2012 Minnesota DOT – ACEC Annual Consultant Conference
Alternatives to Advanced Preemption at Railroad Crossings
2012 Minnesota DOT – ACEC Annual Consultant Conference
What is Railroad Preemption at a Grade Crossing?
2012 Minnesota DOT – ACEC Annual Consultant Conference
Railroad Preemption:A special control mode in a traffic signal controller designed to start up and clear any vehicular traffic on the roadway approach crossing the railroad tracksThen allows only traffic movements that do not conflict with the railroad for the duration of the train movement
2012 Minnesota DOT – ACEC Annual Consultant Conference
8 3
7 4
25
16
1. Terminate any allowable combination of phases and associated pedestrian movements.
2012 Minnesota DOT – ACEC Annual Consultant Conference
8 3
7 4
25
16
2. Display Green for Track Clearance Movements and hold in Green until railroad gates are down.
2012 Minnesota DOT – ACEC Annual Consultant Conference
8 3
7 4
25
16
3. Allow only those phases or movements that do not conflict with crossing until preemption ends.
2012 Minnesota DOT – ACEC Annual Consultant Conference
8 3
7 4
25
16
3. Allow only those phases or movements that do not conflict with crossing until preemption ends.
2012 Minnesota DOT – ACEC Annual Consultant Conference
8 3
7 4
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3. Allow only those phases or movements that do not conflict with crossing until preemption ends.
2012 Minnesota DOT – ACEC Annual Consultant Conference
What is Advanced Preemption?
2012 Minnesota DOT – ACEC Annual Consultant Conference
Advanced Preemption is an operating mode which allows the traffic signal to display
green to clear the track before the railroad flashing lights
begin to operate
2012 Minnesota DOT – ACEC Annual Consultant Conference
8 3
7 4
25
16
1. Track clearance green interval begins
2012 Minnesota DOT – ACEC Annual Consultant Conference
8 3
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2. Railroad warning devices begin to operate
2012 Minnesota DOT – ACEC Annual Consultant Conference
8 3
7 4
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3. End track clearance green
2012 Minnesota DOT – ACEC Annual Consultant Conference
That seems simple enough, what’s the issue here?
2012 Minnesota DOT – ACEC Annual Consultant Conference
When preemption is implemented, adequate time must be provided in order to permit a Design Vehicle to
clear the crossing prior to the arrival of the train75’ in MN
2012 Minnesota DOT – ACEC Annual Consultant Conference
So how much time does it
take for preemption to
operate?
In this example, 52 seconds is
required.
101’
2012 Minnesota DOT – ACEC Annual Consultant Conference
Minimum Green = 7 secondsPedestrian Change = 29 seconds
Yellow Change = 4 secondsRed Clearance = 2 seconds
32 seconds of Advanced Preemption Time required at this location
2012 Minnesota DOT – ACEC Annual Consultant Conference
The required amount of time
must be provided by the
railroad train detection circuitry
2012 Minnesota DOT – ACEC Annual Consultant Conference
MUTCD requires that the
railroad must provide a
minimum 20 seconds of
warning prior to the arrival of a through train
2012 Minnesota DOT – ACEC Annual Consultant Conference
Any time required
beyond the minimum
warning time prior to the
arrival of a train becomes an addition to a basic warning system project
2012 Minnesota DOT – ACEC Annual Consultant Conference
In a nutshell..
Time=
$$$
2012 Minnesota DOT – ACEC Annual Consultant Conference
Why?1.Substantial additional circuitry due to electrical design limitations of the train detection equipment2.Railroad train control signal system must co-exist with crossing systems3.Remote equipment locations which may be 1000’s of feet from the crossing4.Extensive underground cabling to remote locations
2012 Minnesota DOT – ACEC Annual Consultant Conference
What are the alternatives to advanced preemption or
lengthy advanced preemption times?
2012 Minnesota DOT – ACEC Annual Consultant Conference
Turn off the traffic
signal
Effective?
Practical?
