高速公路隧道入口识别视距及竖曲线最小半径研究OA

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 D20-2017).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 D20-2017).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.