• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.5
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• pp.40-51
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• 2020

Much time has passed since Korea's expressway congestion-threshold speed was revised in 2011. In the meantime, various expressway environments have changed owing to improved performance of vehicles, expanded operations of transport competition (i.e., the KTX), and increased speed limits along some expressway sections. In addition, the speed that expressway users expect to travel at is also increasing. Therefore, through a survey, this study investigates expressway users' perceptions of congestion, and reviews the adjustment of the expressway speed congestion threshold by analyzing expressway traffic flow. One result of the survey confirms that the threshold speed expressway users consider to be congestion has slightly increased. Analyzing traffic and speed data through a K-means algorithm found that the threshold speed for congestion is 60 km/h. In addition, assuming the congestion threshold speed increase from 40 km/h to 50 km/h and 60 km/h, frequently congested expressway sections are identified, determining that 50 km/h is appropriate as a congestion threshold for proper expressway mobility management.

• International Journal of Highway Engineering
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• v.13 no.3
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• pp.177-184
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• 2011

There are several differences between freeways and general national roads in terms of structures, conditions and limited speeds. Likewise, the characteristics of $CO_2$ emission in these roads differ depending on the road types. For these reasons, it is necessary to compare the two types of roads in terms of $CO_2$ emissions. The study was performed targeting Gyeongbu Expressway and National Highway 1. Firstly, the amount of $CO_2$ emission each car was compared in the whole sections of the both. Secondly, top 10 sections were picked out, and then $CO_2$ emission each section were compared. Lastly, two sections which were with the highest and lowest amount of $CO_2$ emission per car, were compared. As results, it were found that there were less amount of $CO_2$ emission on freeways. because cars are running on uniform velocity at relatively high speed, and that there were more amount of $CO_2$ emission on the national highway. because of frequent intersections and associated congestion. It may be concluded that the amount of $CO_2$ emission at the national highway could be reduced if signal coordination and intersection intervals are improved there.