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Use of Life Cycle Cost Analysis and Multiple Criteria Decision Aid Tools for Designing Road Vertical Profiles
Open AccessArticle

Modeling Impacts of Speed Reduction on Traffic Efficiency on Expressway Uphill Sections

1
School of Highway, Chang’an University, South 2nd Ring Road, Beilin District, Xi’an 710064, China
2
Research Institute of Highway Ministry of Transport, No. 8 Xitucheng Road, Haidian District, Beijing 100088, China
*
Author to whom correspondence should be addressed.
Sustainability 2020, 12(2), 587; https://doi.org/10.3390/su12020587
Received: 9 December 2019 / Revised: 2 January 2020 / Accepted: 11 January 2020 / Published: 13 January 2020
(This article belongs to the Special Issue Road Traffic Engineering and Sustainable Transportation)
Road geometric design is a key factor impacting driving safety and efficiency. In highway profile design, speed reduction is used to determine critical length of grade. Previous research generally concentrated on the relationship between speed reduction and crash involvement rate to establish the recommended value. Limited research results have been reported at this point concerning speed reduction and traffic efficiency. This study aims to fill the gap by investigating tolerable speed reduction with different vertical slopes considering traffic efficiency. Firstly, appropriate experimental sections were determined after field survey. Traffic data including vehicle count, timely speed, vehicle type, and headway time were then collected on an expressway in Shaanxi Province. The associated traffic efficiency was derived from traffic volume and average speed. After this, the modeling between speed reduction and traffic efficiency was processed with different slopes. The correlation between speed reduction and traffic efficiency was therefore verified. Finally, the prediction model of optimum speed reduction concerning traffic efficiency under different vertical slopes was introduced. It was found that the critical length of grade can be longer with traffic efficiency as the major design control incorporated with slopes of 3–3.5%. The existing regulation in critical length of grade at 3.5–5% can benefit both safety and efficiency. The findings can provide a reference for vertical alignment design, leading to high-efficiency road systems. View Full-Text
Keywords: mountainous freeway; speed reduction; traffic efficiency; critical length of grade mountainous freeway; speed reduction; traffic efficiency; critical length of grade
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MDPI and ACS Style

Zhang, X.; Xu, J.; Liang, Q.; Ma, F. Modeling Impacts of Speed Reduction on Traffic Efficiency on Expressway Uphill Sections. Sustainability 2020, 12, 587.

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