Travel time uncertainty due to traffic condition is an important factor in planning Emergency Medical Services (EMS). In the study, we analyzed the district-wide service capability of dispatch centers with various descriptive statistics and variability measures to determine the vulnerability of a specific region to the traffic condition. We introduced Response Time Variability (RTV) index to evaluate such vulnerability. RTV index, which is unitless, has implications that higher RTV means that the region under evaluation has higher variability to the traffic condition, while lower RTV means that the region is less prone to the travel time uncertainty. To derive RTV, time-varying speeds are defined for each street segment within a street network based on the historic traffic speed data. We generated a 5-minute travel time contour for fire and emergency dispatch centers in Seoul and calculated the corresponding time-dependent coverage areas for three time periods on each day of week.
In this paper, we calculate RTV with two variables using GIS-based approaches: 5-minute coverage area and the number of population inside the 5-minute coverage area. First, we focus on the evaluation of EMS performance of dispatch centers by district. A vulnerability map of EMS performance of dispatch centers is drawn, and Jung, Yongsan, Seocho, and Yangcheon districts are classified as the most vulnerable region to traffic effects, having RTV values greater than 0.7. It is observed that vvariability measures derived from coverage and from population inside coverage are strongly correlated to each other. Then we examine correlation coefficients between variability measures derived from GIS-based approaches and variability of actual ambulance travel times taken from EMS call data in order to examine to what extent the GIS-based approaches approximate reality. There is a strong positive linear correlation (r=0.7) between the variability measures based on GIS-based approaches and variability measures based on actual travel time, meaning that the GIS-based approaches well reflect the reality.
Secondly, we focus on the evaluation of EMS performance within jurisdictions of dispatch centers by district, and it is found that EMS response in Seocho and Gangnam are most sensitive to traffic condition. We divide Seocho and Gangnam district into 100m-by-100m grids to figure out which part of area is exposed to travel time uncertainty originating from time-of-day and day-of-week traffic effects. A map of travel time uncertainty in the two districts is obtained, and the minimum required k such that all areas or all populations can be served by an ambulance within k minutes is determined for each district.
In the study, it is shown that RTV differs from district to district, meaning that the sensitivity of EMS response performance to traffic condition is different by city districts. Based on the capability of RTV in identifying regions with high traffic variability, it can be used as a new performance measure of EMS.
응급의료체계에서 긴급차량의 신속한 현장 도착 및 구급처치는 사고 피해자의 생존과 매우 밀접한 관련이 있다. 주요 국가에서 사고현장에서의 초동 조치에 영향을 미치는 긴급차량의 현장 도착시간 개선을 위한 노력을 하고 있으며, 한국에서는 2017년까지 74%의 긴급 상황에 대해 119 출동부터 사고현장 도착까지 5분 내 현장 도달하는 것을 목표로 하고 있다. 본 연구에서는 서울시의 지리정보체계 (GIS) 도로망 정보와 교통속도 데이터를 바탕으로 119안전센터의 출동범위와 출동범위 내의 거주인구 수를 분석하여, 각 요일의 시간대별 교통속도에 따라 유동적으로 변하는 값의 추이를 도출하고 그 변동성을 분석하고자 한다.
이에 본 논문에서는 반응시간변동성 (Response Time Variability) 지수를 도입하여 서울시 119 안전센터별 교통속도에 따른 응급의료서비스의 변동성을 측정하였고, 중구, 용산구, 서초구, 양천구에 속한 안전센터들이 가장 취약한 것으로 밝혀졌다. 실제 구급일지 데이터의 구급차 이동시간(travel time)의 변동성과 GIS에서 계산한 출동범위 및 출동범위 내 인구의 변동성간의 상관관계를 측정한 결과 r=0.7에 근접한 값을 나타냈고, 이는 GIS를 이용하여 측정한 응급의료서비스가 실제와 유사한 패턴을 나타내고 있음을 알려준다.
또한, 서울시 소방관할별 교통속도에 따른 응급의료서비스 변동성을 측정하였고, 서초구와 강남구 지역의 응급의료서비스가 가장 교통속도 변화에 취약한 것으로 밝혀졌다. 서초구와 강남구를 100mX100m 그리드 형태로 나누어서 어느 특정 지역이 가장 교통속도 변화에 취약한지 계산하였고, 두 구역의 동을 대상으로 구급차가 전체 영역 혹은 전체 인구를 k분 내로 서비스 할 수 있는 k의 최소값을 구하였다.
