N.B. Hounsell

Bus priority using pre-signals

The need to provide efficient public transport services in urban areas has led to the implementation of bus priority measures in many congested cities. Much interest has recently centred on priority at signal controlled junctions, including the concept of pre-signals, where traffic signals are installed at or near the end of a with-flow bus lane to provide buses with priority access to the downstream junction. Although a number of pre-signals have now been installed in the U.K., particularly in London, there has been very little published research into their design, operation and optimisation. This paper addresses these points through the development of analytical procedures which allow pre-implementation evaluation of specific categories of pre-signals. The paper initially sets out three categories of pre-signal, which have different operating characteristics, different requirements for signalling and different impacts on capacity and delay. Key issues concerning signalling arrangements for these categories are then discussed, together with a summary of the analytical approach adopted and the assumptions required. Equations are developed to allow appropriate signal timings to be calculated for pre-signalised intersections. Further equations are then developed to enable delays to priority and non-priority traffic, with and without pre-signals, to be estimated with delay being taken here as the key performance criterion. The paper concludes with three application examples illustrating how the equations are applied and the impacts of pre-signals in different situations.The analyses confirm the potential benefits of pre-signals, where these signals apply to non-priority traffic only. Where buses are also subject to a pre-signal, it is shown that disbenefits to buses can often occur, unless bus detectors are used to gain priority signalling.

Quantifying the potential savings in travel time resulting from parking guidance systems - a simulation case study

Parking Guidance and Information (PGI) signs are thought to enable a more efficient use of the available parking stock. Despite the installation of PGI systems in many cities and their operation for a number of years, there is a lack of reliable evidence of the size of the benefits that these systems can achieve. This paper describes the development of driver parking choice models (both during the journey and pre-trip) and the implementation of these models in the existing network traffic simulation model RGCONTRAM. Besides quantifying the effects of the PGI system on both the drivers seeking suitable parking spaces and the parking stock itself, this also enables quantification of the impact of parking choice on the wider network. Factors influencing PGI effectiveness are described and conclusions are drawn that illustrate the potential of PGI to induce the demand to spread more efficiently across the parking stock.

A New Approach for Co-Operative Bus Priority at Traffic Signals

Bus priority at traffic signals is a growing area of cooperative transport system applications. Interest in bus priority continues to grow as the cities pay more attention to the needs of buses to provide fast, frequent, and reliable services, thus contributing to a sustainable transport system. Bus priority at traffic signals is particularly favored at places where road space is limited and traffic signal density is high. With increasing the use of automatic vehicle location (AVL) systems, it is now possible to provide “differential” priority, where different levels of priority can be awarded to buses at traffic signals according to chosen criteria (e.g., to improve regularity). At present, common strategies are based on the comparison of the time headway of a bus with the scheduled headway. However, this paper shows that greater regularity benefits could be achieved through a strategy where priority for a bus is based not only on its own headway but also the headway of the bus behind (the following bus). This paper demonstrates the benefits of this on a theoretical basis and quantifies the benefits from simulation modeling of a high-frequency bus route. Such a strategy provides an opportunity to exploit the more detailed location information available from the growing number of AVL-based systems for buses being implemented around the world.

PASSENGER CAR UNITS IN SATURATION FLOWS: CONCEPT, DEFINITION, DERIVATION

Passenger car units (pcus) are traditionally used to represent the effects of changes in traffic composition (the mix of cars, goods vehicles, buses, ad so on) on the saturation flows at traffic signal junctions. This paper describes in the results obtained by the two main methods of derivation of pcu values, regression analysis of asynchronous vehicles counts (asynchronous regression) and headway ratio methods, when applied to data from two large public road studies. The relationship between the various methods of derivation used is investigated. Regression analysis of synchronous vehicle counts, Websters method, and headway ratio methods are seen to agree, but asynchronous regression necessarily gives lower results so long as there is variability in the headways of vehicles of a given class (e.g. in car-to-car headways). Alternative method of regression analysis of asynchronous counts is investigated but found to be biased, although les so than the existing method. Conventional asynchronous regression gives unbiased saturation flow estimates if unbiased prior pcu values are used. The effects of assumed pcu values on signal settings and consequent delays in subsaturation conditions are examined. Value corresponding to delay-minimising settings are close to the ratio of the mean headways of the appropriate vehicle classes.

