If an incident occurs on the road, the normal flow of traffic stream is interrupted and the road capacity reduces. This thus leads to huge social, economical losses, such as traffic congestion, air pollution, etc. This study was conducted to examine an effect on an incident management system by carrying out an simulation analysis and an social cost analysis. For the simulation analysis, incidents in a normal situation were compared with those in an incidental situation and thus travel time, queue length, and accident duration were selected as an evaluation indicator. It was analyzed that after an incident situation occurs, the length of vehicle in waiting rapidly increases and thus travel time also largely increases. To make an social cost analysis, vehicle operation cost (VOC) and vehicle operation time (VOT) were used an index. The results showed that travel time cost per driver and vehicle in an incidental situation all increased, compared with that in a normal situation. It was also observed that the longer the lasting hours are, the higher the travel time increases.