves
the Yellow Trap
- Uses
a signal that is generally well-understood
- Uses
a signal that, if not understood, usually results in a safe outcome
- Uses
a signal that is flexible and can be used universally
- Uses
a signal that is exclusive for left turns
- Increases
left turn capacity, thus helping to reduce congestion and driver
frustration
- Reduces
crashes
Other
sites of interest
| 
Cable median barriers
