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_Best Paper_ Queue Jumper Lanes - Aaron Zhou

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_Best Paper_ Queue Jumper Lanes - Aaron Zhou Powered By Docstoc
					           Queue Jumper Lanes: A Strategy for Improving Transit Performance?
                       Aaron Zhou, Florida International University

Increasing need for more efficient use of limited roadway space has led to the promotion of
preferential treatments for high-occupancy buses. The designation of bus lanes and the provision
of transit signal priority (TSP) on arterial streets are two major bus preferential treatments that
have received increasing attention in North America. In practice, however, it is often difficult to
justify the use of an exclusive lane for buses during peak hours. Studies have also shown that
TSP is ineffective during peak hours because buses are not able to by-pass the long waiting
queues typical of these hours. While priority for buses is needed the most during peak hours, the
treatments that have been the focus of recent research are either ineffective or difficult to justify
for these hours. This paradox has had a limiting effect on the applications of bus lanes and
regular TSP in practice.

A special type of bus preferential treatment that has the potential of avoiding the shortcomings of
both bus lanes and regular TSP is queue jumper lanes. This treatment usually combines a short
stretch of special lane with signal priority to allow buses to by-pass a waiting traffic queue
through the use of a right-turn bay and then to cut out in front of the queue by getting an
exclusive green signal. The figure below shows an intersection with a queue jumper design that
includes a right-turn bay that is shared by buses and right-turn vehicles, and an optional
downstream right-turn pocket to help buses to merge back into the mainline after crossing the
intersection. Unlike bus lanes, queue
jumper lanes do not take a lane away
from the general traffic, yet they enjoy
the queue bypassing ability of bus lanes
by making use of existing right-turn
bays that generally operate under low
saturation levels. The queue bypassing
ability of queue jumper lanes also
allows the bus arrival times at the stop                                               Legend
line to become more predictable, thus                                                  Queue jumper
reduce the probability of buses missing                                                Bus detector
                                                                                       Pavement marker
the priority signal.                                                                   Bus stop


For queue jumper to operate effectively, however, the right-turn bay must be accessible to the
arriving buses, i.e., the entrance to the bay must not be blocked by the standing queue waiting to
clear the intersection. In theory, the probability of a turn-bay blockage can be reduced by
increasing the length of the bay. In reality, however, this length is often constrained by the
limited right-of-way typical of the urban settings. This is one main reason that queue jumper
lanes have not received more widespread use. Fortunately, it is possible to overcome this
limitation by adjusting the signal timing such that the probability a turn-bay of a specific length
is blocked is minimized while keeping the impact to the side street traffic to the minimum.

Queue jumper lanes combined with optimal signal design with priority can potentially be an
effective solution to improving transit operation at urban signalized intersections, thus increase
transit attractiveness in congested areas like the South Florida. They deserve to be given a closer
look.

				
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posted:10/1/2011
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