Assessing travel time impacts of measures to enhance bus operations.

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Jepson, D., Ferreira. L. (1999).Assessing travel time impacts of measures to enhance bus operations.
Part I: past evidence and study methodology. Road & Transport Research Journal, 8 (4), 41-54.
Paper submitted to Road & Transport Research
Title: Assessing Travel Time Impacts of Measures to Enhance Bus Operations.
Part I: Past Evidence and Study Methodology
Authors: Dale Jepson 1 and Luis Ferreira2
Address for correspondence: Dr Luis Ferreira, AHURI, QUT, P O Box 2434, Brisbane, QLD
4001
Email: L.Ferreira@qut.edu.au
ABSTRACT
There have been a variety of bus priority measures used for at least 25 years in various areas
throughout the world. European countries, particularly the UK, have pioneered many of the
bus priority systems on arterial streets. Many of the systems associated with freeway
operations have been developed in the United States. Bus lanes and traffic signal priority are
the most common forms of bus priority and these systems can provide significant travel time
savings for congested arterial roads.
This paper presents the main findings regarding evidence from past work and the
methodology used in a recent study that focused on the efficiency of the overall journey time
of bus transport on arterial roads. The analysis of the various treatments will focus on
reducing travel time for buses, which is fundamentally linked to the cost and efficiency of
this form of public transport. The work undertaken considers the travel time savings obtained
for buses and the associated impacts on the remainder of the general purpose traffic to
minimise the person delay through the network. The inclusion of other parameters that may
affect the justification of bus priority measures such as vehicle costs and the environmental
costs is a logical extension of this research.
A methodology for the selection of bus priority is outlined in this paper. This is based on
detailed analysis of the travel time impacts of various bus priority treatments. However, it is
stated that the selection process should entail the consideration of these issues in conjunction
with the wider transport planning context. Furthermore, this paper recommends that bus
priority treatments be part of an overall traffic management strategy for a transport corridor.
It is suggested that there may be significant travel time savings associated with bus priority
treatments. However to obtain these benefits with manageable impacts on other traffic, the
type and nature of the bus priority treatments need to be matched to the road and traffic
conditions. This will ensure that the efficiency of the road infrastructure is maximised for
each traffic management strategy.
1
2
Senior Traffic Engineer, Queensland Dept. Main Roads
Associate Professor in Transportation, Queensland University of Technology
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1. INTRODUCTION
It is recognised that the increasing costs of traffic congestion needs to be addressed through
an integrated multi-modal transport system. The savings to the community in facilitating a
shift to public transport can be significant, particularly in urban peak congested conditions.
This may be enhanced through enhancements to the service provided by public transport.
Improvements to public transport may be considered through a number of avenues including
improving vehicle efficiency, integration of transport modes, reduction of the cost of service,
reductions in travel times and in comfort for passengers.
Bus operation efficiency is examined here through single trip journeys for buses on arterial
roads to investigate techniques for improving this form of transport. The work reported here
was part of a research project, which analysed the travel time savings obtained for buses and
the associated impacts on other traffic, in order to minimise the person delay through the
network.
Whilst optimising person delay is one of the most significant transport goals, it is
acknowledged that there are other issues that may influence the decision to implement bus
priority treatments. The impact on bus operating costs, the environmental benefits of public
transport and the management of demand for private vehicles, are three of the substantial
issues that would affect this process. The current analysis was undertaken at a micro level for
a specific route and examines only travel time issues. The effects of vehicle operating costs
and environmental impacts are not included in this research.
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Section 2 of this paper provides a review of the existing practice for each of the main bus
priority measures under study, namely: bus lanes, signal priority, busways, transit lanes and
measures related to bus stop delays. Section 3 considers the assessment of bus priority
measures in the context of the wider transport planning objectives. Section 4 offers a brief
outline of the methodology used to assess bus priority measures. This is followed in section 5
by a summary of the main results obtained for bus priority implementation criteria. Finally, a
summary of the evidence reviewed is presented in section 6.
This paper represents Part I of a two part publication in this journal. Part II deals with the
development of assessment criteria for each priority measure and the detailed results
obtained, Jepson and Ferreira (1998).
2. PAST WORK
2.1 Background
The main components of the total bus journey time include the road travel time, delay due to
deccelaration/accelaration of buses stopping at bus stops and the delay associated with the
boarding/alighting of passengers. Bus travel time in urban conditions can be typically twice
the corresponding travel time for a car. Higginson et al. (1995) describes a case study for a
number of areas of the United Kingdom where the journey time for a bus varies from 1.8 to
2.5 times the corresponding journey time for a car.
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The road travel time for arterial roads is influenced by delays associated with road geometry,
traffic control devices (eg. traffic signals, roundabouts) and interactions with other vehicles.
The travel time function has been considered in Australia by Davidson (1978), Akcelik
(1991) and Tisato (1991). The prediction of travel time is important in evaluating the effect
of changes in traffic conditions. In situations of high vehicle flows there is increased
interactions with other traffic and the delays are higher for vehicles using the route. In these
circumstances the benefits of bus priority treatments are the most significant.
The travel time effects for buses and general purpose traffic are considered for the main bus
priority treatments used throughout the world. This paper considers the important issues in
selected bus priority treatments. Typical applications and the assessment is considered below.
