摘要: |
The current emphasis on utilizing existing transportation infrastructure more efficiently has added impetus to the recent focus on advanced traffic management systems. An advanced traffic management system typically combines existing hardware, software, and traffic engineering expertise to observe and manage transportation systems more effectively. The potential of ramp metering to provide reductions in system delay has been recognized for some time. Simple analytical techniques have been used to demonstrate the magnitude of these benefits. However, these analytical methods can rarely reflect fully all the spatial and temporal dynamics that may exist within integrated freeway and arterial networks. In this paper a network traffic simulation model is used to examine the potential benefits of implementing ramp metering strategies and to quantify how sensitive these benefits are to a number of factors including the metering rate, the timing of the implementation of the metering, and various assumptions regarding driver rerouting behavior. The results of this investigation indicate that, as expected, ramp metering can result in reductions in total travel time, but it may also yield increased net delays if it is not implemented correctly. This investigation indicated that the temporal window of opportunity during which ramp metering can be implemented and be of benefit is surprisingly small. Results for a simple network indicate that under ideal conditions, in which drivers are able to divert their routes, a benefit of as much as a 14% reduction in total travel time may be possible. If it is assumed that a capacity loss of 5% occurs once the freeway becomes congested, then the benefit of metering may be as great as a 26% reduction in total travel time. |