22-01-2013, 11:13 AM
Role of variable speed limits, ramp metering and hard shoulder running in motorway management
ABSTRACT
The provision of ITS equipment for management of motorways has become commonplace throughout Europe. Installations typically comprise measures to manage mainline traffic streams in an attempt to avoid flow breakdown, with additional measures to enhance capacity or restrict excessive traffic volumes from joining the mainline under congested or near-congested conditions.
Over the past 15 years, a general consensus has emerged regarding the role and function of function of Ramp Metering and Access Control on motorways, and has supported the deployment of numerous systems throughout the world. Likewise, the benefits of Hard Shoulder Running can be
easily established. For Variable Speed Limits, the discussion is somewhat less certain. US deployments have focused on objectives to improve safety, whereas UK systems have a stated objective to improve capacity as well as safety. A research review highlights evidence to suggest that it can be extremely difficult to generate journey time benefits from a VSL system, and as such key benefits will comprise safety improvements resulting from a general reduction in stop-start driving. This assertion is borne out by results of the evaluation of the M25 in London, which highlighted quite limited journey time benefits but a notable safety improvement.
This evidence seems to contradict the general consensus that reducing the incidence of flow breakdown can protect carrying capacity of a motorway, given that flow breakdown itself can reduce carrying capacity locally by up to 15%. As such, removing such occurrences is key to avoiding the onset of such bottlenecks. In other words if avoiding flow breakdown through VSL installations is theoretically sound, why have such benefits not been observed in practice.
The current paper examines the impact of VSL, Ramp Metering and Hard Shoulder Running as individual strategies, and progresses to understand how they interact with each other. The paper uses Microsimulation techniques to understand vehicle behaviour in various environments, and the impact of various combinations of strategies. Nevertheless, the objective here is not to understand the preferred strategy for a particular situation, but instead to understand why such responses are occurring. This informs a general understanding of the function of the different systems, and how they influence the flow of the traffic stream.
ABSTRACT
The provision of ITS equipment for management of motorways has become commonplace throughout Europe. Installations typically comprise measures to manage mainline traffic streams in an attempt to avoid flow breakdown, with additional measures to enhance capacity or restrict excessive traffic volumes from joining the mainline under congested or near-congested conditions.
Over the past 15 years, a general consensus has emerged regarding the role and function of function of Ramp Metering and Access Control on motorways, and has supported the deployment of numerous systems throughout the world. Likewise, the benefits of Hard Shoulder Running can be
easily established. For Variable Speed Limits, the discussion is somewhat less certain. US deployments have focused on objectives to improve safety, whereas UK systems have a stated objective to improve capacity as well as safety. A research review highlights evidence to suggest that it can be extremely difficult to generate journey time benefits from a VSL system, and as such key benefits will comprise safety improvements resulting from a general reduction in stop-start driving. This assertion is borne out by results of the evaluation of the M25 in London, which highlighted quite limited journey time benefits but a notable safety improvement.
This evidence seems to contradict the general consensus that reducing the incidence of flow breakdown can protect carrying capacity of a motorway, given that flow breakdown itself can reduce carrying capacity locally by up to 15%. As such, removing such occurrences is key to avoiding the onset of such bottlenecks. In other words if avoiding flow breakdown through VSL installations is theoretically sound, why have such benefits not been observed in practice.
The current paper examines the impact of VSL, Ramp Metering and Hard Shoulder Running as individual strategies, and progresses to understand how they interact with each other. The paper uses Microsimulation techniques to understand vehicle behaviour in various environments, and the impact of various combinations of strategies. Nevertheless, the objective here is not to understand the preferred strategy for a particular situation, but instead to understand why such responses are occurring. This informs a general understanding of the function of the different systems, and how they influence the flow of the traffic stream.