Optimization-based assisted calibration of traffic simulation models

Use of traffic simulation has increased in recent decades; and this high-fidelity modelling, along with moving vehicle animation, has allowed transportation decisions to be made with better confidence. During this time, traffic engineers have been encouraged to embrace the process of calibration, in which steps are taken to reconcile simulated and field-observed performance. According to international surveys, experts, and conventional wisdom, existing (non-automated) methods of calibration have been difficult or inadequate. There has been extensive research on improved calibration methods, but many of these efforts have not produced the flexibility and practicality required by real-world engineers. With this in mind, a patent-pending (US 61/859,819) architecture for software-assisted calibration was developed to maximize practicality, flexibility, and ease-of-use. This architecture is called SASCO (i.e. Sensitivity Analysis, Self-Calibration, and Optimization). The original optimization method within SASCO was based on “directed brute force” (DBF) searching; performing exhaustive evaluation of alternatives in a discrete, user-defined search space. Simultaneous Perturbation Stochastic Approximation (SPSA) has also gained favor as an efficient method for optimizing computationally expensive, “black-box” traffic simulations, and was also implemented within SASCO. This paper uses synthetic and real-world case studies to assess the qualities of DBF and SPSA, so they can be applied in the right situations. SPSA was found to be the fastest method, which is important when calibrating numerous inputs, but DBF was more reliable. Additionally DBF was better than SPSA for sensitivity analysis, and for calibrating complex inputs. Regardless of which optimization method is selected, the SASCO architecture appears to offer a new and practice-ready level of calibration efficiency.     

An enhanced SPSA algorithm for the calibration of Dynamic Traffic Assignment models

Simultaneous perturbation stochastic approximation (SPSA) is an efficient and well established optimization method that approximates gradients from successive objective function evaluations. It is especially attractive for high-dimensional problems and has been successfully applied to the calibration of Dynamic Traffic Assignment (DTA) models. This paper presents an enhanced SPSA algorithm, called Weighted SPSA (W-SPSA), which incorporates the information of spatial and temporal correlation in a traffic network to limit the impact of noise and improve convergence and robustness. W-SPSA appears to outperform the original SPSA algorithm by reducing the noise generated by uncorrelated measurements in the gradient approximation, especially for DTA models of sparsely correlated large-scale networks and a large number of time intervals. Comparisons between SPSA and W-SPSA have been performed through rigorous synthetic tests and the application of W-SPSA for the calibration of real world DTA networks is demonstrated with a case study of the entire expressway network in Singapore.     

A pattern recognition algorithm for assessing trajectory completeness

Vehicular trajectories are widely used for car-following (CF) model calibration and validation, as they embody characteristics of individual driving behaviour (each trajectory reflects an individual driver). Previous studies have highlighted that the trajectories should contain all the major vehicular interactions (driving regimes) between the leader and the follower for reliable CF model calibration and validation. Based on Dynamic Time Warping and Bottom-Up algorithms, this paper develops a pattern recognition algorithm for vehicle trajectories (PRAVT) to objectively, accurately, and automatically differentiate different driving regimes in a trajectory and then select the most complete trajectories (i.e. trajectories containing a maximum number of regimes). PRAVT is rigorously tested using synthetic data and then applied to the NGSIM data. We have observed that the NGSIM data are dominated by the trajectories which contain only three regimes, namely acceleration, deceleration, and following, 77% of the trajectories lack the standstill regime, and no trajectory in the NGSIM data is complete. These findings’ impact on how to properly utilize NGSIM data can be profound. Given the extensive use of the NGSIM data in the traffic flow community, this paper also provides insights about the types of regimes contained in each trajectory of the NGSIM data.     

A macroscopic loading model for time-varying pedestrian flows in public walking areas

A macroscopic loading model applicable to time-dependent and congested pedestrian flows in public walking areas is proposed. Building on the continuum theory of pedestrian flows and the cell transmission model for car traffic, an isotropic framework is developed that can describe the simultaneous and potentially conflicting propagation of multiple pedestrian groups. The model is formulated at the aggregate level and thus computationally cheap, which is advantageous for studying large-scale problems. A detailed analysis of several basic flow patterns including counter- and cross flows, as well as two generic scenarios involving a corner- and a bottleneck flow is carried out. Various behavioral patterns ranging from disciplined queueing to impatient jostling can be realistically reproduced. Following a systematic model calibration, two case studies involving a Swiss railway station and a Dutch bottleneck flow experiment are presented. A comparison with the social force model and pedestrian tracking data shows a good performance of the proposed model with respect to predictions of travel time and density.     

沪通铁路土压力盒标定工装设计及试验研究

为获取精确的测试数据,提出土压力盒标定需求,通过ANSYS建模分析,设计适用于试验室土压力盒的标定工装:承压板直径取32 cm,标定桶高15 cm,内径33 cm,承压板板厚2 cm,标定桶壁厚0.5 cm。并进行了试验研究,试验表明:采用最小二乘法线性拟合获得的相关系数R~2均大于0.99,线性较好,且同一量程下的2个土压力盒的砂标K_1与厂标K_2的比值相近,数据重复性较好,工装合理适用;砂标K_1大于厂标K_2,工程应用之前,结合工程实际进行标定是必要的;量程选取时,使用范围不宜超过土压力盒最大量程的2/3。     

EGR系统在SNH4102型柴油机中的标定试验

EGR系统是治理内燃机排放污染物Nq的有效方法之一,在PTO台架上对SNH4102型柴油机EGR系统进行标定试验,采用真空度控制EGR阀开度,实现EGR系统的调节。在柴油机额定转速下,将测功器开至100％,75％,50％,10％;在最大扭矩下,将测功器开至100％,75％,50％;及怠速工况下,找到EGR阀最佳开度,完成EGR系统的标定;并通过NHA-501型废气分析仪和FLB-100不透光式烟度计等测量排放物的含量。结果表明：在SNH4102型柴油机台架试验中,EGR系统对于NOx的控制有明显的效果,对CO和HC等排放物的抑制作用不明显。     

工况分析法试验在汽油发动机管理系统匹配标定过程中的应用研究

本文对工况分析法试验进行了定义，论述了该试验在匹配标定过程中的作用，介绍了该试验中的工况统计分析法和过程分析法在十五工况排放试验，底盘测功机的十五工况油耗和等速油耗试验，试验场整车道路试验，城区道路试验中的应用。     

2DIR-TRACC传感器校准研究

碰撞假人用位移传感器用来测量碰撞过程中假人膝部、胸部等部位产生的位移量,以此判断碰撞对人体的伤害程度,本文详述了2DIR-TRACC传感器线位移灵敏度、横向位移量、旋转电位计灵敏度的校准方法,运用最小二乘法拟合及单变量求解得到了传感器灵敏度的最优解,并评定了2D IR-TRACC传感器线位移测量结果的测量不确定度,验证...     

锥体铁路罐车容积检定方法的研究

根据锥体铁路罐车的结构特点,研究锥体铁路罐车容积计算方法、检定方法,采用"铁路罐车容积量传系统"对检定方法进行试验验证,确定了新型锥体铁路罐车容积检定、容积表编制方法。     

铁道车辆轮重测定仪检定装置的研制

为满足铁路货场铁路车辆轮重测定仪的现场检测与维修工作,研制了体积小、重量轻、结构简单的LJ-B型铁路车辆轮重测定仪检定装置。从研制目标、系统结构与原理、研制方案和技术难点及实际运用情况等方面,详细介绍LJ-B型铁路车辆轮重测定仪检定装置。