2.2 Bus Lanes
Bus lanes can be divided in two distinct categories, namely: those that share part of the
arterial road space with general traffic; and streets/malls that are designated exclusively for
buses, Fuhs (1993). Turnbull (1992a) indicates there are over 500 km of bus lanes in various
cities throughout Europe including 200 km in Paris. Furthermore, London Transport (1997)
advise there is currently 95 km of bus lanes in London, and it is proposed to extended the
length of bus lanes to 500 km. Bus lanes are less common in North America with typical
applications involving the re-designation of a parking lane during peak hours to facilitate bus
movements. Australia has similar applications of with-flow bus lanes to other parts of the
world. With-flow bus lanes in Australia may be found in most
major cities including
Brisbane, Adelaide (Foley et al., 1980), Melbourne (Piper and Cornwell, 1986) and Sydney
(Luk,1992).
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The set-back of the bus lane from a signalised intersection is an issue that is considered in
some detail primarily in the United Kingdom. This treatment operates as a with-flow bus
lane, that is discontinued a specific distance from the intersection. This allows buses midblock priority, though they travel through the signalised intersection mixed with general
traffic. There are numerous examples of this treatment in the United Kingdom.
A bus lane in the median lane is used across the Sydney Harbour Bridge as a line haul service
into Sydney CBD, Quail and West (1992). A contra-flow median bus lane is also used on the
Auckland Harbour Bridge, Wilson and Houghton (1996). Other examples of median bus
lanes in North America are in Broadway, Denver; Barbour Blvd, Portland; and Dixie
Highway, Miami, Levinson (1987).
Evaluation of Bus Lanes
As bus lanes have been operational for over 25 years in Europe, these facilities have become
an accepted form of bus priority. There was substantial research undertaken in Europe in the
1970s regarding the justification of bus lanes. Bly et al. (1978) indicated that bus lanes would
provide appreciable benefits when the degree of saturation is greater than 90 percent, though
they may be justified at lower flow rates. According to Oldfield et al. (1977), a bus flow of in
excess of 120 buses/hour is needed to justify a bus lane with no set-back at traffic signals.
Furthermore, a degree of saturation above 0.9 is required to justify bus lanes with set-back at
traffic signals.
In the United Kingdom, there are various warrants developed for implementation of bus
lanes. These warrants give a ‘rule of thumb’ guidance, though more detailed analysis has
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been undertaken using traffic modelling. Oldfield et al. (1977) provides direction in
undertaking economic analysis of bus lanes in the United Kingdom. Their approach weighs
up the person travel time and bus vehicle savings against the additional time for private cars.
The resultant
model used equations for queue lengths and simulates the behaviour of
individual vehicles. Robertson (1985) discusses the need for the effects of bus lanes to be
quantified, as achieved in West Yorkshire.
There have been over 20 bus lane treatments changed or taken out in North America for a
variety of reasons, Batz (1986a). The Transportation Research Board (1994) published
criteria for assessing the need for with-flow, kerb-side bus lanes for applications in the
United States. This indicates that bus lanes would be warranted where minimum one-way bus
volumes are 30 - 40 / peak hour, carrying passenger volumes of around 1200
passengers/hour.
There is limited work undertaken in Australia dealing with guidelines for the justification of
bus lanes. Austroads (1991b) discusses the benefits of bus lanes but it does not provide
guidelines for the assessment of these facilities. Taylor (1996) provides information on bus
lane warrants based on the work by Vuchic (1981), which suggests that a bus lane should
carry at least the number of passengers as adjacent general purpose lanes.
2.3 Priority to Buses at Signals
There are two categories of treatments available to allow buses priority at traffic signals,
namely active and passive priority. Active priority entails each bus being selectively detected
prior to an intersection and adjustments made to the signals to enhance bus progression.
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Passive priority involves adjustment of the traffic control system to suit the bus schedules for
that route. These methods of traffic signal priority are considered separately.
Active Priority
Whilst this treatment has been used for over twenty years, the more recent developments in
technology have resulted in significant advancements in this area. Existing modern systems
allow real-time detection of buses as an input into sophisticated Urban Traffic Control
Systems. Whilst this is based on relatively recent technology, forms of active priority systems
have been operational in excess of 25 years.
Active bus priority in the United Kingdom started in 1971 with a trial in Leicester. However,
the number of active bus priority schemes were limited due to the extra delays to general
traffic, Hounsell and McDonald (1988). The ‘SELKENT’ system in London, which started in
1987, was the most significant example of selective detection, Hounsell (1995). Fox (1995)
describes a trial in Leeds where a system of bus priority, starting and stopping wave queue
management and speed advice to facilitate progression, was implemented. This trial, which
used radio frequency identification for bus recorded bus travel time savings of up to 8 per
cent with this form of priority (Fox et al. 1995).
Other bus priority systems at traffic signals are used in many areas throughout Europe with
Bishop (1994) identifying over 20 cities with these systems. The systems in Turin and
Gothenburg are part of the ‘PROMPT’ project, which is a major undertaking in Europe to
evaluate the effects of various traffic management systems, Hounsell (1995). Nelson et al.
(1993) describes the trial at the Corso Grosseto in Turin, where an overall traffic management
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scheme has been devised that includes bus priority and bus stop rationalisation. This project
is claiming reductions in bus travel time of between 2 per cent and 7 per cent with reductions
also experienced by private traffic, Biora (1995).
