The reliability of using the gravity model for forecasting trip distribution

The main purpose of this study is to assess the forecasting capability of the gravity model and to investigate the merit of including K-factors when using the model. Peak hour trip data was obtained for four study year periods 1962, 1971, 1976 and 1981 for the City of Winnipeg. Analysis of the calibration results indicated that the F-factors for the twenty year period were stable within a range of values. In general, however, the K-factors were found to be inconsistent from one prediction period to the next, and when used in forecasting trips they resulted in larger errors than without their use. The validity of using K-factors or the method which has been used to determine them is questionable. It was concluded that while K-factors are very meaningful in theory (as defined), they are not appropriate for use in predicting O-D matrices based on the method by which they are currently estimated (i.e. as a simple ratio). Further study is needed to investigate an alternative method of calibrating the gravity model such as the cell-by-cell regression method.     

Chlorophyll estimation in the Southeastern Mediterranean using CZCS images: adaptation of an algorithm and its validation

Region-specific algorithm to derive chlorophyll concentration from Coastal Zone Color Scanner (CZCS) images was adopted following field measurements in the Southeastern Mediterranean Sea, in June 1992. Reflectance in the range 400 to 700 nm, chlorophyll concentration and seston dry weight were measured simultaneously at 21 stations. The optical model used based on algorithm for Case I waters, using shipboard simulation of CZCS channels for adaptation of parameters. The resulting model was validated with an independent data sets from series of cruises in the Southeastern Mediterranean (1981–1984). Concurrent CZCS images were used for retrieval of the radiance ratio Channel 1/Channel 3, for each station. The resulting ratios were then used to calculate chlorophyll concentrations. A comparison between those calculated concentrations and the actual chlorophyll measurements showed that an estimation error of chlorophyll as low as 0.013 mg m⁻³ was achieved.     

Theoretical Analysis of the Steering Behaviour of Articulated Frame Steer Vehicles

A theoretical analysis of the steering behaviour of articulated frame steer vehicles is presented. It includes details of the hydraulic steering system as well as the equations governing motion of the front and rear body units. Both oscillatory and exponential instabilities can occur with this type of vehicle. The most sensitive design feature is the steering system, which governs the effective torsional stiffness around the pivot. Other important features which influence stability are speed and centre of gravity positions of the bodies.     

A Variable Free Control Characteristic Vehicle

A variable characteristic car (VCC) has been developed at Melbourne University for driverlvehicle handling research. The vehicle is unusual in that it has facilities for varying both its fixed control and free control dynamic characteristics over wide ranges. In this paper the servo systems used to effect these changes are described. The calibration methods used to relate the vehicle response characteristics to the variable servo settings are detailed. Sample calibration results are given for the fixed control parameters steering ratio, yaw response time and stability factor. Calibration of the free control parameters is also described and results are given for the steering torque gradient, and the time-to-peak and percentage overshoot of the steering wheel motion in response to a step input of torque.     

Road profile input estimation in vehicle dynamics simulation

Vehicle motion simulation accuracy, such as in accident reconstruction or vehicle controllability analysis on real roads, can be obtained only if valid road profile and tire-road friction models are available. Regarding road profiles, a new method based on sliding mode observers has been developed and is compared with two inertial methods. Experimental results are shown and discussed to evaluate the robustness of our approach.     

A continuum model for the dispersion of traffic on two-lane roads

A continuum model for two-lane traffic flow is developed using the theory of kinematic waves in which the wavespeeds in the two lanes are assumed constant but unequal. The transient behaviour is found exactly using Riemann's method of characteristics and an asymptotic model of the long time flow is described. It is shown, that for large times, the traffic concentration moves with a weighted mean wavespeed of the two lanes and disperses about this mean speed as a result of interlane concentration differences generated by the relative wavespeeds. The dispersion can be described by a virtual coefficient of diffusion proportional to the square of the differences of the two wavespeeds and inversely proportional to the rate of lane changing. The technique is extended to describe three-lane traffic flow and to include the dependence of wavespeed upon concentration.     

我国农村物流网络节点体系发展思路

为服务乡村振兴战略实施、深入贯彻落实“四好农村路”建设精神，及时了解新时期我国农村物流网络体系的发展现状，探索农村物流网络节点建设的发展对策，通过实地调研、问卷调查、文献调查等调查方法以及指标对比分析法、分组分析法等统计方法，对农村物流网络节点的数量、分布规律及特点等进行了分析，对农村物流运输组织模式类别进行了划分，并总结了各模式下农村物流网络节点的特点。在此基础上，提出我国下一步推进农村物流网络节点发展的思路，认为构建我国农村物流网络节点体系应注重因地制宜，坚持“建管运”并举，促进物流服务与产业发展协同联动。     

城市轨道交通网络的结构及规划理念

创建一个等级划分明确、编织质量良好的城市轨道交通线网,对城市活动和功能的发挥将呈现出巨大的支撑作用,对优化城市用地空间将起到积极的引导作用.多种交通模式相互衔接的大型换乘枢纽具有对轨道交通线网骨架和城市发展的"锚固"作用.针对目前中国各大城市机动化大发展、小汽车使用迅猛增长、城市道路交通严重拥堵和环境污染日益严重的局面,确立中远期轨道交通在整个综合交通系统中的骨干和主导地位意义深远.