Traffic congestion and bottleneck are usually observed at toll plaza areas in a freeway system. Implementation of an electronic toll collection (ETC) system is not only able to increase toll plaza throughputs and reduce toll collection time, but it also helps to increase freeway users' safety level and convenience as well as resolve energy consumption and air pollution problems. It is expected to improve the problems associated with traffic congestion and environmental impact at toll plaza areas. Since the formal implementation of ETC in the freeway system of Taiwan, the Taishan toll station has been encountering the most ETC lane usage in both directions. The ETC traffic demands have also reached the threshold of increasing one more ETC lane in each direction. However, some concerns are raised by the general public since extra delays might occur in the manual toll collection lanes. Therefore, in view of the limited freeway resources, there is a crucial research topic on the reasonable allocation of ETC and manual lanes at a toll station under the considerations of freeway users' demand and economic benefits. To tackle this problem, this research first constructs a time series model using the historical traffic flow data to estimate the ETC traffic flow patterns and compares the predicted ETC traffic flows to the observed data to verify the reliability of the constructed time series model. In addition, this research adopts a toll plaza simulation (TPS) model to evaluate the effects of ETC lane allocation and usage on the overall service performance at the Taishan toll station. The empirical study results indicate that the ultimate goals of implementing the ETC system might not be achieved by simply considering the ETC lane usage rate as the only one criterion to open new ETC lanes. The outcomes of this research can be a beneficial reference for the freeway management agency to determine the appropriate timing for adding additional ETC lanes and other relevant polices.