There are a number of examples within the United States of active priority or signal preemption as it is commonly known in that country. Batz (1986a), in a study of all high
occupancy vehicle treatments, found that there were sixteen instances of signal pre-emption
systems in the United States. However, over half of those systems have been suspended due
to a number of reasons, including perceived lack of benefit to buses with large delays to
general traffic. The advancements in technology have prompted several recent instances of
active signal priority in North America. These include systems in Minneapolis and Portland.
The system in Portland trialed bus priority on a major arterial road carrying 40000 - 50000
vehicles per day and provided priority using green extension/ early green return or queue
jump priority for buses, Kloos et al. (1994). Minor reductions in bus travel time have been
reported.
There are examples of active priority in most of the larger Australian cities including
Brisbane (Campbell and Miorandi, 1997); Sydney (Mehaffey and Lowe, 1997 and Moore,
1978); and Melbourne (Wisdom, 1990). Brisbane City Council are using selective vehicle
detection on a major western arterial into Brisbane’s CBD, Campbell and Miorandi (1997).
Active bus priority is also used in other parts of the world, though less widespread than that
experienced in European countries. Turnbull (1992a) indicates examples are located in Japan,
Hong Kong, Singapore and South Africa. The results are similar throughout the world with
increasing emphasis on this form of priority as traffic signal technology improves.
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A variety of computer models have been used to determine the effects of bus priority
(TRANSYT (Vincent et al.,1980); NETSIM (Taylor and Al-Sahili, 1995); NEMIS (Fox et
al., 1995); and SATURN (Willumsen et al., 1993). The literature indicates modest savings to
buses with traffic signal priority. The technology that is allowing active bus priority at traffic
signals involves real-time communication between buses, ticketing systems and traffic signal
control systems. The centrally controlled integration of real-time passenger information, bus
timetables, real-time bus progress, general traffic conditions and variable message signs has
potential to significantly improve arterial road operations. Using algorithms in a central
computer, priority may be given to buses based on their current operational and passenger
occupancy status.
Passive Priority
Passive priority includes adjustment of traffic signal settings, such as adjusting the cycle
time, splitting phases; or area-wide timing plans. Traffic signal design using this philosophy
does not detect individual buses to provide priority. Rather, it increases the probability of a
bus receiving minimal delays at traffic signals by increasing the green time for a route
travelled by buses.
A recent example of passive priority involves a site in West London, which is using a
metering technique to control the queues of general traffic to minimise the impacts on bus
operations, Oakes and Metzger (1995). This treatment has been modelled and it was
predicted that there will be a small increase in queue length for general traffic with
significant delay savings for buses. The disadvantages of providing extra priority to a bus
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route include the potential increase in delay to traffic on routes that are not designated bus
routes.
Other passive priority techniques, such as permitting buses to undertake turns restricted for
general traffic or metering of traffic flows, can be effective with no significant disruptions to
general traffic. In low bus flow situations, allowing buses to undertake restricted turns can
have negligible impact on the general traffic capacity. Similarly, the use of bus pre-signals is
a practical means of providing priority to buses in locations where there is congestion at a
confined area, such as a reduction in traffic lanes.
2.4 Busways
Martinelli (1996) defines busways as access controlled facilities that are dedicated for buses
and provide a high standard carriageway separated from the general purpose lanes. Many of
the busways are high speed facilities with grade separated access. However, busways may
also be constructed in a lower speed environment adjacent to arterial roads. There are a
relative small number of major busway facilities operating throughout the world. The two
notable examples in North America are in Ottawa and Pittsburg, Fuhs (1993). Turnbull
(1992a) identified 6 exclusive busway facilities with separate ‘right-of-way’ operating
outside North America. These facilities are located in Adelaide (Australia), Essen (Germany),
Istanbul (Turkey), Port of Spain (Trinidad), Redditch (Great Britain) and Runcorn (Great
Britain). Other facilities are located in Perth, (Western Australia ) on the Kwinana freeway as
indicated by Middleton (1994). These facilities would all appear to be working successfully,
with the primary aim of providing a high level of service for line haul bus commuters. A
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further busway is being planned in Australia to improve the travel time for passengers
travelling to and from the Brisbane CBD area.
2.5 Transit Lanes
The use of multi-purpose transit lanes permit high occupancy vehicles (including buses) to
use designated lanes that operate at a higher level of service than the general purpose lanes.
Vehicles with 2 or more occupants, or 3 or more occupants, are the most common occupancy
requirements for such lanes. Turnbull (1992b) identified 10 major transit lane facilities on
freeways and a similar number of transit lanes on arterial roads outside North America. Batz
(1986a) found 95 examples of concurrent flow arterial preferential lanes, which have been in
operation for various periods in North America. Of these facilities in North America, 22 were
suspended due to low utilisation and a high numbers of violations.
There has been significant work done in the United States evaluating transit (HOV) lanes for
the freeway environment. The warrants are predominantly based on maximising person
throughput for a roadway. Nurworsoo et al. (1988) proposes that a HOV lane should provide
a minimum travel time saving of 1 minute/mile with an overall travel time saving of at least 7
minutes for a HOV lane to be effective. Nuworsoo et al. (1988) suggests that the maximum
volume of traffic using a HOV lane should not exceed 1000 vehicles per hour, which equates
to a level of service ‘B’ from the Highway Capacity Manual, Transportation Research Board
(1994).
