Due to rapid increase in car ownership and other related factors we often experience traffic Jam at intersections with formation of long queues. This is a common phenomenon in major cities of Pakistan. In order to solve this problem it is necessary to review the traffic signal setting. For a particular junction cycle time is an important parameter to minimize delay which ultimately causes formation of long queues and accidents. The most important factors in determining the optimum cycle time is saturation flow and lost time. Direct measurement of saturation flow is obviously desirable to achieve satisfactory results, but in case of new intersection, results from measurements of saturation flow are being estimated from the work of previous researchers. In case of Pakistan where no standard value of saturation flow and lost time are available pertaining to local traffic condition, values used in developed countries are being applied resulting in non achievement of optimum cycle time. This thesis describes experimental research which is carried out for estimating the saturation flow and lost time under local conditions of Karachi. Data was collected by video recording of traffic flow at eighteen (18) signalized intersections along two major arterials, namely Shahra-e-Faisal and M.A. Jinnah Road, of Karachi city. Recorded data was analyzed in laboratory to retrieve the information on the headway of all the vehicles in saturated cycles. The analysis of PCU values were carried out by comparing the average car headway with the average headway other vehicle type. Different studies show a great deal of variations in saturation flow rates and start-up lost times. This indicates a lack of stability. This is acknowledged in the HCM. Due to these instabilities, the HCM recommends that local data collection be performed to produce more accurate estimates of local saturation flow rates and start-up lost times. It is a known fact that there are close relationships between intersection characteristics and saturation flow. Empirical relationships have been developed for estimation of saturation flow and lost time for many countries such as Great Britain, Australia, U.S.A, Bangkok, Malaysia, India and Bangladesh etc but such relationship not developed for Pakistan as yet. vAn effort has been made in this research to derive empirical relationship between intersection characteristics (approach width) and saturation flow. Appropriate PCU values as per local traffic conditions have been calculated for saturation flow estimation. This is for the first time in Pakistan that such values, based on local traffic, has been calculated. In this thesis, an effort has been made to establish relationship between saturation flow and approach width and comparison of the results of has been carried out with previous work done. The major focus of this thesis is on measurement of departure headways at selected signalized intersections in Karachi (Pakistan) and to gather as much basic information as possible which can be used in the analysis of the collected data as required in the thesis. As outcome of the research, relationship has been established, through predictive models, for the estimation of saturation flow in Pakistan. The results obtained have a very practical application potential in Karachi and in urban areas of similar traffic characteristics.