• Journal of Korean Society of Transportation
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• v.19 no.3
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• pp.101-113
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• 2001

Since late 1970s. one of the principal research areas in transportation problem is dynamic traffic assignment (DTA). Although many models have been developed regarding DTA, yet they have some limits of describing real traffic patterns. This reason comes from the fact that DTA model has the time varying constraints such as state equation, flow propagation constraint, first in first out(FIFO) rule and queuing evolution. Thus, DTA model should be designed to satisfy these constraints as well as dynamic route choice condition, dynamic user equilibrium. In this respect, link-based DTA models have difficulty in satisfying such constraints because they have to satisfy the constraints for each link, while path-based DTA models may easily satisfy them. In this paper we develop a path-based DTA model. The model includes point queue theory to describe the queue evolution and simulation loading method for depicting traffic patterns in more detail. From a numerical test, the model shows promising results.

• Journal of Korean Society of Transportation
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• v.33 no.5
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• pp.478-487
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• 2015

This study proposed a Variable Speed Limits(VSL) algorithm to use traffic information based on Cumulative Demand-Capacity Analysis and evaluated its performance. According to the analysis result, the total of delay consisted of 3 separate parts. There was no change in total travel time although the total of delay decreased. These effects was analysed theoretically and then, evaluated through VISSIM, a microscopic simulator. VISSIM simulation results show almost same as those of theoretical analysis. Furthermore in SSAM analysis with VISSIM simulation log, the number of high risk collisions decreased 36.0 %. However, the total delay decrease effect is not real meaning of decrease effect because the drivers' desired speed is same whether the VSL model is operated or not. Nevertheless this VSL model maintains free flow speed for longer and increases the cycle of traffic speed fluctuation. In other words, this is decrease of delay occurrence and scale. The decrease of speed gap between upstream and downstream stabilizes the traffic flow and leads decrease number of high risk collision. In conclusion, we can expect increase of safety through total delay minimization according to this VSL model.

• Journal of Korean Society of Transportation
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• v.23 no.3 s.81
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• pp.85-94
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• 2005

The scale and operating conditions of logistical systems very sensitively varies according to the variation of traffic intensity that is affected by the arrival characteristics of trucks and the attributes of loading/unloading services in logistics facilities. More exactly, logistics costs are incurred according to variations of traffic intensity. which are intimately linked with in a given time period. Also. although traffic intensity changes minutely, the range of cost variation is wide. Nevertheless, with regard to operating logistics systems, the existing studies make no attempt to analyze these factors. Therefore, it was the purpose of this study to determine the optimal traffic intensity to minimize excessive logistics costs resulting from the generation of unnecessary costs such as waiting costs and overcosts in operating a facility. For the purposes of this analysis. a determination model of optimal traffic intensity was constructed according to queuing theory. The inflow/outflow conditions of trucks and the terminal operational conditions were collected from an off-dock container terminal in Busan. On the basis of this data. the optimal traffic intensity that could off-set excessive waiting and operating costs was determined quantitatively. Also. using the optimal traffic intensity to be determined. we consider the improvements of operating system in the logistics facilities.