Maximizing throughput by providing unidirectional and broken coordination on oversaturated arterials at actuated signal controlled intersections

Abstract

The major problems associated with the operation of oversaturated arterials are unpredictable growth of queues, and inability of existing software packages like PASSER II to provide satisfactory timing plans during periods of congestion. The primary objective of this research was to determine strategies that could better deal with oversaturated arterials. The following four strategies were evaluated: 1.Simple one-way progression in the congested direction (Strategy 1) 2.Simple one-way progression in the uncongested direction (Strategy III) 3.Two-way progression in the arterial with the critical intersection isolated (Strategy III) 4.Continuous progression band in the uncongested direction and broken progression band at the critical intersection in the congested direction (Strategy M. Simulation studies were performed using TRAF-NETSIN4 software package to evaluate and compare the effectiveness of the four strategies with the direct implementation of PASSER-II timings (Base Strategy). A hypothetical arterial of five intersections operating in coordinated actuated mode with a cycle length of 140 seconds was simulated. The third intersection was the critical intersection and only through traffic movements were considered. The measures of effectiveness (MOE) were 1) total system delay, 2) average system delay, 3) throughput of the arterial in both the directions, 4) phase failures at the intersections, and 5) queue lengths in the various links. Two new experimental MOES, the number of stops selected vehicles made in going through the arterial and the total stops at each intersection, were also used. Two operational regions were identified in this research. It was found that none of the strategies provided significant improvement over the others for the first operational region encompassing a range of D/C ratios between 0.86 and 1.00. Strategy I produced much better arterial operation for the second operational region encompassing the range of D/C ratios between 1.06 and 1.21. It was suggested by the author that arterials experiencing increasing levels of congestion be operated in the PASSER II strategy until a D/C ratio of 0.86. Beyond which the arterial should be operated according to simple one-way progression in the congested direction strategy (Strategy I).