• Journal of Korean Society of Transportation
• /
• v.27 no.5
• /
• pp.209-221
• /
• 2009

Travel time estimation under given traffic conditions is important for providing drivers with travel time prediction information. But the present expressway travel time estimation process cannot calculate a reliable travel time. The objective of this study is to estimate the path travel time spent in a through lane between origin tollgates and destination tollgates on an expressway as a prerequisite result to offer reliable prediction information. Useful and abundant toll collection system (TCS) data were used. When estimating the path travel time, the path travel time is estimated combining the link travel time obtained through a preprocessing process. In the case of a lack of TCS data, the TCS travel time for previous intervals is referenced using the linear interpolation method after analyzing the increase pattern for the travel time. When the TCS data are absent over a long-term period, the dynamic travel time using the VDS time space diagram is estimated. The travel time estimated by the model proposed can be validated statistically when compared to the travel time obtained from vehicles traveling the path directly. The results show that the proposed model can be utilized for estimating a reliable travel time for a long-distance path in which there are a variaty of travel times from the same departure time, the intervals are large and the change in the representative travel time is irregular for a short period.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2021.06a
• /
• pp.49-49
• /
• 2021

홍수 발생 시 제내지에 존재하는 도로 및 상·하수도시설물은 저지대를 중심으로 생성되는 침수지역이 아닌 대부분 집중호우, 태풍으로 인해 발생한 유출량이 지표면 유출로 이어져 지면 경사를 따라 유하하면서 흐름을 방해하거나 노후된 시설물 등에서 피해가 발생한다. 이러한 피해발생 특성을 고려하여 홍수피해액을 추정하기에는 침수면적과 시설물 현황 등을 활용하는 기존의 손실 함수 개발 방법으로는 부족한 부분이 존재하며, 유수 흐름의 주요 인자인 침수심, 유속 등과 같은 수리특성을 고려하여 시설물에 대한 홍수피해액을 추정하는 방안이 필요하다. 본 연구에서는 수리특성을 고려한 시설물의 홍수피해액을 추정하기 위한 손실함수를 개발하고자 국가재난정보관리시스템(NDMS) DB에서 해당 시설물의 상세주소를 이용하여 피해 발생위치와 피해액을 파악하였으며, 2차원 수리해석 모형인 FLO-2D를 활용하여 시설물의 피해위치에서 발생된 수리특성 인자인 침수심과 유속을 분석하였다. 시설물의 단위면적 당 피해액을 종속변수로, 분석된 평균 침수심과 평균 유속을 독립변수로 선정한 후 변수 자료들의 신뢰성과 함수의 설명력을 향상시키기 위하여 이상자료들을 제거한 후 손실함수를 개발하였다. 본 연구에서 개발된 손실함수는 수리특성 인자인 침수심과 유속에 의하여 홍수피해액을 직접적으로 추정하는 방법으로 향후 홍수재해에 대한 사전 재산피해 추정을 통하여 합리적인 선제적 예방조치 등의 홍수재해 예방 활동 등에 활용될 수 있을 것으로 기대한다.

• The Journal of the Korea Contents Association
• /
• v.15 no.7
• /
• pp.414-427
• /
• 2015

Most Studies for office market have focused on large-scale office buildings. There is, if any, a little research for small and medium-sized office buildings due to the lack of data. This study uses the self-searched and established 1,056 data in Gangnam-Gu, and estimates the data by not only linear regression model, but also data mining methods. The results provide investors with various information of price determinants, for small and medium-sized office buildings, comparing with large-scale office buildings. The important variables are street frontage condition, zoning of commercial area, distance to subway station, and so on.

