4.3. SR 04-19-1999 - Laserfiche WebLink

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. enforcement, safety is also improved if provisions are taken to minimize the possibility that vehicles will become trapped on the tracks behind a queue of vehicles or waiting for gaps in traffic at a parallel roadway immediately downstream from the grade crossing. For this reason, traffic control devices and traffic design in the vicinity of the grade crossing needs to include provisions to limit queuing on the tracks and to positively clear vehicles prior to the arrival of trains at the crossing. A wide range of measures is available to keep the crossing clear, including: . Roadway geometric features to provide vehicular storage downstream from the grade crossing Roadway shoulders to provide a refuge area downstream from the crossing Stop signs for frontage (parallel) roadway traffic at unsignalized intersections Use of active warning devices Use of "pre-signals" (traffic signals ahead of the grade crossing which turn red pnor to downstream traffic signals) Use of "queue cutters" (traffic signals ahead of the grade crossing which break the traffic flow into platoons which can clear the tracks) Use of "metering" of traffic from upstream traffic signals so that queuing on the tracks does not occur; and, Preemption of downstream traffic signals to provide track clearance phases. . . . . . . . Mobility Considerations at Grade Crossings Total vehicular delay accrues to each vehicle queued up while the crossing is blocked and continues to accrue until all of the vehicles in the queue have regained the initial travel speed. . For commuter rail-type grade crossings, given the relatively small blocking times per train, the total hourly impact of the crossing closure will typically be far less than the delay which occurs at signalized intersections along the cross street upstream and downstream from the grade crossing. The operating plan anticipated for the Northstar commuter rail system is at the most 4 trains per hour. With about 35 seconds gate blocking per train, the hourly Volume/Capacity impact at the grade crossing would be 0.04, which equals an effective green time percentage of 96 percent. This can be compared to the typical maximum green time to total cycle time of 40 to 45 percent which is typically available to a major movement at a signalized intersection. Therefore, the hourly impact to traffic at a Northstar commuter rail grade crossing is minimal. In addition to the average hourly impact, additional traffic operational impacts can occur when grade crossing closures impact platoons of vehicles which are moving through a progressive, coordinated traffic signal system. A portion of the platoon may be cut off and vehicles mayor may not be able to clear a downstream traffic signal in the green band when released from the grade crossing. Additional impacts may occur if an adjacent traffic signal is preempted in conjunction with grade crossing gate activation. Preemption is provided so that a traffic signal can provide a "track clearance" phase which will display a green signal indication to assure that vehicles on the trackway at the time of activation can clear off the tracks prior to train arrival. In addition, preemption sequences ordinarily provide a "limited service" phase which allows non-conflicting roadway movements to continue during gate blocking and train passage. Although preemption can provide benefits to parallel roadways, the traffic signal is randomly pulled out of coordination and the disruption to flow may extend to several signal cycles after train passage. . Commuter Rail Feasibility Study March 24, 1999 8-9 Social and Environmental Impacts