Flow curves: influence of the different types of users and of the functional classification of the road link

This work is meant to contribute to the experimental study of vehicle traffic on the rural road network. For this purpose, we have considered road arteries characterised both by a commuter flow and an additional tourist flow (peculiar cases of many situations in Sardinia, Italy), that is arteries leading to large towns and links to production areas and to littoral arteries where, in the summer, both typology and volume of traffic changes. Therefore it appears very important to carry out a survey so as to know their state of service and guarantee sufficient safety conditions, also because, besides having different types of vehicles, European, and in particular Italian, users show a very different behaviour compared to American users. On each road, we placed the inductive coil traffic detector on one or more sections. This allowed us to acquire the data necessary to analyse the flow and therefore compare the arteries. We thus studied the conditioning induced by the road geometry and the vehicle flows on the user speed, with the aim of checking the reliability of the numeric assumptions that define the design speed and the levels of service. From the processing, doubts emerged as to the possibility of using the design speed to characterise the entire road, without considering the variability of traffic conditions.