• Journal of Korean Port Research
• /
• v.12 no.1
• /
• pp.55-64
• /
• 1998

Directed graphic algorithm was applied to an empirical analysis of traffic occupant fatalities based on a model by Crandall. In this paper, Crandall's data on U.S. traffic fatalities for the period 1947-1981 are focused and extended to include 1982-1993. Based on the 1947-1981 annual data, the directed graph algorithms reveal that occupant traffic deaths are directly caused by income, vehicle miles, and safety devices. Vehicle mileage is caused by income and rural driving. The estimation is conducted using three stage least squares regression. Those results show a difference between the traditional regression methodology and causal graphical analysis. It is also found that forecasts from the directed graph based model outperform forecasts from the regression-based models, in terms of mean squared forecasts error. Furthermore, it is demonstrates that there exists some latent variables between all explanatory variables and occupant deaths.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.9
• /
• pp.5585-5593
• /
• 2014

This study tested the hypothesis that the significance of the heterogeneous dispersion parameter in safety performance function (SPF) used to estimate the expected crashes is affected by the endogenous heterogeneous prior distributions, and analyzed the impacts of the mis-specified dispersion parameter on the evaluation results for traffic safety countermeasures. In particular, this study simulated the Poisson means based on the heterogeneous dispersion parameters and estimated the SPFs using both the negative binomial (NB) model and the heterogeneous negative binomial (HNB) model for analyzing the impacts of the model mis-specification on the mean and dispersion functions in SPF. In addition, this study analyzed the characteristics of errors in the crash reduction factors (CRFs) obtained when the two models are used to estimate the posterior means and variances, which are essentially estimated through the estimated hyper-parameters in the heterogeneous prior distributions. The simulation study results showed that a mis-estimation on the heterogeneous dispersion parameters through the NB model does not affect the coefficient of the mean functions, but the variances of the prior distribution are seriously mis-estimated when the NB model is used to develop SPFs without considering the heterogeneity in dispersion. Consequently, when the NB model is used erroneously to estimate the prior distributions with heterogeneous dispersion parameters, the mis-estimated posterior mean can produce large errors in CRFs up to 120%.

• Journal of Labour Economics
• /
• v.29 no.1
• /
• pp.1-39
• /
• 2006

This paper documents the increase in earnings variability (or earnings risk) during the 1990s in Korea, and investigates whether it can be accounted for by capital market opening. The variances of transitory and permanent innovations in earnings are estimated from repeated cross-section data using a simple econometric framework. The increasing time-series pattern of earnings risk among men follows the increased foreign capital presence reasonably well, but the supporting cross-sectional evidence for a causal relationship between the two is weak. However, foreign direct investment (FDI) is found to have had some non-neutral effects on workers of varying skills in such a way that transitory earnings risk of less-skilled workers relatively increased with FDI. To the extent that transitory innovations are not fully insured, this widening effect of FDI on earnings risk gap may have contributed to widening welfare gap between skilled and unskilled workers in Korea, at least in terms of "risks."

• Environmental and Resource Economics Review
• /
• v.33 no.2
• /
• pp.159-178
• /
• 2024

This study aims to assess the direct and indirect impacts of local fiscal expenditures on water quality. Panel data spanning from 2010 to 2018 for 173 cities and districts in Korea are assembled, and a two-stage dynamic panel model is utilized for our estimation. The empirical findings reveal several key insights. Firstly, local fiscal expenditures on water quality are effective in ameliorating both Biological Oxygen Demand (BOD) and Total Phosphorus (T-P). Notably, the direct impact on T-P surpasses that on BOD in the short and long run. Secondly, expenditures dedicated to water quality improvement demonstrate a positive effect on local economic growth, and an inverted U-shaped relationship is observed between BOD and local economic growth. Due to the positive linkage, the indirect effect on BOD suggests, on average, a deterioration in water quality during local economic growth. Thirdly, concerning BOD, the direct effect of government expenditure on water quality improvement outweighs the indirect effect, but in the case of T-P, the indirect effect is not significant, and the total effect is solely determined by the direct impact. Despite local fiscal expenditures potentially exacerbating water quality through regional economic growth, the study finds that the direct enhancement of water quality remains a more substantial factor in the short and long run.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.387-387
• /
• 2022