2.6 Other Treatments to Improve Bus Journey Time
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As a significant proportion of the total bus journey time is associated with buses stopping to
allow passengers to board and alight, this area is an important component of the total journey
time analysis. Improved ticketing systems, loading times, reduce customer inquiry, reduce the
number of bus stops and rationalisation of bus stop locations are all examples of treatments
that may increase bus travel efficiency. For Australian conditions, Taylor (1996) found that
approximately 25 percent of the riding time is taken up with the bus stationary at bus stops.
The ticketing systems used by bus operators, the level of passenger enquires and the physical
arrangement for entering/leaving a bus, are the major factors affecting the dwell time at bus
stops.
Bus Stop Relocation
The location of bus stops can be critical to the efficiency of the bus system. Factors such as
traffic volumes, passenger demand, adjacent land use and road geometric conditions must be
considered in siting a bus stop. The location of the bus stop becomes an even more important
in areas where there are bus priority systems. Hounsell (1988) describes the issues in bus stop
location on arterial roads used in conjunction with bus priority. In general terms, the bus stop
location must complement the aim to enhance bus operations.
Bus Stop Spacing
Watry and Mirabdal (1996) discusses a program to rationalise bus stops in San Francisco,
where the bus stop spacing was increased from between 120 m - 250 m to 250 m - 300 m.
These changes resulted in a 40 per cent reduction in bus stops and an increase in overall bus
travel speeds of between 4 and 14 per cent. The spacing of bus stops requires a balance
between bus travel efficiency and passenger convenience in accessing bus stops. The
relationship between convenience and efficiency may be modelled to determine the
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appropriate spacing of bus stops. It is generally expected that bus stops should be located
between 200 metres and 500 metres apart. The minimum spacing of 200 metres was
calculated by Pretty and Russell (1988) based on Australian conditions, using typical
acceleration, deceleration and stop times for a bus.
Reducing time Spent at Bus Stops
Savings through minimisation of the time to purchase tickets, would appear to represent the
most significant impact on the dwell time at bus stops. The supply of real time passenger
information has been gaining popularity in recent years. This can be used both as a tool to
improve the exposure of public transport and to reduce the delays with drivers answering
questions from infrequent bus users. Campbell and Miorandi (1997) discusses the use of
variable message signs with bus arrival data in Brisbane. This system is stated to be accurate
and is viewed favourably by passengers, though no detailed survey has been reported.
3. THE ASSESSMENT OF BUS PRIORITY TREATMENTS
The discussion on various world-wide practices of the bus priority treatments indicates a
plethora of treatments that may be used to provide priority for buses of which a sample have
been reported in this paper. The literature reviewed suggests the introduction of bus priority
measures for arterial roads should be part of a comprehensive and integrated traffic
management strategy. At the local arterial level, locations where bus priority measures may
be suitable should be identified taking into account overall demand management, as well as
road efficiency considerations. Figure 1 shows the linkages between the more specific
objectives of bus priority treatments, which are the subject of this paper, and the wider goals
which the same measures may help achieve.
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Public transport enhancements, such as those discussed here, need to be assessed in the
context of a set of strategies which have a time dimension, as well as those which involve
satisfying a range of objectives, which may be in conflict with each other. The time
dimension relates to the achievement of longer-term goals, in addition to the more directly
measurable short-term objectives, such as bus travel time and operating cost savings. What is
much more difficult to quantify with a reasonable degree of accuracy is the potential
contribution of those public transport measures to longer-term goals. Examples of the latter
are shifts away from private car usage and hence reduced levels of emissions from cars and
buses, as well as reduced energy consumption from transport leading to more
environmentally sustainable outcomes. Reduced car dependency and public transport
enhancements of the type discussed here may also be linked in an indirect way. For example:
(1) By including high occupancy vehicles in the bus priority treatment we may increase
average vehicle occupancy rates. However, the impact of a car being now potentially
available to other members of the household, may somewhat negate the overall impact
on vehicular travel;
(2) If the enhancement measures result in a reduction in road capacity, the long-term
outcome may be one of modal shifts away from car travel at congested times. However,
in the short term, there is a critical need to ensure that the loss in capacity and ensuing
increased congestion, coupled with a low initial usage made of the priority facility, is not
seen by motorists as ‘resource wasteful’. Therefore, a well thought out education and
information campaign is required. This apparent conflict between potential inefficient
use of road space in the short term and longer-term benefits, can be seen in assessment
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terms as effectiveness (in achieving modal shifts), versus efficiency in the use of
efficient road network capacity.
(3) The individual priority measure(s) when introduced in isolation, may have a limited
impact on reducing vehicle-induced congestion. However, they can be a powerful
reinforcing element of a package of measures which may include demand management
strategies (eg. parking pricing and supply, car pooling incentives and road pricing); and
public transport investment (eg. improved frequencies, bus fleet modernisation, new
ticketing system and new traveller information systems). By being directly visible to
motorists, the priority measures highlight the new distinguishing features between the
levels of service provided by the two modes.
Another set of issues arises when assessing network-wide impacts of bus priority measures.
The latter may have effects which go beyond impacts on general traffic on buses along the
arterial road under study. For example: if significant changes are induced to travel times for
general traffic, route choice effects may result in increases in vehicular travel for vehicles
using the main arterial, or for those experiencing increased delays at minor approaches to
intersections where buses are given priority. Temporal effects may accompany such spatial
impacts, such as changed peak period trip starting times, to avoid increased congestion.
