This Excel application includes calculations and graphs for various travel time functions discussed in this paper - AKÇELIK, R. (1991). Travel Time Functions for Transport Planning Purposes: Davidson's Function, its Time-Dependent form and an Alternative Travel Time Function. Australian Road Research 21 (3), pp 49-59. (Minor revisions: December 2000).
Akcelik & Associates (1991). Akçelik's_Travel_Function_(for 1991 paper)_v1.xls.