Recognition sight distance and minimum radius of vertical curves at expressway tunnel entrances

Authors

• Fu Zhipeng, CCCC First Highway Consultants Co ., Ltd., Xi’an, Shaanxi 710075 , China ;National Key Laboratory of Green and Long-Life Road Engineering in Extreme Environment , Xi’an, Shaanxi 710075 , ChinaFollow
• Zhou Shiyang, Highway School , Chang’an University , Xi’an, Shaanxi 710064 , China
• Pan Binghong, Highway School , Chang’an University , Xi’an, Shaanxi 710064 , ChinaFollow
• Liu Zhi, CCCC First Highway Consultants Co ., Ltd., Xi’an, Shaanxi 710075 , China ;National Key Laboratory of Green and Long-Life Road Engineering in Extreme Environment , Xi’an, Shaanxi 710075 , China
• Liu Yutong, Highway School , Chang’an University , Xi’an, Shaanxi 710064 , China
• Liu Yuying, Highway School , Chang’an University , Xi’an, Shaanxi 710064 , China

Corresponding Author

潘兵宏，男，博士，副教授.E-mail：panbh@chd.edu.cn

Abstract

Lane changing is generally prohibited and strict speed limits are imposed in expressway tunnels in China. To ensure that drivers can safely and comfortably complete lane changes and speed adjustments before entering a tunnel, horizontal curves should satisfy the tunnel entrance recognition sight distance requirement, and the radii of vertical curves in the longitudinal profile should also satisfy this requirement. If the vertical curve radius of the section before a tunnel entrance is improperly designed, drivers may be unable to recognize the tunnel entrance in time, resulting in rushed lane changes or delayed speed adjustments before entering the tunnel, which can easily lead to road traffic accidents caused by improper maneuvers in front of the tunnel entrance. For the purpose of determining the minimum radius of vertical curves required on the approach to a tunnel to satisfy the tunnel entrance recognition sight distance, the tunnel entrance recognition sight distance was first defined according to drivers' operating characteristics and driving needs when selecting lanes and adjusting speeds before entering the tunnel. Second, a vehicle lane-changing model was established using the shifted negative exponential distribution model and the constant-speed offset cosine-curve lane-changing model, and a tunnel entrance recognition sight distance calculation model was constructed. Finally, limiting and normal values for the tunnel entrance recognition sight distance were proposed, and recommended minimum radii of crest and sag vertical curves before the tunnel entrance were proposed based on these values to satisfy the tunnel entrance recognition sight distance. The results show that, when drivers decelerate before the tunnel portal, the minimum radius of the crest vertical curve that satisfies the normal value requirement of the tunnel entrance recognition sight distance is larger than the limiting value of the crest vertical curve stipulated in the Specifications for Highway Geometric Design (JTG D 20—2017). Similarly, the minimum radius of the sag vertical curve that satisfies the normal value requirement of the tunnel entrance recognition sight distance is larger than the normal value of the minimum radius of the sag vertical curve stipulated in the Specifications for Highway Geometric Design (JTG D 20—2017). Therefore, for sections before the entrances of long tunnels, extra-long tunnels, and other tunnels where lane changing is prohibited, the minimum radius of the vertical curve that satisfies the normal value requirement of the tunnel entrance recognition sight distance should be adopted.

Publication Date

8-16-2026

DOI

10.14048/j.issn.1671-2579.2026.04.025

First Page

231

Last Page

242

Submission Date

August 2026

Recommended Citation

Zhipeng, Fu; Shiyang, Zhou; Binghong, Pan; Zhi, Liu; Yutong, Liu; and Yuying, Liu (2026) "Recognition sight distance and minimum radius of vertical curves at expressway tunnel entrances," Journal of China & Foreign Highway: Vol. 46: Iss. 4, Article 25.
DOI: 10.14048/j.issn.1671-2579.2026.04.025
Available at: https://zwgl1980.csust.edu.cn/journal/vol46/iss4/25

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