The in basket: Rob Shafer of Yukon Harbor in South Kitsap
writes, “The other day I was traveling west on Mile Hill Drive
approaching Woods Road when an ambulance approached from the other
direction.
“It appeared that all of the through traffic lights had been
triggered to red as cars were stopped in both directions and my
light was red. However, the left turn arrow on Mile Hill was still
flashing yellow where an inattentive driver could make a turn
directly in front of the emergency vehicle.
“Is there some fault with the emergency system where it does not
turn all lights red on the approach of the emergency vehicle? This
is not the first time I have seen this,” he said.
The out basket: Jeff Shea, traffic engineer in Kitsap County
Pubic Works,
says the signal was working as intended and explains what Rob
has seen.
“Emergency vehicle drivers are trained to watch out for
motorists that make illegal movements, such as turning in front of
an oncoming vehicle on a flashing yellow arrow,” Jeff said.
“We held several discussions with emergency vehicle operators to go
over this situation and make them aware of what the signal
configuration will (be).
“When a signal is ‘preempted’ for an emergency vehicle the whole
intersection does not go red. The direction the vehicle is
traveling will go green while the side and opposing traffic will
get red indications, except for the flashing yellow arrow in the
opposing direction.
“The reason the flashing yellow arrow continues to flash is to
avoid what is called the ‘yellow trap.’ The yellow trap
occurs when a left turning vehicle with a green ball or yellow
flashing arrow gets a steady yellow ball and assumes that oncoming
traffic is also getting the yellow ball and turns in front of that
vehicle assuming that it is coming to stop for the upcoming red
light. This condition caused so many collisions that the
federal guidance manual, the Manual on Uniform Traffic Control
Devices, specifically restricts agencies from configuring signal
systems to allow this.
“Therefore, we continue the flashing yellow arrow, and hope that
motorists obey both the legal requirements not turn in front of
traffic, or an emergency vehicle with its lights and sirens on.
“There is another option which requires us to terminate all the
movements that are going at the time of preemption. In this
situation, also, the MUTCD is very clear that we cannot shorten any
of the clearance times – the yellow and red times.
“So, by the time all those clearance times are complete and the
green ball comes back up for the preempted direction the emergency
vehicle may already be at or beyond the intersection making the
preemption. We felt this was not a good option.”