Abstract
Speed has been identified for a long time as a key risk factor in road traffic. Inappropriate speeds contribute to a relevant part of road crashes, and then to the mortality and disabilities resulting from them. Starting from this consideration this paper investigates road safety by analysing operating speed, which is the 85th percentile speed. Particularly, two regression models are proposed to predict operating speeds for different road elements related to specific road conditions. The case study is represented by a two-lane rural highway. Smartphone-equipped vehicles were used to evaluate the operating speed for each element of the analysed road segment. Continuous speed data were recorded by the vehicles driven by users with different driving behaviours. Since the lack of safety is often linked to an inconsistency roadway geometric design, we effected a preliminary quantitative design consistency evaluation that confirmed the need of having accurate experimental measures of operating speed or appropriate models for predicting it. We propose two types of operating speed models: one for estimating speed profiles for horizontal curves, and the other one for tangents. According to both models, operating speed is predicted by the combination of an independent variable representing a geometric characteristic (curve radius for the curves and length for the tangent elements) and an independent variable relating to the speed, and specifically the operating speed of the previous road element. The models show a good predictive capability, and can be considered as a useful tool for operators and technicians for road management.
Highlights
Speed is a key factor in road safety, influencing both the risk of road accidents as well as the severity of the injuries that result from crashes
This paper has presented a road safety study in which safety is investigated by analysing operating speeds on two-lane rural highways
A quantitative design consistency evaluation was performed on a two-way undivided rural highway case study by adopting the methodology proposed by Lamm et al (1999)
Summary
Speed is a key factor in road safety, influencing both the risk of road accidents as well as the severity of the injuries that result from crashes. Geometric road elements (curve and tangent), defined as a function of the design speed, are not in accordance with drivers expectancy, and with their driving behaviour (FHWA 1986). Other authors retain that the lack of speed consistency in the road section is reflected by the large amount of speed differential in the operating speed between the two successive elements along a road (Park, Saccomanno 2006). The knowledge and management of the operating speeds seem to be a crucial point to enhance road safety conditions, because it allows the alignment of the road to be tested as a function of the potential heterogeneity in drivers’ behaviour, as well as to highlight safety issues in the existing roads test of safety conditions (Atashafrazeh, Yadollahi 2013)
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