Keywords: microscopic simulation, traffic signals, estimating delays, semi-actuated control, stochastic systems, queuing systems.

Traffic signals operating with semi-actuated control [3] have been widely used on secondary streets, since they provide flexible controls adjustable by traffic volumes, reducing vehicle delay. The literature offers very few methods for dealing exclusively with semi-actuated signals in estimating delays. A common approach is to estimate average green times and average cycle lengths [1] and then apply a model for pre-timed signals to estimate delays [2]. The efficient use of semi-actuated control requires careful selection of phasing plan, timing design and detector configuration. Computer simulation can be used to help the engineer in the search for the optimal timing plan. The main problem when using semi-actuated control is the difficulty of selecting the best combination of maximum green time, minimum green time and unit extension of green time.

In this research, a microscopic simulation program has been used for evaluating operating conditions and for estimating vehicular delay at an isolated intersection with semi-actuated control signals [5]. The total delay is defined, in this program, as the difference in travel time between when a vehicle is affected by controlled intersection and when a vehicle is unaffected by the controlled intersection [4]. The delays associated with different regulation plans are characterized.

In this study, we used an intersection with signals, located in the Porto metropolitan area, that is operated with semi-actuated control. The intersection is between one secondary street, with an actuated control signal, and a main street with no actuated control. We assume that there is a sensor in the secondary street, located a few metres from the stop line. Relative to the signal timing two phases are considered, one for the vehicles that cross the main street and another one for the vehicles that circulate in the secondary street. Probabilistic distributions were used to characterize vehicles (desired speed, maximum acceleration and distance headways) and their random arrivals. Hourly traffic flow rates vary from 100 to 700 veh/h in the actuated street and are between 700 and 800 veh/h in the main street. We analyse the influence of the unit extension and the maximum green time in the total vehicular delay of the intersection and determine the best combination of values for these two parameters. We conclude that, for the intersection under study, the best timing plan includes a unit extension of 4 seconds and the maximum green time must be set equal to 40 seconds.

1

R. Akcelik, "Estimation of green times and cycle time for vehicle-actuated signals", Transportation Research Record, 1457, 398-417, 1994.

2

N.M. Rouphail, M. Anwar, D.B. Fambro, P. Sloup, C.E. Perez, "Validation of generalized delay model for vehicle-actuated traffic signals", Transportation Research Record, 1572, 105-111, 1997. doi:10.3141/1572-13

3

F.-B. Lin, "Knowledge base on semi-actuated traffic-signal control", Journal of Transportation Engineering, 117(4), 398-417, 1991. doi:10.1061/(ASCE)0733-947X(1991)117:4(398)

4

C. Quiroga, D. Bullock, "Measuring control delay at signalized intersections", Journal of Transportation Engineering, 125(4), 271-280, 1999. doi:10.1061/(ASCE)0733-947X(1999)125:4(271)

5

M.L. Simões, A.P. Costa, P.M. Oliveira, "Simulation and modelling of traffic movements at semi-actuated signalised intersections", in CUPUM07, 2007.

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