• Journal of Navigation and Port Research
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• v.29 no.8 s.104
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• pp.723-733
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• 2005

This paper presents a deadlock avoidance method for AGVs in automated container terminals. For a more efficient use of AGV traveling area, we divided the area into small-sized grids not enough to cover a whole AGV. Our deadlock avoidance method controls AGVs by identifying strongly connected components(SCCs) in a graph derived from the paths of AGVs on the grids. Also in this paper we suggest a route selection scheme which selects a route by predicting and comparing travel times of candidate routes by using a regression formula. Simulation experiments have shown that the proposed method can control AGVs for 48 hours without deadlocks and the count of AGV visits per QC is increased by $2\~10$ an hour.

• Journal of the Korean Society for Railway
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• v.8 no.2
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• pp.145-154
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• 2005

Traffic accidents at highway-rail crossing result in larger social and economic damages than the accidents at the typical highway intersections. The traditional control and warning systems of the highway-rail crossing have limitations in that 1) they do not recognize the differences of the trains' arrival times because they rely on the distance-based control system, rather than the time-based one, and 2) thereby they usually cause longer delays of vehicles and pedestrians at the highway-rail crossings. The objective of this study is to develop a time-based railroad crossing control system which takes into account the speed and expected arrival time of trains. using the spot speeds and acceleration rates of trains measured at three points, the developed system was found to be able to accurately estimate the arrival time of train. VISSIM simulation package was utilized to compare system effect of the developed time-based railroad crossing control system with that of the conventional distance-based one. It was found that the developed time-based railroad crossing control system reduced the average travel time, maximum delay length, average delay time, and average number of stop-experienced vehicles as much as 7.0$\%$, 75.6$\%$, 12.7$\%$, and 60.0$\%$, respectively, compared with those from the conventional distance-based one.

• Journal of Korean Society for Atmospheric Environment
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• v.28 no.1
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• pp.94-104
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• 2012

The purpose of this research is to quantify the compliance of on-road emission from a light duty diesel vehicle, based on a comparison to emission regulation standard. $NO_x$, CO and THC emissions were measured using a portable device on a selected real-world driving route with a length of approximately 22 km. On-road measurements were repeated by 10 times on a same route to reflect variability in traffic conditions. A test route was divided into 22 road links with length of 1 km to analyze emission results with higher spatial resolution. The average emissions of $NO_x$, CO and THC over total travel distance, which is approximately 220 km, were quantified to be in compliance with emission regulation standards. Under higher spatial resolution, $NO_x$ concentration exceeded a standard in 92 links out of 220 links. The extended time in stop period and the stop-and-go driving cycle were identified as two important reasons for increased $NO_x$ emissions in observed cases. Heavy traffics showed higher $NO_x$ emissions than free flow. These results indicate that the real-world vehicle emissions might exceed the compliance level associate with traffic conditions. Another interesting observation of this research is that the on-road emission characteristics can be independent to the average speed of road links with higher spatial resolution. Variability in on-road emission might not be fully described by solely relying on an average speed, because variability in traffic conditions and road conditions can influence on real-world vehicle emissions.

• KIEAE Journal
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• v.13 no.2
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• pp.67-76
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• 2013

The purpose of this study is to analyze the accessibility to the place for outdoor exercise. For that, the departure (resident) location of the users of outdoor exercise equipment within 12 parks in Seoul have been investigated. A total of 1,733 people have been surveyed during the two-week period between Aug.2 and Aug. 15 and 815 cases were analyzed. We also investigated demographic characteristics, access method and related factors such as location, climate and visiting time. The results were coded through ArcGis program and the accessibility to each exercise location, difference in regional accessibility and accessibility characteristics in terms of climate and time have been analyzed. The results are as follows: First, visitors to the Han River start from the places further than the visitors to the streamlines. Second, the average moving distance is longer for the users aged under-60 than for the users aged 60 and over to reach the exercise place. And the average moving distance for visitors to the Han River destination is the longest with 748 meters, followed by 203 meters for general parks and 92 meters for streamline parks, respectively. Third, in each non-waterfront parks, the moving distance by users under-60 was longer by about 230 meters than that by users 60 and over. Fourth, exercisers in the weekend travel more by 244 meters than those during the midweek users to reach the exercise place. Fifth, the number of visitors to the Han River increased in the weekend while visitors to the streamlines decreased in the same period. Sixth, the traveling length for bicycle users is three times as much as that for pedestrian visitors. And the departure locations of bicycle users were more widely distributed.

• Health Policy and Management
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• v.21 no.1
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• pp.23-43
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• 2011

Access to health care is complicated to define. It is a multidimensional process. In addition to the matters of quality of care, geographical accessibility and availability of the right type of care, finance, and acceptability are all involved. The purposes of this paper are to measure the geographic distances between patient residency locations and health service organizations in which the patients hadvisited, and to investigate the association between geographical distance measures and variables involved in health service utilization. The study used the first and the second wave of the 2008 Korea Health Panel Survey. The samples of analyses were patients who had visited outpatient or used ambulatory health services, and the total observations (visit numbers) analyzed were 229,128. We divided the samples into a frequent-visit illness group (Group 1) and a non-frequent visit illness group (Group 2) based on over 5,000 total visit numbers. We exploited three level analyses using xtmixed of STATA${\Box}$ 11.1 command with/without interaction terms among age, sex, and occupation. Geographical distances were measured using the Haversine method. Group 1 was tended to older and lower equivalent income than those of Group 2, but the geographic difference were not observed in terms of area deprivation index and standard mortality ratios. Amongst group 1, diabetes mellitus patients travelled far to visit health care organizations, and arthritis patients were more deprived in terms of the personal and areal characteristics. The study revealed that residents in rural areas traveled about 10 times more long distances than those whom lived in larger cities after adjusting for various variables, which we used for analyses. This study contributed to the practical understanding of health service utilizations using empirical analyses, and found that the types of diseases and socioeconomic characteristics of patients tended to define the amount of travel distance to healthcare organizations.