The complexity of arterial road management issues necessitates an analysis of the impacts of
bus priority in the wider transport planning context. Nevertheless this approach does not
obviate the requirement for a micro-analysis of the bus priority treatments being
contemplated for a specific road link. Bus priority treatments are often used as a tool for
driving public transport efficiency rather than as a part of an overall transport strategy that
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considers the wider transport planning objectives and the local impacts of these measures.
This paper suggests an approach that considers all of these issues will result in more suitable
applications of bus priority treatments. In this regard, a methodology for identifying the
travel time benefits to buses and any associated impacts for the remainder of the traffic, is
identified in this work.
4. METHODOLOGY TO EVALUATE DIRECT TRAVEL TIME IMPACTS
4.1 Analysis Techniques
The analysis here examines the bus priority measures available and identifies conditions
where each of the treatments may be suitable. The effect on travel time for buses and general
traffic from bus priority measures was undertaken using a mix of analysis techniques. The
delay analysis tools used involved separate methodology for individual approaches,
signalised intersections and networks of signalised intersections. The focus of the
investigation was the passenger travel time and this was determined using computer
simulation and traffic flow analysis. The computer simulation was undertaken using SIDRA
version 4.5 and TRANSYT version 8. SIDRA is an intersection simulation package that was
used to obtain indicative delays and queues of individual signalised intersections. TRANSYT
is a traffic signal network analysis and is used to assess the impact of traffic signal
progression over a route. Whilst the computer packages allow a detailed analysis of various
conditions, a basic delay relationship was used to allow detailed analysis of individual
intersection approaches. The relationship adopted by Austroads (1991) to approximate the
total approach delay was considered appropriate for this work for Australian conditions. The
delay at an individual intersection is given by Equation (1). This relationship is used to
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determine the effects of average delay for an isolated intersection approach with uniform
traffic arrival patterns.
D=
qc (1-u)2 + n(o)x
..................................................(1)
2(1-y)
where:
D:
Total delay in vehicle-hours per hour
q:
flow in vehicles per second
c:
cycle time in seconds
u:
green time ratio = g / c
y:
flow ratio = q / s
n(o) :
the average overflow queue in vehicles.
An integral part of this work is the development of guidelines for suitable conditions where
the various bus priority measures may be justified. The break-even analysis is undertaken for
situations with and without bus priority treatments, to identify the minimum number of bus
passengers needed justify each treatment.
4.2 Evaluation of Bus Priority Treatments
The current analysis focuses on the impacts on overall journey time. Other impacts, such as
vehicle operating costs and environmental effects are not dealt with here. The base route
layout examined is shown in Figure 2. This is a typical 4-lane divided arterial road with
traffic signals at 250 metre spacing. Various bus priority treatments were considered for this
route to enable the conditions to be identified where these treatments are suitable.
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For each set of traffic conditions, the minimum number of bus passengers to justify a bus
priority treatment is given by:
Min.( bus) =
( dcar1 * Vcar * OCCcar) - ( dcar2 * Vcar * OCCcar) ……………………….(2)
___________________________________________
Vbus * (dbus2 - dbus1)
Where :Min (Bus)
= Minimum number of bus passengers to justify bus priority
dcar1
= Average delay to cars without bus priority
Vcar
= Volume of general purpose vehicles excluding buses
OCCcar
= Average occupancy of general purpose vehicles excluding buses
dbus1
= Average delay to buses without bus priority
Vbus
= Volume of buses
OCCbus
= Average number of passengers in buses
dbus2
= Average delay to buses with a bus priority
dcar2
= Average delay to cars with bus priority
Bus Lanes
The impacts of bus lanes on buses and the remainder of the traffic may be assessed by
considering the performance of the route with and without these lanes. The calculations are
based on an extra lane added to an approach designated either as a bus lane or as a general
purpose lane. It is assumed that an extra lane may be effectively used either as a bus lane or a
general purpose lane. Figure 3 shows the alternative options for adding extra lanes to the base
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case. The approach used here determines the total person delay for both options to identify
the lane arrangement that minimises this parameter. In some instances, the use of bus lane
‘set-backs’ may assist in maximising the benefits of the bus lanes. This is demonstrated in
Figure 3 with the bus lane set-back added to the base case. The method of investigating both
bus lanes extended through the intersection and where the bus lanes are set-back from the
stop line are considered separately.
Active Priority at Signals
The various strategies to be assessed could include dedicated bus phases, bus phase queue
jump, absolute bus priority, selective bus priority. Typical phasing associated with each of
these methods of priority are shown in Table 1. The use of active bus priority was modelled
using SIDRA to assess the effects of changing the traffic signal phase times. The average
vehicle delay was determined for the base case (no active signal priority) and for the case
where the signals are modified to give priority for buses. This assessment adopted random
arrivals of vehicles on the side street and random arrivals of buses.
4.3 Transit lanes on Arterial Roads
The person throughput may be analysed by comparing the operating conditions with a transit
lane and the case of the same lane being dedicated to general traffic. The analysis was
undertaken using equation (3). This approach allows the sensitivity of the results to be
assessed with the different conditions.
