Combination Effects of Public Transport Priority Measures
thesis
posted on 2017-02-13, 01:16authored byLong Tien Truong
Public
Transport Priority (PTP) is crucial to improving Public Transport (PT) travel
time and travel time reliability. PTP can be categorised as Road-Space Priority
(RSP), e.g. Queue Jump Lane (QJL) and Dedicated Bus Lane (DBL), and Transit
Signal Priority (TSP). To increase its effectiveness, TSP may be combined with
RSP, e.g. TSP combined with DBL (TSPwDBL) or TSP combined with QJL (TSPwQJL). There
has been a growing body of literature on the design and operation of PTP
measures. Yet, no research has been undertaken to establish whether combining
TSP with RSP measures creates an over-additive effect where the combined
treatment effect is greater than the sum of their separate effects. In
addition, it remains unclear whether providing PTP measures at multiple
locations, e.g. road sections and intersections, along a signalised arterial
creates a multiplier effect where the effect from providing PTP measures at
multiple locations is greater than the sum of effects from providing PTP
measures at each of those individual locations.
This thesis therefore aims to provide an in-depth
understanding of the combination effects of PTP measures. A research approach
with six components is adopted. The first four components focus on
methodological developments, which are then applied for understanding the
combination effects in the last two components.
Traffic Micro-simulation Models (TMMs) are selected as an
experimental tool for this research. The first component develops new methods
to calculate the Minimum Number of Runs (MNR) required to estimate multiple
Measures of Performance (MOPs) at an overall confidence level, using multiple
comparisons in statistical theory. Numerical analyses based on an example
corridor suggest that new methods provide an improved means of assessing the
statistical accuracy of multiple MOPs.
Given the impacts of signal coordination on the performance
of PTP measures on arterials, it is crucial to investigate their combination
effects when signal offsets are optimised. Hence, the second component proposes
new offset optimisation models, which consider randomness in bus dwell time and
PTP measures such as DBLs and QJLs. In these models, bus and general traffic
delays are estimated using kinematic wave theory. Validation using TMMs
demonstrates the effectiveness of these new models.
Bus delay functions can be used as a PTP planning tool and to
examine the effects of combining TSP with RSP measures at an intersection
level. Thus, the third component proposes a set of kinematic wave theory-based
delay functions to estimate bus delay effects for a range of PTP measures (i.e.
DBL, QJL, TSP, TSPwDBL, and TSPwQJL). Delay associated with bus acceleration is
also approximated. Validation using TMMs indicates an acceptable level of
agreement between delays obtained from new delay functions and TMMs.
While this thesis focuses on the effects of combining
conventional (local) TSP control at multiple intersections, it is also prudent
to examine whether a coordinated TSP control model, which considers bus
progression through multiple intersections, performs better than providing the
conventional TSP control model at those intersections. The fourth component
therefore develops a coordinated TSP control model considering arterial
progression and stochastic bus arrival time. Extensive TMM experiments show
that the coordinated TSP control generates an additional reduction in bus delay
of 11% to 19% when compared to conventional TSP control.
In the fifth component, kinematic wave theory-based analyses,
together with new bus delay functions, suggest that at an intersection level,
the effects of combining TSP with RSP measures on bus delay savings are smaller
than additive if there is no nearside bus stop and the traffic condition in the
base case is under-saturated. With a near-side bus stop, the combined treatment
effect on bus delay savings at an intersection level can be over-additive, depending
on various factors, e.g. dwell time and distance from the bus stop to the stop
line. In addition, analytical results indicate that at an arterial level, the
combined treatment effects on bus delay savings can be over-additive with
suitable signal offsets. These results are confirmed by a TMM case study. The
over-additive effects of TSP with DBLs or QJLs result in an 8-28% increase in
bus delay savings, when compared to an additive effect.
In the sixth component, TMM results reveal that providing PTP
measures (i.e. QJL, TSP, TSPwDBL, and TSPwQJL) at multiple locations can create
a multiplier effect on one-directional bus delay savings, particularly when
signal offsets provide bus progression for that direction. In general, the
multiplier effect results in a 4-8% increase in bus delay savings for each
additional road section or intersection with PTP measures, when compared to a
Constant Returns to Scale (CRS) effect. A reason for the multiplier effect on
bus delay savings is that PTP measures reduce the variation in bus travel
times. This enables signal offsets, which account for bus progression, to
perform even better, particularly when the variation in bus dwell times is not
high.
This thesis provides six original contributions to knowledge
in line with the six research components. Overall, it is concluded that
combining PTP measures, either TSP with RSP measures or PTP measures at
multiple locations on signalised arterials, will help to improve travel times
and reliability for PT passengers, ultimately enhancing the PT user experience.