2012 Minnesota DOT – ACEC Annual Consultant Conference
Grade Separate
the Crossing
Even more $$$
2012 Minnesota DOT – ACEC Annual Consultant Conference
Close the Crossing
Never a popular
choice with local
politicians
2012 Minnesota DOT – ACEC Annual Consultant Conference
Practical Engineering Solutions
2012 Minnesota DOT – ACEC Annual Consultant Conference
Pedestrian TreatmentsCrosswalk Elimination
2012 Minnesota DOT – ACEC Annual Consultant Conference
From our example, the Pedestrian Change Time is 29
seconds
Engineering changes to the intersection can reduce the
time required from the railroad
2012 Minnesota DOT – ACEC Annual Consultant Conference
In many cases, there is no sidewalk present
between the track and the
parallel roadway
2012 Minnesota DOT – ACEC Annual Consultant Conference
Eliminate the crosswalk
parallel and closest to the
track
Can save 2 – 4 seconds of pedestrian
change time
2012 Minnesota DOT – ACEC Annual Consultant Conference
Pedestrian TreatmentsRefuge Islands
2012 Minnesota DOT – ACEC Annual Consultant Conference
Installing pedestrian refuge islands to shorten the distance and
required pedestrian clearance time
2012 Minnesota DOT – ACEC Annual Consultant Conference
This permits the required pedestrian
clearance time to be reduced by
approximately 50% depending on
crosswalk lengths
2012 Minnesota DOT – ACEC Annual Consultant Conference
New TechnologyQueue Cutter Signal
2012 Minnesota DOT – ACEC Annual Consultant Conference
A Queue Cutter Signal is the most cost effective tool
available to reduce advance preemption time
2012 Minnesota DOT – ACEC Annual Consultant Conference
A Queue Cutter Signal is a separate traffic control signal installed at a grade crossing
2012 Minnesota DOT – ACEC Annual Consultant Conference
A queue cutter signal is not connected to or operated as a part of a
downstream signalized intersection
2012 Minnesota DOT – ACEC Annual Consultant Conference
Generally, a queue cutter signal is installed where the Clear Storage
Distance exceeds 400 - 450’
2012 Minnesota DOT – ACEC Annual Consultant Conference
Queue Loops
Queue loops must use fail-safe design and vital loop processor system
Each loop wire has 2 independent loop circuits – a detect loop and a check loop
Queue cutter signal flashes red if there is a loop system failure
Varies200 – 250’
Typical Queue Cutter Signal Layout
2012 Minnesota DOT – ACEC Annual Consultant Conference
Queue Cutter Signal
inLos
Angeles
2012 Minnesota DOT – ACEC Annual Consultant Conference
Queue Cutter Signal
inLos
Angeles
2012 Minnesota DOT – ACEC Annual Consultant Conference
2012 Minnesota DOT – ACEC Annual Consultant Conference
It is interconnected with the railroad warning system with a small amount
of advance preemption time
This allows time for the queue cutter to change to red before the railroad
flashing lights activate
2012 Minnesota DOT – ACEC Annual Consultant Conference
2012 Minnesota DOT – ACEC Annual Consultant Conference
2012 Minnesota DOT – ACEC Annual Consultant Conference
2012 Minnesota DOT – ACEC Annual Consultant Conference
When is a Queue Cutter not a Queue Cutter?
When it’s a Pre-Signal
2012 Minnesota DOT – ACEC Annual Consultant Conference
Installed like a Queue Cutter
Looks like a Queue Cutter
Too close to the downstream intersection to use queue
detection
2012 Minnesota DOT – ACEC Annual Consultant Conference
A Pre-Signal still requires full Advanced Preemption Time
from the railroad
Why?
2012 Minnesota DOT – ACEC Annual Consultant Conference
Confusing to road users – is it a pre-signal or near-side
signal faces?
Do I wait here or can I make a right-turn-on-red?
2012 Minnesota DOT – ACEC Annual Consultant Conference
Pre-Signal ornear side
signal faces?
2012 Minnesota DOT – ACEC Annual Consultant Conference
CLOSING THOUGHTS
Remember – Preemption operation is not as easy as it appears on the surfaceRecognize – You need professional help to understand and properly design the systemUnderstand - Connecting 2 independent systems produces a third, more complex systemGrasp - The railroad is your friend – REALLY!Plan - It will take longer and cost more than you think.
2012 Minnesota DOT – ACEC Annual Consultant Conference
Questions?
Rick CampbellCTC, Inc.