A NEW LOOK AT DAVIDSON'S TRAVEL TIME FUNCTION

Abstract

The paper discusses the equivalency of Davidson's travel time-flow function, which was originally derived using a queueing theory approach, and Mosher's hyperbolic cost function, which was proposed as one which has the property that the change in cost per unit of flow as flow increases is small for low flow values, but large as capacity is approached. A modified version of the function is given which yields finite values of travel time for oversaturated region of flow. It is shown that the use of the function is not limited to use with any particular type or technique of assignment. The marginal and integral travel time functions are presented in addition to the average and total travel time functions so that assignments according to both user-optimising and system-optimising principles can be carried out using either a heuristic iterative loading (capacity-restraint type) or a mathematical optimisation (equilibrium type) technique. /Author/TRRL/

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