At the strategic level, multimodal freight network design problems are limited in that they reflect the costs and constraints associated with emissions. The network design problem (NDP) addressed in this study determines investment alternatives for minimizing total system cost, including costs related to greenhouse gas (GHG) emissions, while satisfying the emissions constraint. The NDP can accommodate improvement alternatives in transfer terminals as well as in road and railroad links. In this study, mode-specific travel time functions were used to represent the differences between the modes explicitly, even for the transfer facility. Emission factors were calculated by link travel speed and level of facilities. The empirical application to a container freight network from the Port of Pusan in southeastern South Korea showed the optimal investment strategy for meeting emissions reduction policy objectives. The conclusion is that investment should concentrate on railroad and terminal facilities to induce modal shift. In contrast, investment in congested roads might be a better option for corridors in which the level of railroad service is low and short-distance freight demands are dominant. These results indicate that the proposed network design problem can provide the appropriate investment strategy for reducing GHG emissions and therefore can be a useful approach with regard to GHG emissions reduction policy.
In Korea, almost 700 industrial parks are under operation. Generally, industrial parks consist of national industrial parks and local industrial parks which are managed by a central government and by local governments respectively. The developing countries such as Korea, China and Vietnam etc. have constructed many industrial parks, which result in the change of land use pattern and also affect future trip demands. Therefore, in estimating traffic demands, it is very important to consider the industrial park development. This study aims to improve the methodology in estimating a freight trip generation rate with the data based on a nationwide commodity freight survey. The result showed that it is desirable to apply freight trip generation rate by the industry sector in estimating freight trip generations and using the production area of firm as an indicator. Specially, the reliability of the rates through a survey could be made sure because a sample rate based on firms in industrial parks was over 25% and the response rate was over 67%. The sample rate and response rate are very superior as compared to surveys conducted in many other countries. Because industrial parks have significant effects on forecasting transportation demand in pre-feasibility studies of transport and logistics projects, it is expected that the accuracy of freight trip demands would be improved through the results of this study.
Fluctuations in roadway capacity due to non-recurrent traffic incidents is a source of uncertainty of travel time. Travel time reliability, as a transportation performance measure, which may reflect travel time uncertainty was applied to network analysis. Recently, research which applies network reliability concepts to transportation network design has been undertaken. In this study, a continuous network design problem (CNDP) with a travel time reliability constraint was formulated as a bi-level model. A simulation-based genetic algorithm with penalty method was used to obtain the optimal capacity enhancement of each link, combined with a routine which estimates travel time reliability under fluctuations of link capacity. The effect of the travel time constraint on a CNDP was analyzed through a numerical experiment using a simple network. Additionally, the effect of budget allocation and factors to be specified in the model on the results were analyzed.
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