The focus of this research is to develop a bus dwell time model based on formulas presented in the Highway Capacity Manual (HCM) and Transit Capacity and Quality of Service Manual (TCQSM). The dwell time model proposed in this paper not only includes factors like the number of boarding and alighting passengers, but a number of secondary factors like crowding in the bus, crowding in the station, roadway congestion, bus type, the status of bus lines, the number of alighting passengers, the number of boarding passengers, level of service of the station before passengers alighting, level of service at the bus before passengers alighting, bus type, level of service at the bus after passengers alighting, the number of bus lines passing through the station, the average headway of bus lines, and level of service of roadway are considered and taken into account in our proposed model as well. Furthermore, the developed model is validated using data collected from bus lines in Tehran, Iran. The model validation demonstrates that it has relatively good accuracy (85%) to estimate the bus dwell time. Moreover, the sensitivity analysis on the developed model indicates that increasing the number of alighting passengers and crowding at the bus has a greater effect on the dwell time than any other factors. Decrease in level of service of roadway, increase in the number of boarding passengers, crowding at the station, and decrease in the average headway of bus lines are the other important factors respectively.