The expressway users are dissatisfied with the increased traffic time after implementation of weekday bus only way policy. This paper describes the time zone for flexible operation plan of weekday bus only way to improve traffic flow rate and to reduce the heavy traffic of non-bus only way. There are Travel Time Index (TTI) data by the time and day based on the information for traffic volume and traffic speed of each lane according to the vehicle type. There are three cases in accordance with flexible operation plan of weekday bus only way policy. Case 1) TTI is 1.2, Case 2) TTI is 1.4, Case 3) TTI is 1.8. In summary, the authors have decided Case 2) as the most optimum service level. In accordance with, we suggest that flexible operation time zone, which is needed further study related economic analysis, is from 9 am to 6 pm in direction of Busan and from 9 am to 1 pm in direction of Seoul.