Transcript Slide 1

Advance Preemption Costs More
than Simultaneous Preemption:
Fact or Fiction?
Typical
RR Preempted
Intersection
Intersection
Phasing
8 Ped
Phase 7
Phase 4
Phase 8
Phase 3
MUTCD / AREMA Definition
Maximum Preemption Time
The maximum amount of time needed following initiation of
the preemption sequence for the highway traffic signals to
complete the timing of right-of-way transfer time, queue
clearance time, and separation time.
MPT = RWTT + QCT + ST
MUTCD / AREMA Definition
Right-of-Way Transfer Time (RWTT)
The maximum amount of time needed for the worst case
condition, prior to display of the track clearance green
interval. This includes any railroad or highway traffic signal
control equipment time to react to a preemption call, and
any traffic control signal green, pedestrian walk and
clearance, yellow change, and red clearance intervals for
conflicting traffic.
Receive Preemption Request
•Phase 2 Minimum Green (7 seconds)
•Phase 2 WALK (7 seconds)
Right-of-Way Transfer Time
•Phase 2 Minimum Green (7 seconds)
•Phase 2 Pedestrian Change (23 seconds)
Right-of-Way Transfer Time
•Phase 2 Yellow Change (4 seconds)
Right-of-Way Transfer Time
•Phase 2 Red Clearance (2 seconds)
Right-of-Way Transfer Time
WALK
0 seconds
Flashing DONT WALK
23 seconds
YELLOW Change
4 seconds
RED Clearance
2 seconds
TOTAL Right-of-Way Transfer
29 seconds
MUTCD / AREMA Definition
Queue Clearance Time (QCT)
The time required for the design vehicle of maximum length
stopped just inside the minimum track clearance distance to
start up and move through and clear the entire minimum
track clearance distance.
Minimum Track Clearance Distance (MTCD)
The length along a highway at one or more railroad tracks,
measured either from the highway stop line, warning device,
or 12 ft perpendicular to the track centerline, to 6 ft beyond
the track(s) measured perpendicular to the far rail, along the
centerline or edge line of the highway, as appropriate, to
obtain the longer distance.
MTCD
Clear Storage Distance (CSD)
The distance available for vehicle storage measured between
6 ft from the rail nearest the intersection to the intersection
stop line or the normal stopping point of the highway.
CSD
Queue Start-up Distance (L)
The maximum length over which a queue of vehicles
stopped for a red signal indication at an intersection
downstream of the crossing must get in motion so that the
design vehicle can move out of the railroad crossing prior to
the train’s arrival. The sum of CSD and MTCD.
MTCD
CSD
L
Queue
Clearance
Distances
MTCD CSD
L
Design Vehicle
The longest vehicle permitted by statute of the road
authority (State or other) on that roadway.
55’
65’
Maybe even longer….Double or Triple Trailer ?
Why do we need to clear the
tracks? Everybody knows not
to stop on the tracks. There’s
even a sign.
Queue Clearance (First Component)
Queue Start-up – Time elapsed after beginning of track clearance
green until design vehicle can start moving. All red vehicles must
move before design vehicle (yellow truck) can begin to accelerate.
Queue Clearance (Second Component)
Design Vehicle Clearance – Time required for design vehicle to
accelerate from a stop and travel through and clear of MTCD.
Queue Clearance Time
Queue Start-up
6 seconds
Time before design vehicle begins to move
Calculate as 2 + (L/20)
Design Vehicle Clearance
14seconds
Time for design vehicle to accelerate
through design vehicle length and MTCD
TOTAL Queue Clearance
20 seconds
MUTCD / AREMA Definition
Separation Time (ST)
The component of maximum highway traffic signal
preemption time during which the minimum track clearance
distance is clear of vehicular traffic prior to the arrival of the
train.
Separation Time
Design vehicle allowed to move more than 6 ft clear of MTCD prior to
train arrival.
4 sec ST
Train Arrival
Maximum Preemption Time
Right-of-Way Transfer Time
29 seconds
Queue Clearance Time
20 seconds
Separation Time
TOTAL Max Preemption Time
4 seconds
53 seconds
RR Warning Times
Simultaneous Preemption
Set RR Minimum Warning Time equal to
Maximum Preemption Time.
MWT = MPT
Advance Preemption
Set Advance Preemption Time equal to
Maximum Preemption Time minus RR
Minimum Warning Time
MWT = 20
APT = MPT - 20
RR Warning Times
Simultaneous Preemption
Advance Preemption
Minimum Time
20
Minimum Time
20
Clearance Time
33
Clearance Time
0
Buffer Time
5
Buffer Time
5
Equipment Response
5
Equipment Response
5
Advance Preemption
0
Advance Preemption
33
Total Approach Time
63
Total Approach Time
63
Total Approach Time is the SAME !
Time Line Comparison
29 Second RWTT
Things That Do Affect Cost
Right-of-Way Transfer Time
• Minimum Green (engineering judgment)
• Walk (omit or shorten permitted by MUTCD)
• Pedestrian Change (omit or shorten permitted
by MUTCD)
Time Line Comparison
11 Second RWTT
Things That Do Affect Cost
Vehicle – Gate Interaction Check
• Additional Advance Preemption Time to keep
gate from striking design vehicle
Time Line Comparison
29 Second RWTT with VGI
Time Line Comparison
11 Second RWTT with VGI
Questions?
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