Modeling and Distribution of Link Travel Times: An Analysis on Istanbul Freeways

Analyzing freeway travel times within a case study: Reliability of route traversal times

“…We initially assume that link traveling time, either extrapolated from GPS measurements [20] or recon structed by flow models [20], is a discrete random variable. Although there is a serious number of studies in which direct approximation of continuous functions to travel time data is sought, we needed such an assumption mainly for two reasons: The first is that we focus on the reliability of actual link and route traversal times rather than the temporal variation of point-wise measurement extrapolations on speed; and the second is to express appropriately the available data.…”

“…Such a shift to continuous random variable approach enables us to signify the unobserved elements of travel time sample space. In the following, measures of travel time those are obtained over a multi-lane freeway stretch in Istanbul in five consecutive days [20] are aggregated in terms of two directions, initially. Then, testing the appropriateness of Normal (Gaussian) distribution to two overall data sets by evaluating both the probability plot graphics and the order central moments, we seek day-specific distribution functions in order to analyze the day-to-day variability.…”

“…In a separate paper, we have sought the perfonnance of two models by adopting a traffic flow theory based reconstruction approach [20]. An overall evaluation on freeway travel time reconstruc tion performance of both a macroscopic link perfonnance function based model [21] and a microscopic simulation model, VISSIM [22], is presented considering real data obtained within a case study conducted on a stretch of Istanbul freeway network.…”

“…An overall evaluation on freeway travel time reconstruc tion performance of both a macroscopic link perfonnance function based model [21] and a microscopic simulation model, VISSIM [22], is presented considering real data obtained within a case study conducted on a stretch of Istanbul freeway network. The initial paper [20] presents the simulation results on both day and flow direction basis, those are further considered in the explicit analyses on distributions and reliabilities of model reconstructions in the present paper.…”

“…Reliability of route traversal time distributions specific to modeling approaches are investigated explicitly considering the parameters of approximated func tions. Note that the theories behind modeling methods and the case study conducted for the evaluation of reconstructions are completely excluded in the present paper leaving the reader refer to the initial paper [20].…”