Penn State University, 201 Transportation Research Building, University Park, PA 16802, USA.
Mechanical Engineering, Penn State University, 157D Hammond Building, University Park, PA 16802, USA.
J Safety Res. 2014 Jun;49:105-12. doi: 10.1016/j.jsr.2014.03.005. Epub 2014 Apr 24.
This paper presents the results of a comprehensive project whose goal is to identify roadway design practices that maximize the margin of safety between the friction supply and friction demand. This study is motivated by the concern for increased accident rates on curves with steep downgrades, geometries that contain features that interact in all three dimensions - planar curves, grade, and superelevation. This complexity makes the prediction of vehicle skidding quite difficult, particularly for simple simulation models that have historically been used for road geometry design guidance.
To obtain estimates of friction margin, this study considers a range of vehicle models, including: a point-mass model used by the American Association of State Highway Transportation Officials (AASHTO) design policy, a steady-state "bicycle model" formulation that considers only per-axle forces, a transient formulation of the bicycle model commonly used in vehicle stability control systems, and finally, a full multi-body simulation (CarSim and TruckSim) regularly used in the automotive industry for high-fidelity vehicle behavior prediction. The presence of skidding--the friction demand exceeding supply--was calculated for each model considering a wide range of vehicles and road situations.
The results indicate that the most complicated vehicle models are generally unnecessary for predicting skidding events. However, there are specific maneuvers, namely braking events within lane changes and curves, which consistently predict the worst-case friction margins across all models. This suggests that any vehicle model used for roadway safety analysis should include the effects of combined cornering and braking.
The point-mass model typically used by highway design professionals may not be appropriate to predict vehicle behavior on high-speed curves during braking in low-friction situations. However, engineers can use the results of this study to help select the appropriate vehicle dynamic model complexity to use in the highway design process.
本文介绍了一个综合性项目的研究结果，该项目旨在确定最大程度地提高摩擦供应与需求之间安全裕度的道路设计实践。本研究的动机是关注曲线带有陡坡的弯道处事故率增加，这些几何形状包含在所有三个维度上相互作用的特征 - 平面曲线、坡度和超高。这种复杂性使得车辆滑转的预测变得非常困难，特别是对于历史上一直用于道路几何设计指导的简单模拟模型。
为了获得摩擦裕度的估计值，本研究考虑了一系列车辆模型，包括：美国州际公路运输官员协会（AASHTO）设计政策使用的质点模型、仅考虑每轴力的稳态“自行车模型”公式、车辆稳定性控制系统中常用的自行车模型的瞬态公式，最后是汽车行业中用于高保真车辆行为预测的全多体模拟（CarSim 和 TruckSim）。对于每种模型，考虑了广泛的车辆和道路情况，计算了摩擦需求超过供应的滑转情况。
结果表明，对于预测滑转事件，最复杂的车辆模型通常是不必要的。然而，有一些特定的操作，即在车道变换和曲线内的制动事件，始终在所有模型中预测最差摩擦裕度。这表明，任何用于道路安全分析的车辆模型都应包括转弯和制动的综合效果。
高速公路设计专业人员通常使用的质点模型可能不适用于预测低摩擦情况下高速曲线制动时的车辆行为。然而，工程师可以使用本研究的结果来帮助选择在高速公路设计过程中使用的适当车辆动力学模型复杂性。
