During the period from 1988 to 1993 a total of 90,682 injury accidents were reported in the Portuguese main highway network, including more than 73% of which were on two-lane roads outside intersections. Overall, 26% of these accidents occurred on curves. More than 10% of the injury accidents usually occurred at accident black spots totaling less than 1% of the road length. Past attempts to directly relate road characteristics and accidents outside intersections met limited success. Mathematical and conceptual reasons can explain some of these failures. Different factors are known to influence traffic speed: driver population, road characteristics, traffic volume and composition, and prevailing lighting and weather conditions. Some of these factors are also known to be related to accident frequency. With a view to delineate standard procedures to help designers explicitly estimate the impact on safety of their design decisions, the Laboratorio Nacional de Engenharia Civil (LNEC) is presently carrying out a research project on the relations between highway characteristics and accidents using operating speed as a link variable. This paper contains a description of the study, a special emphasis being put on the collection of accident and speed data. Results of a first campaign of speed measurements on curves and tangents of national trunk roads are presented. Geometric characteristics and accident data for these road sections are introduced as well.
Abstract