Optimized Policies for Adaptive Control (OPAC)
The second-GC and third-GC strategies were expected to perform better than the
first-GC strategy, as they seemed to provide better responsiveness to traffic conditions
by using detected and predicted dada. However, some field tests showed that the
first-GC strategy in general outperformed the other two strategies (35,39,40). Due to the
unsatisfactory results of the second-GC and third-GC strategies (35,39,40), Gartner (35)
suggested a truly demand-responsive control strategy that is not restricted to the
conventional concepts of cycle length and phase durations (8).
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In his research, Gartner first presented an isolated intersection traffic control
example using a dynamic programming approach, later named as OPAC-1 (41), that was
similar to DYPIC (29). Gartner discussed that though this dynamic programming
approach can guarantee global optimality, it is not suitable for real time applications due
to the excessive computation time and the requirement of exact traffic arrival data.
Based on OPAC-1, Gartner proposed a simplified control algorithm using Optimal
Sequential Constrained Search (OSCS) algorithm instead of dynamic programming (8).
The resulted new control method was referred to as OPAC-2. The OSCS algorithm
requires less computation time but can produce results that are close to the optimal ones
produced by the dynamic programming approach. However, the OSCS algorithm is less
straightforward compared with the dynamic programming approach. To implement the
OSCS algorithm, there are three steps to follow
Optimized Policies for Adaptive Control (OPAC)The second-GC and third-GC strategies were expected to perform better than thefirst-GC strategy, as they seemed to provide better responsiveness to traffic conditionsby using detected and predicted dada. However, some field tests showed that thefirst-GC strategy in general outperformed the other two strategies (35,39,40). Due to theunsatisfactory results of the second-GC and third-GC strategies (35,39,40), Gartner (35)suggested a truly demand-responsive control strategy that is not restricted to theconventional concepts of cycle length and phase durations (8).20In his research, Gartner first presented an isolated intersection traffic controlexample using a dynamic programming approach, later named as OPAC-1 (41), that wassimilar to DYPIC (29). Gartner discussed that though this dynamic programmingapproach can guarantee global optimality, it is not suitable for real time applications dueto the excessive computation time and the requirement of exact traffic arrival data.Based on OPAC-1, Gartner proposed a simplified control algorithm using OptimalSequential Constrained Search (OSCS) algorithm instead of dynamic programming (8).The resulted new control method was referred to as OPAC-2. The OSCS algorithmrequires less computation time but can produce results that are close to the optimal onesproduced by the dynamic programming approach. However, the OSCS algorithm is lessstraightforward compared with the dynamic programming approach. To implement theOSCS algorithm, there are three steps to follow
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