Min. number of =
( dNTV1 * VNTV * Cocc) - ( dNTV2 * VNTV * Cocc)
passengers in
_____________________________________
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....………...(3)
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transit lanes
(dTV2 - dTV1 )* VTV1
Where :dNTV1 = Average delay to cars without transit lane
VNTV = Volume of general purpose vehicles excluding transit vehicles
Ccar = Average occupancy of general purpose vehicles excluding transit vehicles
dNTV1 = Average delay to high occupancy vehicles without bus priority
VTV1 = Volume of vehicles eligible for transit lane
Tocc = Average number of people in high occupancy vehicles
dTV1 = Average delay to high occupancy vehicles with no transit lane
dTV2 = Average delay to vehicles in transit lane
5. SUMMARY RESULTS
This analysis investigated the various types of bus priority treatments and their suitability of
use in various situations using the methodology described in section 4. Jepson and Ferreira
(1998) provide detailed results from that work. The analysis focussed on a typical four lane
arterial route with signalised intersections at 250 metre spacing. The calculations were
undertaken on a detailed micro-analysis of specific road links. Table 4 summarises the
conditions for use of the various bus priority treatments. These results were compiled to
identify those locations where the various bus priority measures may be considered, and they
depict the minimum bus patronage required to consider each of these measures.
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The number of persons required to justify each treatment within the guidelines shown here,
would, in the first instance, be based on actual passenger numbers. However, it is
acknowledged that the bus priority treatment may be part of an overall strategy to increase
the patronage of buses. Using marketing tools such as advertising, improving comfort levels
and fare re-structuring, coupled with the bus priority treatment, there may be a significant
increase in patronage for buses. In these circumstances, the appropriate bus priority treatment
may be analysed using the predicted traffic conditions and bus patronage levels.
6. SUMMARY AND CONCLUSIONS
There have been a variety of bus priority systems used for at least 25 years in various areas
throughout the world. European countries, particularly England, have pioneered many of the
bus priority systems on arterial streets. Many of the systems associated with freeway
operations have been developed United States of America. Bus lanes and traffic signal
priority are the most common forms of bus priority and these systems provide significant
travel time savings in congested arterial roads. Table 2 shows the treatments to improve bus
priority that were reviewed here. Table 3 summarises the applications of the treatments under
study.
The results shown in Table 4 give ‘ball - park’ indications of operating conditions needed to
justify each priority treatment. It is acknowledged however, when assessing the need for bus
priority treatments, a detailed investigation of each route needs to be undertaken. Thus these
results may be used as a filter type mechanism to assist in identifying the selection of bus
- 21 -
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priority treatments for particular locations. Whilst these results may assist in assessing bus
priority treatments, they should only be used as a guide.
The above analysis does not take into account a number of factors. The inclusion of car and
bus operating costs reduces the minimum number of buses required due to the higher relative
operating costs of buses. The environmental savings will also have an effect on this analysis.
In addition, the desirability to promote buses to improve the overall efficiency of the
transport network provides benefits in favour of this form of public transport.
This work serves to highlight the issues involved in the assessment of bus priority treatments.
The selection of these treatments must be consistent with the traffic management strategy for
a route. As the traffic management strategy is linked to the transportation demand and supply
issues in an urban area, bus priority should be assessed as part of an overall management
approach. The route layout and hierarchy, land use planning, availability and integration of
alternative transportation modes are some of the issues that would influence a transport
strategy. Furthermore, bus priority may provide substantial savings to bus journey times and
if correctly located will have a manageable impact on the general purpose traffic. This paper
suggests that bus priority treatments should be treated in this manner rather than as a panacea
to solve all congestion problems on urban arterials
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LIST OF TABLES AND FIGURES
Table 1. Strategies For Active Bus Priority At Traffic Signals
Table 2. Summary of Bus Priority Treatments Reviewed
Table 3. Summary of Guidelines for Use of Bus Priority Treatments
Table 4: Summary of Justification for Bus Priority Treatments
Figure 1. Assessment of Bus Operating Enhancements
Figure 2 : Base Route Layout for Analysis of Bus Priority Treatments
Figure 3. Bus Lane Extended Through Intersection and Extra Lane Designated for
General Purpose
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Table 1. Strategies For Active Bus Priority At Traffic Signals
Bus Arrival Period
Bus Phase
Bus arrives during green
phase of intersection.
No change
in phasing
Bus
Phase
Queue Jump
No change in
phasing.
Absolute Bus Priority
Selective Bus Priority
No change in phasing.
No change in phasing.
Bus arrives 0 to 13
seconds from the end of
the green phase.
Phasing is
modified to
provide a
green light
for bus
Bus receives
a 5 s green
phase prior to
start of next
green
Extend green phase to
accommodate the bus.
Extend green phase to
accommodate the bus.
Bus arrives between 13
seconds from the end of
the green phase and 13
seconds from the start of
the next green phase.
Phasing is
modified to
provide a
green light
for bus
Bus receives
a 5 s green
phase prior to
start of next
green
Cut off opposing green
phase and return the
green phase for the
approach with the bus
arriving.
The
modifications to the
opposing phases must be
made with a minimum
green time of 6 seconds.
Cut off opposing green
phase and return the
green phase for the
approach with the bus
arriving 13 seconds
early. A bus that arrives
during the red phase will
have to wait until the
start of the next green
phase.
Bus arrives 0 to 13
seconds from the start of
the green phase for the
approach the bus is
travelling.
