AN AGGREGATE DEMAND MODEL FOR INTERCITY PASSENGER TRAVEL IN SRI-LANKA

Inspite of the inherent weaknesses in aggregate demand models, they co ntinue to be used in everyday applications, especially in developing c ountries. The largely data intensive disaggregate model preclude its a pplication in many cases. This paper attempts the formulation and cali bration of an aggregate total demand model for estimating inter-distri ct passenger travel by public transport in Sri Lanka. In its process, an investigation is made of the common problems in the aggregate appro ach while examining possible remedial measures to improve the accuracy and (hence) the usability of the aggregate model. It is argued that c ommonly used variables and functional forms are inappropriate for maki ng accurate estimates in developing countries. Consequently, the model calibration is shown to incorporate variables representing urbanisati on, under-development, transfers, a mode-abstract cost function and in trinsic features. The necessity for functional form for each variable to be based on behavioral assumptions that are tested using the Box-Co x transformation for ensuring the best fit of the data is also observe d. Although, the model form was calibrated for Sri Lanka, the model is generalised in order for its applications to other countries as well as, both, inter-district and intercity travel demand estimation.