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Left-Side On-Ramp Metering for Improving Safety and Efficiency in Underground Expressway Systems

1
School of Transportation Engineering, Tongji University, 4800 Cao’an Highway, Shanghai 201804, China
2
Key Laboratory of Road and Traffic Engineering of the Ministry of Education, Tongji University, Shanghai 201804, China
*
Author to whom correspondence should be addressed.
Sustainability 2019, 11(12), 3247; https://doi.org/10.3390/su11123247
Received: 1 May 2019 / Revised: 26 May 2019 / Accepted: 4 June 2019 / Published: 12 June 2019
(This article belongs to the Special Issue Sustainable and Intelligent Transportation Systems)
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Abstract

As one of the effective measures of intelligent traffic control, on-ramp metering is often used to improve the traffic efficiency of expressways. Existing on-ramp metering research mainly discusses expressways with right-side on-ramps. However, for underground expressway systems (UESs), left-side on-ramps are frequently adopted to reduce the ground space occupied by ramp construction. Since traffic entering from the left and right sides of the mainline may have different traffic characteristics, on-ramp metering for UESs with left-side on-ramps should be explored specifically. This study examines the impacts of left-side on-ramps on the traffic safety and efficiency of UESs and proposes an effective on-ramp metering strategy. Firstly, using field data, traffic flow fundamental diagrams and speed dispersion are discussed to explore the traffic flow characteristics of the “left-in” UES. The results show that the capacity and critical occupancy are both reduced in left-side on-ramp compared to right-side on-ramp expressways. Meanwhile, the speed dispersion is higher in left-side on-ramp UESs, which means a higher accident risk. Based on this, considering traffic safety and efficiency, a novel two-parameter left-side on-ramp metering strategy for UESs is proposed, in which occupancy and speed are used as the control indicators simultaneously. Additionally, the mechanism of the metering strategy is explained. Finally, the proposed on-ramp metering strategy is simulated on a real UES. The results demonstrate the advantages of the proposed two-parameter on-ramp metering strategy for improving the traffic safety and efficiency of UESs. View Full-Text
Keywords: intelligent transportation systems; traffic safety; urban underground expressway; traffic flow characteristics; left-side on-ramp; ramp metering intelligent transportation systems; traffic safety; urban underground expressway; traffic flow characteristics; left-side on-ramp; ramp metering
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Shao, M.; Xie, C.; Sun, L.; Wan, X.; Chen, Z. Left-Side On-Ramp Metering for Improving Safety and Efficiency in Underground Expressway Systems. Sustainability 2019, 11, 3247.

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