Advance Preemption Costs More than Simultaneous Preemption:Fact or Fiction?
Typical RR Preempted Intersection
Intersection Phasing Phase 6 Phase 1 8 Ped Phase 8 Phase 3 2 Ped 6 Ped Phase 7 Phase 4 4 Ped Phase 5 Phase 2
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)
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.
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.
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 CSD MTCD 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.
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
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 Total Approach Time is the SAME !
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)
Things That Do Affect Cost Vehicle – Gate Interaction Check • Additional Advance Preemption Time to keep gate from striking design vehicle