Waiting time is a major undesirable component of travel time that can significantly affect mode choice and station design in urban public transportation systems. While most previous work discusses waiting time in single-route problems, there is a limited number of studies that have considered waiting time at a stop with multiple routes serving the same origin and destination. This specific situation is commonly referred to as the common-line problem in the literature. Preceding research in this scope primarily investigated waiting time with random arrival of passengers at a stop, however, passengers can plan their arrival to adjust their waiting time. Moreover, waiting time has been examined at the origin stop only, while it can also be incurred at the destination. Given the mentioned gaps and considering different situations, previous discussions on the mean waiting time in a common-line problem may not be valid any longer. Therefore, an analytical approach was developed to describe the mean waiting time of passengers using a case scenario of regular and express buses. The result of this study can be used to enhance ridership in routes with shared origin and destination.