A highway capacity function in Korea: Measurement and calibration

Capacity functions are important in the model that accounts for the user’s route choice behavior based on the traveller’s perception of the travel time. This is because a capacity function represents the relationship between the traffic volume and the travel time on the link. The capacity function developed by the U.S. Bureau of Public Roads (BPR) has been used in many countries, including Korea, without much effort to calibrate the parameters for its own transportation environment. Countries other than the United States, however, have distinctive demographic, economic, cultural, and behavioral characteristics; and they might need unique capacity functions for their own environments. Thus, it is important for Korea to have its own capacity function that can appropriately represent the Korean highway environment. Any attempt to model the Korean highway system without using a suitable capacity function might result in inappropriate solutions, because most modeling activities are crucially based on link travel time, and it is the capacity function that furnishes those link travel time. A link capacity function for Korea is calibrated based on a BPR type formula utilizing an alternative method. The alternative method is developed in a bilevel programming framework that uses link volume counts instead of link flow and travel time data. Detailed calibration results are reported.