Citation

Ferrari P, Cascetta E, Nuzzolo A, Treglia P, Olivotto P. Transp. Res. A Gen. 1984; 18(1): 43-59.

Copyright

(Copyright © 1984, Elsevier Publishing)

DOI

10.1016/0191-2607(84)90093-1

PMID

unavailable

Abstract

The paper presents a method for measuring motorway circulation comfort and safety, based on the determination of the risk and stress levels characterizing the various choices made by drivers on the road. The method was worked out by analysing the distributions of the angular speeds with which the eye of each driver subtends the preceding vehicle width. The data used were taken from 155,000 vehicle passages over two sections of two-lane, divided carriageway motorways of identical geometric characteristics. The analysis suggested that the drivers passing over a motorway section can find themselves in three different states, which we shall term A, B and C, each having its own domain of driving alternatives. State A includes those drivers whose behaviour is not influenced by other vehicles present on the carriageway; state B encompasses those drivers whose behaviour is not influenced by the vehicles preceding them on the same lane, but by those that are following them; state C comprises those whose behaviour is affected by the vehicle preceding them on the same lane. Drivers in state C can be further divided into two groups: those, called C1, who accept the speed of the preceding vehicle and place themselves at a distance from him sufficiently large not to perceive the random fluctaution of relative speed and those, called C2, who do not accept the preceding vehicle speed and, waiting to overtake, approach him at a distance well below that of the C1 drivers so as to prevent the insertion of any changing lane vehicle and, contemporaneously, making their presence felt to the preceding vehicle. Drivers C2 because of the relative speed fluctuations receive a sequence of stimuli to which they react, also unconsciously, with a sequence of accelerations and decelerations. In this way their type of driving is risky and stressing. The authors propose the proportion s of all the drivers not in state C2 to be used as a measure of comfort and safety. The paper discusses and demonstrates how the proportion of drivers in the different states can be estimated; it also investigates the relationship existing between the measure s and the flow rate Q for various flow and time of day conditions. Furthermore the quality of circulation measure [xi]1 defined by the same authors in a preceding paper is shown to be strongly correlated with s.