Effect of Grade on Operating Speed and Capacity of Two-Lane Rural Roads
Publication: Journal of Transportation Engineering, Part A: Systems
Volume 149, Issue 7
Abstract
Two-lane rural roads constitute a significant part of the roadway system in India. Geometric characteristics such as facility type, lane width, shoulder width, and horizontal and vertical alignments, are essential parameters that influence vehicle behavior and traffic flow characteristics on two-lane rural roads. Among all geometric characteristics, the magnitude of the grade most substantially impacts the operational characteristics of traffic flow on two-lane rural roads. The present study investigates the effect of grade on the operating speed and capacity of two-lane rural roads under mixed traffic conditions. Traffic video data for eight road sections with grades varying from 1% to 8% were collected under dry weather conditions. The investigation revealed a significant effect of grade on the operating speeds of different vehicle types. The operating speed decreased with an increase in the grade magnitude. The road capacity was derived by calibrating various single regime models. The Northwestern model was deemed appropriate to derive the capacity values, based on theoretical and statistical investigation. The results showed that the capacity decreases by 6.4% with every 1% increase in grade. Further, the effect of grade on passenger car units (PCU) of different vehicle types was investigated. For varying volume-to-capacity (V/C) ratios, it was observed that the PCU of heavy vehicles increases as the magnitude of the grade increases. The present study develops operating speed and capacity prediction models as an essential practical outcome. The developed models can facilitate planners and traffic engineers to estimate operating speed and capacity based on the magnitude of the grade.
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Data Availability Statement
Some or all data, models, or codes generated or used during the study are available from the corresponding author by request. The density, speed, flow, and operating speed for certain sections will be made available upon reasonable request.
Acknowledgments
Author Contributions: The authors confirm contribution to the paper as follows: study conception and design: Jain, Gore, Arkatkar, and Easa; data collection: Jain, Arkatkar; analysis and interpretation of results: Jain, Gore, Arkatkar, and Easa; and draft manuscript preparation: Jain, Gore, Arkatkar, and Easa. All authors reviewed the results and approved the final version of the manuscript.
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Journal of Transportation Engineering, Part A: Systems
Volume 149 • Issue 7 • July 2023
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© 2023 American Society of Civil Engineers.
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Received: May 9, 2022
Accepted: Dec 14, 2022
Published online: Apr 18, 2023
Published in print: Jul 1, 2023
Discussion open until: Sep 18, 2023
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