Quantifying the effect of present, past and oncoming alignment on the operating speeds of a two-lane rural road

Filippo Giammaria Praticò,Marinella Giunta

doi:10.3846/bjrbe.2012.25

Filippo Giammaria Praticò, Marinella Giunta

Open Access

https://doi.org/10.3846/bjrbe.2012.25

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Abstract

In the last decades several studies were conducted in order to develop operating speed prediction models for two-lane rural roads. Many factors were found to affect the operating speed, such as radius of horizontal curve or curvature changes rate, grade, length of horizontal curve, deflection angle, sight distance, superelevation rate, side friction factor, and pavement conditions. Though this, many issues arise when there is an appreciable and continuous variance of geometric features along the road and, for example, short and long tangents coexist in the same road. In such conditions, assessing homogeneous sections, calibrating robust algorithms aimed at V85 prediction is a severe task and safety goals are not easily achieved. In the light of the abovementioned facts, objective and scopes of this work were confined into the quantifications of the effect of past, present, and future geometric elements on operating speeds. In particular, attention was focused on the consistency of the assumption of an environmental speed as a reference value for both short (dependent) and long (independent) tangents. Authors proposed a new operating speed model in which the geometric features of the previous and oncoming alignment were explicitly considered. The proposed speed prediction algorithm was validated on the basis of a wide experimental survey carried out in a rural road of the Province of Reggio Calabria – southern Italy. Problem modelling, experimental plan and results discussion are reported. Results proved the validity of the proposed model even if further experiments are needed to make the model able to predict the operating speed in different type of roads.

Highlights

It is well known that vehicle speeds depend on many factors relating to drivers, vehicles, roadway environment, etc. (Kanellaidis 1995)
In the last decades several studies were conducted in order to develop operating speed prediction models for two-lane rural roads (Castro et al 2011; Fitzpatrick et al 2000; Gintalas et al 2008; Krammes et al 1995; Lamm et al 1988; McLean 1981; Misaghi, Hassan 2005, Zuriaga et al 2010)
In particular Polus et al (2000), based on the operating speeds, collected 162 tangent sections of two-lane rural highways, developed a regression model for predicting operating speed on tangents in which the effects of preceding and following horizontal curves are considered. They concluded that on tangent sections the speed of vehicles is dependent on a wide array of roadway characteristics, such as length of the tangent section, radius of the curve before and after the section, cross-section elements, vertical alignment, general terrain, and available sight distance

Summary

Background

It is well known that vehicle speeds depend on many factors relating to drivers, vehicles, roadway environment, etc. (Kanellaidis 1995). In particular Polus et al (2000), based on the operating speeds, collected 162 tangent sections of two-lane rural highways, developed a regression model for predicting operating speed on tangents in which the effects of preceding and following horizontal curves are considered They concluded that on tangent sections the speed of vehicles is dependent on a wide array of roadway characteristics, such as length of the tangent section, radius of the curve before and after the section, cross-section elements, vertical alignment, general terrain, and available sight distance. Krammes et al (1995) assessed the approach speed by means of experimental observations and defined a correlation between the operating speed and several parameters related to the curve, such as the degree of curve, the length, the deflection angle, and the 85th percentile approach speed All these studies demonstrated the importance of considering the conditions of the alignment before or, well again, the overall alignment of the road to better estimate the operating speed in a current horizontal element. Results proved the validity of the proposed model even if further experiments are needed to make the model able to predict the operating speed in different type of roads

Theoretical model and estimation methodology

Experiments and results

Findings

Conclusions