• Journal of the Ergonomics Society of Korea
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• v.30 no.5
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• pp.659-669
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• 2011

Objective: The aim of this study is to suggest a package layout guideline for low-floor bus by interview with passengers and observations of their behavior. Background: Increasing attention has been introduced the low-floor bus to be more suitable for use by transportation handicapped. Complex issues are involved in providing comfortable services to all people. We are going to suggest package layout guidelines for more comfortable and suitable travel to all people. Method: The two times of survey and video observation sessions were conducted on low-floor buses in Seoul; (1) a finding of potential issues in the first session, (2) a confirming of issues from the last session. Results: The three of major issues were founded in this study; (1) difficulties in supporting body when standing, (2) difficulties in sitting on front wheel pan seat, (3) difficulties in passing through the aisle. Conclusion: There were clear differences between public and transportation handicapped in using some tools which are used for support body such as roof hand rails, side hand rails, and hand rail rings. Some of design problems were founded to improve from the perspective of ergonomics and universal design. Such differences and design guidelines have to be considered in bus design as well as commercial vehicle. Application: The proposed design guidelines can be used to development of low-floor bus and other public transportations.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.3
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• pp.50-58
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• 2017

TPCLT(Twice Per Cycle Left-turn) operation reduces this left-turn 'spill-over' problem on an as needed basis by servicing the protected left-turn movement as a leading and a lagging left-turn. In this study, to evaluate the effectiveness of TPCLT applied to three-legged signalized intersection in Korea, the analysis was carried out using VISSIM and SSAM model analysis. The study was implemented by three cases which are TPCLT operation, non-TPCLT operation and half-cycle operation using VISSIM program. According to the 9-left-turn volume scenario, total delay and travel times of each case was analyzed by VISSIM program. The study result shows more effective applying TPCLT operaion in the present ~ +50% scenario area at the intersection in terms of total delay.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.12
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• pp.1328-1336
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• 2012

Compared to terrestrial RF communications, underwater acoustic communications have several limitations such as limited bandwidth, high level of fading effects, and a large underwater propagation delay. In this paper, in order to tackle those limitations of underwater communications and to make it possible to form a large underwater monitoring systems, we propose a hierarchical underwater network architecture, which consists of underwater sensors, clusterheads, underwater/surface sink nodes, autonomous underwater vehicles (AUVs). In the proposed architecture, for the maximization of packet delivery ratio and the minimization of underwater sensor's energy consumption, a hybrid routing protocol is used. More specifically, cluster members use Tree based routing to transmit sensing data to clusterheads. AUVs on optimal trajectory movements collect the aggregated data from clusterhead and finally forward the data to the sink node. Also, in order to minimize the maximum travel distance of AUVs, an Integer Linear Programming based algorithm is employed. Performance analysis through simulations shows that the proposed architecture can achieve a higher data delivery ratio and lower energy consumption than existing routing schemes such as gradient based routing and geographical forwarding. Start after striking space key 2 times.

• International Journal of Highway Engineering
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• v.12 no.4
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• pp.139-145
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• 2010

An integrity testing for stone columns was attempted using crosshole S-wave logging. The method is conceptionally quite similar to the crosshole sonic logging (CSL) for drilled piers. The critical difference in the logging is the use of S-wave rather than P-wave, which is used in CSL, because swave is the only wave sensing the stiffness of slower unbounded materials than water. An electro-mechanical source, which can generate reversed Swave signals, was utilized in the logging. The stone column was delineated using the S-wave travel times across the stone column, the S-wave velocity profile of the crushed stone($V_{cs}$-profile) and that of surrounding soil($V_s$-profile). In the calculation of $V_{cs}$-profile of the crushed stone, its friction angle and Ko (coefficient of lateral earth pressure at rest) are recommended to be used. The calculation of the column diameter is not much affected by the values of friction angle and Ko.

• International Journal of Highway Engineering
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• v.18 no.1
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• pp.99-107
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• 2016

PURPOSES : This study was initiated to estimate expressway traffic congestion costs by using Vehicle Detection System (VDS) data. METHODS : The overall methodology for estimating expressway traffic congestion costs is based on the methodology used in a study conducted by a study team from the Korea Transport Institute (KOTI). However, this study uses VDS data, including conzone speeds and volumes, instead of the volume delay function for estimating travel times. RESULTS : The expressway traffic congestion costs estimated in this study are generally lower than those observed in KOTI's method. The expressway lines that ranked highest for traffic congestion costs are the Seoul Ring Expressway, Gyeongbu Expressway, and the Youngdong Expressway. Those lines account for 64.54% of the entire expressway traffic congestion costs. In addition, this study estimates the daily traffic congestion costs. The traffic congestion cost on Saturdays is the highest. CONCLUSIONS : This study can be thought of as a new trial to estimate expressway traffic congestion costs by using actual traffic data collected from an entire expressway system in order to overcome the limitations of associated studies. In the future, the methodology for estimating traffic congestion cost is expected to be improved by utilizing associated big-data gathered from other ITS facilities and car navigation systems.