Probe vehicle sample sizes for travel time estimation on equipped motorways

This paper presents the dimensioning of a fleet of probe vehicles on motorways equipped with fixed measuring stations. The interurban network concerned, managed by ASF Company, is well adapted to such an analysis. It is equipped with a high density of double loops stations, making it possible to estimate travel times on various sections of the network with an acceptable accuracy. The site and the characteristics of the data collection system are described. Thereafter, an algorithm of calculation of the travel time is developed and validated. It is based on the measurements provided by the loop sensors located on the road section links. A database of travel times -considered as travel times of reference-is thus made up. It provides knowledge on the statistical indicators of the travel time. The sample sizes of probe vehicles can then be determined. Traffic states are taken into account through a preliminary segmentation in levels of service. A sensitivity analysis of the main factors influencing the size of the samples is carried out while the limits of the exercise are also identified. Conclusions include a comparison between the probe vehicles approach and the traditional practices in road traffic management.