Operating speed models of two-lane rural state roads developed on continuous speed data

Dražen Cvitanić ,Biljana Maljković

doi:10.17559/tv-20150304133437

Abstract

This paper presents models for predicting operating speeds on tangent sections and curves of two-lane rural roads developed on continuous speed data. The data corresponds to 20 drivers of different ages and driving experiences, driving their own cars along an 18 km long section of a state road. The data were first used for determination of minimum operating speeds on curves and maximum operating speeds on tangents and their comparison with speeds in the middle of curves and tangents i.e. speed data used in most of the operating speed studies. There was no significant difference between speed models developed using speed data in the middle of tangents and curves and models developed using maximum and minimum operating speeds on tangents and curves. Models developed on continuous data have higher coefficient of determination than models developed on spot speed data. It can be concluded that the method of measuring has more significant impact on the quality of speed model than the location of measurement.

Highlights

Examining the accident reports many researches have concluded that one of the main causes of accident occurrence is the lack of geometric design consistency in terms of maintaining the desired travel speeds [1÷7]
The first step in evaluating road design consistency is a development of statistical model that can predict operating speeds based on the geometric characteristics of the alignments elements
The continuous data collected in this study showed that the assumptions that drivers reach their highest speeds in the middle of tangents, or 200 m before the end of tangent, and reach their lowest speeds in the middle of horizontal curves, are not realistic, in general

Summary

Introduction

Examining the accident reports many researches have concluded that one of the main causes of accident occurrence is the lack of geometric design consistency in terms of maintaining the desired travel speeds [1÷7]. The first step in evaluating road design consistency is a development of statistical model that can predict operating speeds based on the geometric characteristics of the alignments elements. The main purpose of this paper is to analyze whether mentioned shortcomings of spot speed measurement and the assumptions of previous operating speed studies like achieving minimum speeds in the middle of the curves and maximum speeds in the middle of tangent sections have impact on the quality of operating speed models. The values of operating speeds V85 determined from the continuous speed data collected on the 18 km long road segment were used for analyzing the locations and values of speeds on curves and tangents relevant to the development of operating speed models. After defining the relevant speeds, the operating speed prediction models for tangent sections were developed based on the geometric characteristics of the road. The locations of minimum curve speed and maximum tangent speed were analyzed

Speeds on curves

Speeds on tangent sections

Operating speed models on tangents

Operating speed models on horizontal curves

Findings

Conclusion