OPERATING SPEED PREDICTION MODEL AS A TOOL FOR CONSISTENCY BASED GEOMETRIC DESIGN OF FOUR-LANE DIVIDED HIGHWAYS

Gourab Sil,Akhilesh Kumar Maurya,Avijit Maji,Suresh Nama

doi:10.3846/transport.2019.10715

Gourab Sil, Akhilesh Kumar Maurya + Show 2 more

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https://doi.org/10.3846/transport.2019.10715

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Abstract

Researchers have studied two-lane rural highways to predict the operating speed on horizontal curves and correlated it with safety. However, the driving characteristics of four-lane-divided highways are different. Weak lane discipline is observed in these facilities, which influences vehicle speed in adjacent lane or space. So, irrespective of its lane or lateral position, vehicles in four-lane divided highways are considered free flowing only when it maintains the minimum threshold headway from any lead vehicle. Examination of two conditions is proposed to ensure the free flow. Vehicles meeting both conditions, when tracked from the preceding tangent section till the centre of the horizontal curve, are considered as free flowing. The speed data of such free flowing passenger cars at the centre of eighteen horizontal curves on four-lane divided highways is analysed to develop a linear operating speed prediction model. The developed model depends on curve radius and preceding tangent length. The operating speed of passenger car in four-lane divided highways is influenced by horizontal curve of radius 360 m or less. Further, longer tangent would yield higher operating speed at the centre of the curve. Finally, two nomograms are suggested for conventional design, consistency based design and geometric design consistency evaluation of four-lane divided horizontal curves.

Highlights

Vehicle speed depends on driver’s perception of surroundings, which is influenced by highway geometry, traffic control devices, driving environment, weather condition, etc
The operating speed of passenger car in four-lane divided highways is influenced by horizontal curve of radius 360 m or less
Researchers have used the absolute difference between design speed and operating speed to evaluate geometric design consistency and safety of horizontal curves in highways (Lamm et al 1990, 1998)

Summary

Introduction

Vehicle speed depends on driver’s perception of surroundings, which is influenced by highway geometry, traffic control devices, driving environment, weather condition, etc. Researchers have used the absolute difference between design speed and operating speed (i.e., the 85th percentile free flow speed V85) to evaluate geometric design consistency and safety of horizontal curves in highways (Lamm et al 1990, 1998). About 87% of the drivers reduce or maintain their vehicle speed in the horizontal curve while approaching from a tangent section (Bonneson 1999). This means, there are drivers who might have slowed down in the approach tangent for unrelated reasons. They can accelerate in the horizontal curve to attain their preferred speed. In either way drivers tend to maintain safe speed in the curve and this safe speed could be correlated to the horizontal curve geometry such as curve radius

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