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After a study of the identification of dangerous highway locations in Quebec, the appropriateness of comparisons with U.S. statistics was questioned. It was noted that between 30 and 50 percent of highway accidents in Quebec are associated with harsh meteorological conditions, including rain, snow, hail, and icy conditions, and it was implied that these conditions would contribute to a poorer safety record. To better understand the seasonal variation of highway accidents, monthly numbers and rates of highway accidents of differing severities were examined. The analysis uses all police-reported accidents associated with numbered roads in the Montérégie region of Quebec between 1989 and 1992. Monthly rates of victims per 100 million vehicle km traveled are calculated, as well as the frequency (number) of victims deceased, severely injured, and with minor injuries. Material-damage-only accidents are similarly tabulated. The lowest numbers and rates of death and serious injury occur in winter months. However, accidents with material damage only are most frequent, and have their highest rates, in winter months. Winter is associated with low mortality and serious injury and high numbers and rates of minor accidents. There is a negative correlation between the monthly rankings of injury rates when severe injuries and deaths are compared with material-damage-only accidents. These results underline a point that deserves more attention: conditions associated with mortality and serious injury are in many ways distinct and different from conditions associated with minor injuries and material-damage-only accidents and are poorly, and even negatively in the present example, correlated with these conditions.

Platoon dispersion is a key element in traffic simulation models designed to measure arrivals at traffic signals. One of the most popular models is contained in the TRANSYT program. In this program, dispersion is defined by the platoon dispersion factor, which is given for three types of conditions in relation to external friction. This study demonstrates that platoon dispersion depends not only on external friction but also on internal friction between vehicles in the platoon. As volumes and densities increase, platoon dispersion increases up to a maximum, which is attained at half the capacity. As volumes and densities increase further, dispersion decreases and reaches a minimum value at volumes around maximal capacity. Experimental analysis on eight arterial sites in the city of Montreal (Quebec, Canada) has confirmed this relationship between dispersion and traffic volumes. Mathematical models (having a parabolic shape) relating platoon dispersion to internal and external friction were developed for three different categories of arterial streets representing low, moderate, and heavy friction levels. These models could be introduced into signal coordination programs and could contribute to a better simulation of arriving platoons at intersections as volumes change in relation to time.

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