Induced travel demand in developing countries:: Study on state highways in Turkey

Induced travel demand is a critical phenomenon for developing countries because neither road network nor the vehicle ownership have reached their contended phases. This leads to the opinion that induced demand is valid for developing countries or increase in travel demand is only a result of rapidly rising vehicle numbers and other socioeconomic parameters. In this study, induced demand estimation methodology is modified from the point of view of a developing country by introducing the application of tendency comparison of lane mile elasticities under different lag terms for control and highway investment data. Beside vehicle miles traveled, travel per vehicle (TPV) and number of vehicles for long-term effects are tried as new demand indicators. The selection of socioeconomic variables is also considered more expediently because of their rapid and wide changes in developing countries. The travel data of Turkish state highways are used for application. TPV is found to be the most distinguishable criterion of induced travel demand for Turkey with 2.0 times relative increase for private TPV and 3.5 times for commercial TPV. Demand elasticities based on commercial travel are found to be more permanent than the private travel based ones. Besides, longer peak period, which indicates the maximum difference in elasticity of control and test data, is obtained as 5 years for commercial travel which is 3 years for private purposed travel in lag consideration based on road supply conditions.