Variability of Travel Time, Users’ Uncertainty, and Trip Information

Travel time saving plays an important role in the socioeconomic studies of the profitability of transport projects. This paper presents some parts of the studies performed in collaboration with SETRA, a department of the French Ministry of Transport, on the economic evaluation of operating roads. The paper includes four main parts. The first includes a description of how travelers’ decisions are influenced by the variability of travel time. The statistical analysis of the recorded travel time on a motorway in île-de-France, France, is developed to quantify the variability of travel time and to measure its magnitude. The second section is devoted to developing the methodological framework to capture the safety margin considered by travelers in their trip-making behaviors. A model is formulated to reflect the behavior of the traveler before making a trip. This model highlights the effect of each travel component, the mean of the travel time, the level of variability, and the safety margin chosen by the traveler before traveling. The third section extracts the optimal safety margin that minimizes the cost of the total time allocated to travel. The last section of the paper is devoted to some algebraic manipulation to characterize the features of the output if the variability of travel time in the economic evaluation of transport projects is incorporated. An expression is also given for the gain that operators bring when they reduce the variability of travel time or reduce the uncertainty that travelers feel by providing them with information.