Abstract: The length of the transition section directly affects the traffic safety at the end of the highway merge area. The regulations on the length of the transition section in JTG D20—2017 Highway Route Design Specification didnt consider the demand when the transition section of the acceleration lane was located in the curved section. And the insufficient length of the transition section located in the curved section may cause the roadside guardrail blocking the drivers line of sight, and there was a safety hazard of insufficient sight distance for parking at the end of the merge. The characteristics of the driving trajectory of the minibus in the transition section at the merge end and the intervisibility conditions for car drivers were analyzed. The hyperbolic tangent lane change model conforming to the actual lane change trajectory was adopted, the transition section meeting the stopping sight distance of the driver of the minibus was taken as the control element, and a parallel acceleration lane transition section length calculation model was constructed for the curve section. Based on the domestic and foreign research and the relevant vehicle operation speed survey data at the merge end, the values of key parameters in the proposed model were determined. Finally, a reasonable length value of parallel acceleration lane transition section on curved roadway was proposed. The study shows that the minimum length of parallel acceleration lane transition section of curved road section is positively correlated with the running speed of minibuses at the merge end, and negatively correlated with the width of hard shoulder and radius of circular curve on the right side of the mainline lane. The minimum length of parallel acceleration lane transition section specified in Highway Route Design Specification can meet the requirement of stopping sight distance when minibuses changing lanes at the merge end when the design speed of mainline is <100 km/h. When the design speed of the mainline is ≥100 km/h, it does not meet the requirement of stopping sight distance when minibuses changing lanes at the merge end, and there is a certain risk of traffic safety. It is recommended to determine the length of the parallel acceleration lane transition section according to the radius of curvature of the mainline and the width of the hard shoulder.

Key words: highway engineering; parallel acceleration lane; length of transition section; parking sight distance; channel change model

摘要： 渐变段长度直接影响高速公路合流区末端的交通安全，JTG D20—2017《公路路线设计规范》中对渐变段长度的规定没有考虑加速车道渐变段位于曲线路段时的需求，位于曲线路段的渐变段长度不足可能导致路侧护栏遮挡驾驶人视线，存在合流末端停车视距不足的安全隐患。分析合流末端渐变段小客车行驶轨迹特点及小车驾驶人的视线通视条件，采用符合实际换道轨迹的双曲正切换道模型，以渐变段满足小车驾驶人停车视距为控制要素，构建了曲线路段平行式加速车道渐变段长度计算模型，并基于国内外研究及相关合流末端车辆运行速度调查数据，确定了该模型中关键参数的取值，最后提出了曲线路段平行式加速车道渐变段合理长度取值。研究表明：曲线路段平行式加速车道渐变段最小长度与合流末端的小客车运行速度正相关，与主线行车道右侧硬路肩宽度和圆曲线半径负相关；JTG D20—2017《公路路线设计规范》规定的平行式加速车道渐变段最小长度能满足主线设计速度＜100 km/h时小客车合流末端换道时停车视距的要求，当主线设计速度≥100 km/h时，不满足小客车合流末端换道时停车视距的要求，存在一定的行车安全风险，建议根据主线曲率半径及硬路肩宽度综合确定平行式加速车道渐变段长度。

关键词: 道路工程；平行式加速车道；渐变段长度；停车视距；换道模型