기존 홍수기시 댐 운영은 예측 강우와 실시간 관측 강우를 이용하여 댐 운영 모형을 수행하며, 예측 결과에 따라 의사결정 및 댐 운영을 실시하게 된다. 하지만 이 과정에서 반복적인 분석이 필요하며, 댐 운영 모형 수행자의 경험에 따라 예측 결과가 달라져서 반복작업에 대한 자동화, 모형 수행자에 따라 달라지지 않는 예측 결과의 일반화가 필요한 상황이다. 이에 댐 운영 모형에 AI 기법을 적용하여, 다양한 강우 상황에 따른 자동 예측 및 모형 결과의 일반화를 구현하고자 하였다. 이를 위해 수자원 분야에 적용된 국내외 129개 연구논문에서 사용된 딥러닝 기법의 활용성을 분석하였으며, 다양한 수자원 분야 AI 적용 사례 중에서 댐 운영 예측 모형에 적용한 사례는 없었지만 유사한 분야로는 장기 저수지 운영 예측과 댐 상·하류 수위, 유량 예측이 있었다. 수자원의 시계열 자료 활용을 위해서는 Long-Short Term Memory(LSTM) 기법의 적용 활용성이 높은 것으로 분석되었다. 댐 운영 모형에서 AI 적용은 2개 분야에서 진행하였다. 기존 강우관측소의 관측 강우를 활용하여 강우의 패턴분석을 수행하는 과정과, 강우에서 댐 유입량 산정시 매개변수 최적화 분야에 적용하였다. 강우 패턴분석에서는 유사한 표본끼리 묶음을 생성하는 K-means 클러스터링 알고리즘과 시계열 데이터의 유사도 분석 방법인 Dynamic Time Warping을 결합하여 적용하였다. 강우 패턴분석을 통해서 지점별로 월별, 태풍 및 장마기간에 가장 많이 관측되었던 강우 패턴을 제시하며, 이를 모형에서 직접적으로 활용할 수 있도록 구성하였다. 강우에서 댐 유입량을 산정시 활용되는 매개변수 최적화를 위해서는 3층의 Multi-Layer LSTM 기법과 경사하강법을 적용하였다. 매개변수 최적화에 적용되는 매개변수는 중권역별 8개이며, 매개변수 최적화 과정을 통해 산정되는 결과물은 실측값과 오차가 제일 적은 유량(유입량)이 된다. 댐 운영 모형에 AI 기법을 적용한 결과 기존 반복작업에 대한 자동화는 이뤘으며, 댐 운영에 따른 상·하류 제약사항 표출 기능을 추가하여 의사결정에 소요되는 시간도 많이 줄일 수 있었다. 하지만, 매개변수 최적화 부분에서 기존 댐운영 모형에 적용되어 있는 고전적인 매개변수 추정기법보다 추정시간이 오래 소요되며, 매개변수 추정결과의 일반화가 이뤄지지 않아 이 부분에 대한 추가적인 연구가 필요하다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.2
• /
• pp.667-677
• /
• 2013

The introduction of a new transit facility affects mode share of travel alternatives. The multinomial logit model, which has been the most commonly used for estimating mode share, has difficulty in reflecting heterogeneity of travelers' choices, and it has a limitation on grasping their characteristics of mode choice. The limitation may lead to over- or under-estimation of the new transit facility and bring about significant social costs. This paper aims to find a methodology to overcome the problem of preference homogeneity. It also applies market segmentation structure of separating the whole population into direct and indirect beneficiary to consider their preference heterogeneity. A mode choice model is estimated on data from Jeju Province and statistically tested. The results show that mode transfer rate of direct beneficiaries that inhabit in downtown areas increases as the new transit facility provides more advanced services with higher costs. The results and the model suggested in this study can contribute to improving the accuracy of demand forecasting of new transit facilities by reflecting heterogeneity of mode-transfer patterns.

• International Area Studies Review
• /
• v.22 no.3
• /
• pp.67-84
• /
• 2018

The purpose of this paper is to investigate the Balassa-Samuelson effect that real exchange rate could deviate from its long-run equilibrium. To analyze this effect, I estimated the long-run relationship between real exchange and productivity using the dynamic panel ordinary least square(DOLS) and panel error correction model(ECM) after conducting the unit root and cointegration test. The results show that all variables except for the real exchange rate have the unit root. Then I conducted the cointegration test to find out whether there exist the stable long-run relationships. The results show that the variables are cointegrated and significant statistically. The DOLS and ECM methods are used to estimate the coefficient of the cointegrated variables. The major finding are that the estimates are statistically significant and that they show the same sign as the economic theory predicts.