Phasing is
modified to
provide a
green light
for bus
Bus receives
a 5 s green
phase prior to
start of next
green
Cut-off the green phase
for opposing approaches
and start the green phase
for the bus approach
early by the required
time to allow the bus to
receive a green light.
Cut-off the green phase
for opposing approaches
and start the green phase
for the bus approach
early by the required
time to allow the bus to
receive a green light.
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Table 2. Summary of Bus Priority Treatments Reviewed
Arterial Road Treatment
Description
Treatments to Address Bus Travel Time
General Arterial Road M’ment
‘With-flow’ bus lanes
Median bus lanes
Bus streets / bus malls
Bus Lane Set-Back
Active Priority for Buses at Signals
Passive Priority at Traffic Signals
Adjustment of Signal Phasing
or area-wide timing plans
Gating (Metering Vehicles)
Turn prohibition
Transit lanes on Arterial Roads
Transit Facilities on Freeways
Busways
Bus Priority to Access Freeways
Measures To Provide Priority by
Investigation of Bus Stops
Bus Stop Relocation
Increase Bus Stop Spacing
Create Lay-bys.
Addressing Delays due to Passengers
Boarding and Alighting
Reduce time Spent at Bus Stops
Bus Convoys
Examination of techniques for improving travel time for
buses and general traffic (ie. review of signal spacing, median
break policy etc.)
Extensively used throughout the world by redesignating a
kerb-side lane for buses during peak hours.
Locations with line-haul bus routes and restricted right turns.
High numbers of buses and passengers (ie. CBD area).
Widespread use in the UK. Set-back of bus lane from signals
to maintain capacity of intersection.
Selective detection and priority to buses is used throughout
the world. Developments in technology has renewed interest.
Design signals to suit requirements of bus routes. This is a
common approach that may produce modest improvements.
This technique meters flow into an area to reduce the
congestion over a section of an arterial road. Several
examples in the UK. May allow buses priority around
congested areas without unduly changing operations for cars.
If turning vehicles cause congestion, the banning of particular
movements will reduce congestion and favour bus operations.
May be used in lieu of bus lanes where bus numbers are low
to encourage use of car-pooling.
Encourages car-pooling on freeways. Common in the USA
and provide high level of service for buses and HOVs into
and out of the CBD on the freeway system. May be barrier
separated or have flows concurrent with general traffic.
Busways are a premium facility providing a separate right of
way for buses. Several examples are located throughout
world.
Systems to improve bus or hov access to the freeway using
either queue bypass of ramp metering or exclusive ramps.
Consider most appropriate site for individual bus stops.
Consider most appropriate spacing for bus stops.
Indented bays to separate stationary buses from traffic stream.
Using improved information or ticketing to improve the
boarding time of buses.
Used in several locations to facilitate bus loading
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Table 3. Summary of Guidelines for Use of Bus Priority Treatments
Bus Priority Treatment
Bus Lanes
‘With-flow’ bus lanes
Typical Guidelines for Use
Key References
General Guidelines : Often used for peak hours only.
Moderate - high bus numbers
United Kingdom :
Used warrants that depend on the level of congestion and
numbers of buses such as:
Congestion(D.of S.)
Minumum No.Buses
0.7
65/hr
0.8
60/hr
0.9
50/hr
0.95
20/hr
0.97
5/hr
Recently have assessed bus lanes using simulation models as
part of larger schemes.
United States :
Use criteria of number of buses/hour and passengers/hour.
Minumum 30 - 40 buses & 1200 passengers / hour.
Australia :
Use criteria developed in the United States to maximise person
throughput which equates to the equation as shown :
Min. Bus Flow = No. of cars x ratio of car & bus occupancy
Total number of lanes - 1
Median bus lanes
General guidelines : High numbers of buses
Line - haul bus routes
Limited right turns
United States :
Minimum bus flow : 60 -90 /hr. & 2400 - 3600 passengers/hr.
& ability to separate turning traffic from buses.
Australian Applications :
Sydney Harbour Bridge : 165 buses /hr (7000 passengers)
Bus streets / bus malls
General guidelines : High numbers of buses & passengers
Applicable for CBD areas
Bus Lane Set-Back
General guidelines : Bus lane ends a set distance from traffic
signals to retain capacity of intersection.
United Kingdom :
Depends on congestion & bus numbers. Optimum set-back 2.5
m/s at 95 % of saturation & 1 m/s at 70 % of saturation.
Congestion
(Deg. of Sat.)
0.7
0.8
0.9
0.95
0.97
Minumum No.Buses
(Optimum Setback)
65/hr
60/hr
50/hr
20/hr
5/hr
Priority to Buses at Signals
- 37 -
Minimum No. Buses
(No Set-back)
105/hr
120/hr
120/hr
100/hr
85/hr
Oldfield,R.H.
(1978)
Bly, P.H. (1978)
Robertson, G.D.
(1985)
Transportation
Research Board
(1994)
Taylor, M.A.P.
(1996)
Vuchic, V.R. (1981)
Levinson, H.S.
(1987)
Quail, D.J. & West,
R.P. (1987)
Oldfield, R.H
(1977)
Bly, P.H. (1978)
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Active Priority for Buses
Passive Priority at Traffic
Signals
Adjustment of Signal
Phasing or area-wide
timing plans
Gating (Metering
Vehicles)
Turn prohibition
Transit lane on Arterial
Roads
Transit Facilities on
Freeways
Busways
General Guidelines : Assessed on the basis of benefits vs
costs.
