On-ramp metering based on three-phase traffic theory - Part Ⅲ

摘要

In this part Ⅲ of the article, a congested pattern control approach (ANCONA) introduced by the author in 2004 is discussed. The ANCONA approach, which is based on the author's three-phase traffic theory, should address the drawbacks of other on-ramp metering strategies based on a free flow control approach in which free flow should be maintained at an on-ramp bottleneck (parts Ⅰ and Ⅱ of the article). These drawbacks are associated with the probabilistic nature of traffic breakdown: regardless of free flow control application, traffic breakdown can nevertheless occur at the bottleneck. In contrast with the free flow control approach to feedback on-ramp metering, ANCONA does not restrict on-ramp inflow as long as free flow is measured at the bottleneck. ANCONA begins to perform only after traffic breakdown occurs at the bottleneck, ie, ANCONA allows congestion at the bottleneck to set in. The basic idea of ANCONA is to keep traffic congestion at the minimum possible level at the bottleneck: (ⅰ) through the use of ANCONA, average speed within a congested pattern should be maintained at relatively high level (higher than about 60 km/h) and; (ⅱ) the congested pattern should be localised on the main road in the near neighbourhood of the bottleneck. To reach these goals, after traffic breakdown has occurred spontaneously at the bottleneck, ANCONA tries to return to free flow at the bottleneck. A critical comparison of ANCONA with ALINEA and UP-ALINEA is made.