Strategies for route guidance systems taking account of driver response

Continuing research and development into new technologies for road transport systems is leading to the evolution of a wide range of dynamic route guidance (DRG) and driver information systems. These range from out-of-vehicle roadside displays providing variable message/direction signs, to in-vehicle systems, such as navigational aids, map-based systems, audible systems (e.g. radio) and fully dynamic route guidance systems advising appropriate turns at each junction encountered. This high level of system development has been matched with considerable scientific activity in system design and evaluation using offline modelling tools. For DRG systems, the challenging tasks for the models have been to realistically capture the dynamic effects of traffic and of the DRG systems, and the driver responses to each. This paper describes the development of a model RGCONTRAM designed specifically to address these issues so that efficient operational strategies for route guidance systems can be identified.

Role of the Travel Factor Convenience in Rail Travel and a Framework for its Assessment

Abstract This paper reviews the travel factor convenience with particular regard to rail travel. Past research has shown that convenience is a concept readily associated with the private car and its perceived ability to provide a door‐to‐door journey. Private vehicles such as cars are often key competitors to public transport. However, convenience with regard to public transport has proved to be somewhat of an ambiguous concept, often showing a high degree of overlap with the other main recognized travel factors. This paper shows that it is possible to consider convenience in rail travel as an embodiment of four themes: access/egress, station facilities/environment, frequency of service/scheduling and interchange between train services. A list of physically measurable elements can be produced relating to these four themes in order to assess the convenience of any particular station. A categorization process is proposed based upon the initial findings of a questionnaire designed to obtain a user perspective upon convenience. It is concluded that no definitive measure of convenience can be produced for rail travel, although a proxy measure, based upon categorization, containing some or all of the defined elements should be possible.

Modelling The Dynamics Of Route Guidance

This paper concentrates on simulation modelling aimed at studying the relative benefits of the dynamic elements of route guidance systems within the two DRIVE projects CARGOES and LLAMD.

Urban network traffic control

Abstract The optimum control of traffic in urban networks is an important requirement of city authorities as they seek efficient and sustainable transport. A feature of most urban networks is the high density of city streets with numerous road junctions, which require efficient control mechanisms if congestion is to be contained. Traffic signals have become the most widely used form of control in this context, with increasing sophistication in detection and real-time optimization providing new levels of efficiency. A changing policy background in many cities has also required greater emphasis in traffic control on the needs of public transport, cyclists and pedestrians, and on the need to minimize vehicle emissions. This paper provides an overview of problems, methods, systems and applications in the context of urban network traffic control, concluding with a look at future needs. The paper focuses particularly on signallized junctions within computer-controlled urban traffic control (UTC) systems, which are increasingly at the heart of traffic control in cities around the world.

Bus Priority at Traffic Signals—Evaluating Strategy Options

This article compares different strategy options for providing bus priority at traffic signals. The different strategies considered vary in the strength of the priority awarded and in the selection of the buses that are to receive priority. The strategies include so-called differential priority, where buses receive individual priority treatment according to some criterion such as lateness, and nondifferential priority, where all buses are treated in the same way. The strategies are compared using a simulation model, SPLIT, that has been developed and validated. The article describes some of the modelling issues that are involved in simulating bus priority systems and how they have been treated with the SPLIT model.

AUTOMATIC VEHICLE LOCATION: IMPLEMENTATION, APPLICATION, AND BENEFITS IN THE UNITED KINGDOM

Automatic vehicle location (AVL) is playing an increasingly important role in public transport operations in the United Kingdom, providing support for real-time management and control of bus fleets and the platform for other beneficial functions including passenger information systems and bus priority. The current and emerging use of AVL in the United Kingdom for public transport is considered in this paper, focusing in particular on developments in London and Southampton where substantial use is being made of AVL. Following a summary description of AVL systems and technologies, examples are presented of the use of AVL for real-time passenger information at bus stops, particularly the COUNTDOWN and STOPWATCH systems in London and Southampton, respectively. Technical aspects are described together with evaluation results including passenger attitudes and financial criteria. Positive results in both cities have led to commitments for citywide implementations. The use of AVL in applications for bus priority at traffic signals is described, including a comparative review of different architectures and techniques that have emerged. Results of a feasibility study for the use of AVL in this context in London are presented. This study indicated that using AVL to target high-occupancy, high-headway buses with higher levels of priority could provide economic benefits for buses and passengers up to twice those achieved with current operations, where priority is equally available to all buses. Deployment details of this application, related to COUNTDOWN, are described. The paper concludes with the outlook for AVL, particularly for greater integration with traffic control systems, where significant potential benefits are outlined.