The most observable of the various problems besetting the expressway is the frequent occurrence of lane blockage caused by the overflowing of exiting vehicles in the main-lane roadway, especially during peak hours. This study investigates the effects of lane blockage on the traffic flow at the bottleneck section and to the volume pattern of the upstream section. It also tries to quantify the reduction of discharge as a function of the number of lanes blocked. Secondary and primary data from a video survey were used in establishing the expressway's traffic characteristics. Various traffic stream models were calibrated using on-site data to reflect current operating characteristics. Origin-destination data showed that interchanges located near the urban core have the highest demand of exiting traffic, particularly in the southbound direction, which captures 47.8% of the total exiting southbound traffic. The frequent occurrence of lane blockage ate these interchanges significantly reduces the capacity and influences traffic flow behavior of the expressway. It was found out that lane blockage causes a reduction of capacity as high as 49.88%. This results to the deterioration of level of service, manifested by excessive delay, instability of travel time and erratic stop-and-go operation. Model calibration showed that Underwood's model is best in terms of predicting capacity. The shockwave associated with the alternating trend of lane blockage and opening produced an oscillating behavior of density and pseed about their optimum values. This indicated that the occurrence of lane blockage has prevented the facility to sustain its operation at its optimum or near-optimum condition for a relatively long period of time.
