This study aims to develop an underground expressway design for an exit area to mitigate traffic congestion. Thus, we explain the necessity of underground expressways and three reasons for persistent congestion on underground expressways despite an increase in supply. We focus on the first reason, which is a complicated traffic-flow conflict in the exit area, and analyze the traffic flow based on various conditions, such as the exit rate to a nearby interchange and the exit location for underground and ground roads. Consequently, we identify three factors that affect congestion in the exit area. The first factor is the exit rate, where a higher exit rate corresponds to a more severe congestion. The second is the exit location of two roads. When the exit of a road that exhibits a higher exit rate is placed on a curb side, the average delay is reduced. The final factor is the length of the lane-change section, where a longer lane-change section correspond to less congestion. However, after a certain length, the change in congestion is negligible. Based on these results, we suggest revised design guidelines for underground expressways in terms of exit location and the length of lane-change sections.

ABSTRACT
1. 서론
2. 현황 분석 및 기존 연구 고찰
    2.1. 현황 분석
    2.2. 기존 연구 고찰
    2.3. 본 연구와의 차별성 및 목적
3. 지하도로 진출부 위치 및 차로변경거리 분석
    3.1. 시나리오 구성
    3.2. 지하도로 설계지침 적용 결과
    3.3. 시뮬레이션 분석 결과
지하도로 설계지침 개정안 제시
    4.1. 지하도로 진출부 위치
    4.2. 차로변경 거리
5. 결론
감사의 글
REFERENCES

• 방수혁(한국교통연구원 도로교통연구본부 부연구위원) | Bang Soohyuk Corresponding author
• 이진각(㈜내일이엔시 도로교통안전연구소 소장) | Lee Jinkak
• 박상현(㈜내일이엔시 도로교통안전연구소 사원) | Park Sanghyun