No typical guidelines developed yet.
Various cities are using bus priority as
part of traffic management scheme.
Significant Users
United Kingdom : Selknet, Leeds
Europe : Turin, Golthenburg, Stuttgart
United States :Minneapolis, Portland
Australia : Brisbane
General Guidelines : Assesses priority based on weighting
of buses (1 bus = 10 - 20 cars)
No warrants for implementation available.
General Guidelines : Used to relocate queues to the benefit of
a bus route.
Significant Example : Uxbridge Road (West London)
General Guidelines : Used to improve capacity without
affecting bus operations.
General Guidelines : Improve capacity of arterial by
increasing the person throughput
General Guidelines : Improve capacity of arterial by
increasing the person throughput.
Effective if has min. travel time saving
of 1 min./mile & total saving of 7 mins.
Capacity should be less than 1000 vehs/hr
General Guidelines : Carriageway dedicated for buses
Requires large numbers of buses to justify
Significant Examples : Pittsburg
Ottawa
General Guidelines : Enhances buses entry to freeways
Bus Priority to Access
Freeways
- 38 -
Hounsell, N.B.
Holzworth,
Fox,
Batz, T.M. (1986)
Kloos, (1994)
Boje, (1996)
Miorandi, J. &
Campbell, J. (1997)
Oakes, J. (1995)
Turnbull, KF
(1992b)
Transportation Res.
Board (1994)
Nurworsoo,C.K.
(1988)
Hardy, T.C. (1987)
Bonsall, J.A. (1987)
Batz, T.M. (1986a)
11/11/20052491.doc
Table 4: Summary of Justification for Bus Priority Treatments
Bus Lane Treatments
Main
Approach
Volume
(veh/h)
2000
2000
2000
2000
1500
1500
1500
1500
1000
1000
1000
1000
Active Bus Priority at traffic signals
Minor
Bus Lane Bus Lane Dedicated Queue
Approach Extended set - back
Bus
Jump
Volume to stop line from stop
Phase Bus Phase
(veh/h)
(1)
(1)
(1)
(1)
100
300
500
700
100
300
500
700
100
300
500
700
Notes : (1)
(2)
(3)
(4)
(5)
n/a
n/a
n/a
n/a
1550
1550
1550
1550
850
850
850
850
100
100
100
100
100
100
100
100
100
100
100
100
>10000
>10000
>10000
>10000
1755
1901
3006
>10000
860
1040
2400
>10000
60
240
1600
>10000
49
195
1300
>10000
14
57
378
>10000
Absolute
Bus
Priority
(1)
100
100
1539
4479
100
100
>10000
>10000
100
285
>10000
>10000
Selected
Bus
Priority
(1)
100
100
100
2334
100
100
>10000
>10000
100
100
4014
>10000
Passive priority at traffic signals
Design of
Restriction
signals for bus of right turn
travel time
buses
of 30 km/h
excepted
(1)
(1)
2500
(2)
2500
(2)
2500
(2)
2500
(2)
1900
(5)
1900
(5)
1900
(5)
1900
(5)
1400
(5)
1400
(5)
1400
(5)
1400
(5)
This column depicts the minimum number of bus passengers/hour required for each of the
bus priority treatments to be justified to maximise the person throughput.
This indicates that this form of bus priority may be considered further for this situation.
This column depicts the minimum number of passengers / hour eligible for the transit lane
to maximise the person throughput.
This indicates the analysis was not undertaken for this situation
This indicates that this form of bus priority is not appropriate for these traffic conditions
- 39 -
Metering
of flows
Transit
Lane
(1)
(2)
(2)
(2)
(2)
(5)
(5)
(5)
(5)
(5)
(5)
(5)
(5)
(3)
2000
2000
2000
2000
1300
1300
1300
1300
(4)
(4)
(4)
(4)
Improve
d
Busways Ticketing
Bus Stop
location
review
(1)
(1)
(2)
(2)
(2)
(2)
(2)
(2)
(2)
(2)
(5)
(2)
(5)
(2)
(5)
(2)
(5)
(2)
(5)
(2)
(5)
(2)
(5)
(2)
(5)
(2)
11/11/052491.doc
Figure 1. Assessment of Bus Operating Enhancements
Network Performance
Operational
Direct Impacts
Economic
Environmental
Indirect Impacts
Bus travel times
Modal shifts
Bus operating costs
Route choice
Car travel times
Car operating costs
Trip start times
Emissions
Car pooling
Energy consumption
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Side Street
Side Street
Side Street
Figure 2 : Base Route Layout for Analysis of Bus Priority Treatments
Main Arterial
Main Arterial
250 metres
250 metres
Base Case : Route for Analysis
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Bus lane set - back
from stop line
Bus lane
Bus lane
Bus lane
Bus lane
Bus lane
Side Street
Main Arterial
Side Street
Side Street
Figure 3. Bus Lane Extended Through Intersection and Extra Lane Designated for General
Purpose
Option A
Bus lane
Bus lane
Bus lane
Main Arterial
250 metres
250 metres
Base case with bus lane set-back
from intersection
Bus lane
Side Street
Main Arterial
Side Street
Side Street
Option B
Bus lane
Bus lane
Bus lane
Main Arterial
250 metres
250 metres
Base case with bus lane extended
through intersection
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