Improved Speed Estimation From Single-Loop Detectors With High Truck Flow

Single-loop detectors are the most common sensors employed by freeway traffic management agencies. The data are used for traffic management and traveler information. Single-loop detectors can only measure flow and occupancy. Although speed is often the most useful metric, it can only be estimated at conventional single-loop detectors. Typically this estimate comes from the quotient of flow and occupancy multiplied by the fixed, assumed average effective vehicle length. This conventional approach is limited because the actual average effective vehicle length will vary from sample to sample. Many researchers have proposed alternatives to address this problem, and although many of the methods work well under normal conditions, there has been limited research into methods that yield reliable estimates under heavy truck traffic. Heavy truck flows may arise as a function of location or time of day, for example, with proximity to a trucking facility or in early mornings when the number of passenger vehicles drops, respectively. This article presents a new methodology to estimate speed from single-loop detectors in conditions where trucks comprise a large percentage of the fleet. While the focus is on single loop detectors, the work is equally applicable to side-fire microwave radar detectors that emulate single-loop detectors.     

雾天高速公路限速模型研究

文章通过对传统的基于停车视距和基于交通标志视认距离的雾天高速公路限速模型的分析,提出了考虑比较全面的组合限速模型,并采用保守分析与乐观分析方法对各种限速模型的计算结果进行比较,论证各种限速模型的特点和适用条件,同时还提出了不同能见度条件下的高速公路限速值和管理措施,为高速公路雾天行车安全管理提供借鉴。     

船用低速柴油机实时仿真模型开发及应用

以某型小缸径船用低速柴油机为对象,基于该柴油机一维性能模型,开展实时仿真模型的快速开发和标定。比较了简化后实时仿真模型与原性能模型的计算时间和仿真精度。应用该模型在硬件在环测试平台上测试新研制的柴油机控制器。试验结果表明,该模型可正常接收和反馈正确的控制器指令和柴油机运行参数,满足电控系统硬件在环测试的试验要求。     

编组站尾部停车监控系统的发展与未来

针对编组站尾部作业压力大、事故隐患多等问题,本文阐述了在编组站自动调速系统中应用尾部监控系统的重要性和必要性,简单介绍了系统发展经历的阶段和实施步骤,概括说明了系统的组成结构及主要功能,同时展望了监控系统未来的发展以及其在编尾调速自动化和尾部安全作业生产应用中的广阔发展前景。     

Speed limit laws in America: The role of geography, mobility and ideology

Speed limits had been centralized at the federal level since 1974, until decisions were devolved to the states in 1995. However, the centralization debate has reemerged in recent years. This paper conducts the first econometric analysis of the determinants of speed limit laws and State reactions after the repeal. By using mobility, geographic and political variables, our results suggest that geography - which reflects private mobility needs and social preferences -, is one of the main factors influencing speed limit laws, together with political ideology. Furthermore, we identify the presence of regional and time diffusion effects. By presenting first evidence on policy determinants, we provide a better understanding of the formulation of the heterogeneity of speed limits in US and offer implications for the debate on centralization and decentralization of transport policy.