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241.
从广域运输管理、进路控制、列车控制和通信系统4个方面,介绍了欧洲铁路通信信号系统的技术现状和发展。 相似文献
242.
Abolition of the National Dock labour Scheme in July 1989 has intensified competition in Britian's ports and allowed the major port authorities and other port operators to restructure their operations and develop new investment plans. But the result has been to add to excess capacity in the industry and to porduce a 'zero-sum' process of traffic redistribution between Britain's driven largely by customer demands for lower charges. 相似文献
243.
244.
Peter Bonsall 《Transportation》1976,5(3):309-329
This paper highlights some of the difficulties involved in the implementation of complex cost structures in the tree-building section of a transport demand model. The conventional tree-building algorithm is briefly described and is seen to be inadequate for the present purpose. A new algorithm is then presented which is able to implement complex cost structures properly. An example is given of the application of this algorithm to the building of tree in a public transport network. The performance of a computer program incorporating the new alrogrithm is evaluated against alternative methods of implementing complex cost structures. Some mention is then made of the vast range of potential uses for the new algorithm in the field of transport modelling and simulation. 相似文献
245.
Modeling and Analysis of Automotive Antilock Brake Systems Subject to Vehicle Payload Shifting 总被引:4,自引:0,他引:4
Val Mills Bernard Samuel John Wagner 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2002,37(4):283-310
The steerability and stability of vehicles must be maintained during emergency stopping and evasive driving maneuvers on degraded road surfaces. The introduction of antilock brake and traction control systems (ABS/TCS) has expanded the envelope of safe vehicle operation for the majority of drivers. These mechatronic systems combine an electronic controller with wheel speed sensors, an electro-mechanical hydraulic brake actuator, and in some instances, engine intervention through the engine control unit, to regulate wheel slip. The development of ABS systems has traditionally depended on extensive in-vehicle testing, at cold weather proving grounds, which contribute to lengthy product development cycles. However, recent attention has been focused on the use of simulation and hardware-in-the-loop strategies to emulate test conditions in a controlled setting to shorten product design time and methodically address critical safety issues. In this paper, the effect of transient load shifting due to cargo movement on ABS performance in light-duty vehicles will be investigated. Analytical and empirical mathematical models are presented to describe the chassis, tire/road interface, wheel, brake modulator, and cargo dynamics. Two strategies, a model-free table lookup and model-based discrete nonlinear controller, are presented to regulate the ABS modulator's operation. These vehicle and controller dynamics have been integrated into a simulation tool to investigate the effect of transient weight transfers on the vehicle's overall stopping distance and time. Representative numerical results are presented and discussed to quantify the ABS systems' performance for various loading and operating conditions. 相似文献
246.
Sven T. H. Jansen Peter W. A. Zegelaar Hans B. Pacejka 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1999,32(2):249-261
For efficient analysis it is important to choose the proper model that fits the problem that needs to be solved. This paper discusses three pragmatic simulation models for longitudinal behaviour of a passenger car tyre (Steady State, Transient and Rigid Ring) that may be used in e.g. an ABS simulation. The characteristics of the simulation models are evaluated using some simple simulations. Simulations with a quarter vehicle model that includes load transfer effects are carried out to determine the deviation in results between the mentioned tyre models for an ABS application. The results show that the Steady State model may only be used below 10 Hz and that the Transient model is valid up to about 30 Hz. The results from the ABS simulation with the Rigid Ring model are most reliable and are clearly different from the Steady State and Transient model, which indicates that ABS simulations should be carried out with the Rigid Ring model. Additionally it is demonstrated that for tyre behaviour on uneven roads the influence of the tyre belt cannot be neglected. 相似文献
247.
Peter R. White 《Transportation》1978,7(2):225-242
This paper reviews the present levels of operating support to, and public investment in, public transport systems in Western Europe. All internal bus, tram and rail services are included, and estimates made for total support in Britain, Sweden, West Germany, the Netherlands and France. To make comparison meaningful, these are shown in relation to GDP and traffic carried. Support levels in Britain are below average, but by no means the lowest as sometimes assumed. Reasons for providing support are considered, including existence of financial burdens arising historically, assistance to particular groups of users, problems in price discrimination and inability of other modes' charges to reflect costs. The extent to which support payments may merely subsidise inefficiency is outlined. A distinction is drawn between productive efficiency, i.e. the resources used to provide a specified level of service and fare, and allocative efficiency, i.e. the extent to which resources are allocated so as to maximise traffic, etc. The extent for reducing support yet retaining the present general level of service and fare is considered.Means of raising finance for support are outlined, including relative roles of central and local government. The scope of local taxes being raised to meet local objectives is considered, notably in the French versement transport: In conclusion, it is suggested that trunk inter-city services should cover all costs from fares, by a discriminatory pricing policy, but central government provide a basic support level for rural areas. In urban areas, practical limits exist to price discrimination, and the best policy may be collective purchase of facilities through a local tax. 相似文献
248.
Peter Múčka 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2016,54(12):1651-1670
This study is aimed quantify dissipated power in a damper of automobile suspension to predict energy harvesting potential of a passenger car more accurately. Field measurements of power dissipation in a regenerative damper are still rare. The novelty is in using the broad database of real road profiles, a 9 degrees-of-freedom full-car model with real parameters, and a tyre-enveloping contact model. Results were presented as a function of road surface type, velocity and road roughness characterised by International Roughness Index. Results were calculated for 1600 test sections of a total length about 253.5?km. Root mean square of a dissipated power was calculated from 19 to 46?W for all four suspension dampers and velocity 60?km/h and from 24 to 58?W for velocity 90?km/h. Results were compared for a full-car model with a tyre-enveloping road contact, full-car and quarter-car models with a tyre–road point contact. Mean difference among three models in calculated power was a few per cent. 相似文献
249.
Recent advances in communication and computing technology have made travel time measurements more available than ever before. In urban signalized arterials, travel times are strongly influenced by traffic signals. This study presents a novel method based on well‐known principles to estimate traffic signal performance (or more precisely their major “through” movements) based on travel time measurements. The travel times were collected between signals in the field by using point‐to‐point travel time measurement technologies. Closed‐circuit television cameras and signal databases were used to collect traffic demand and signal timings, respectively. Then, the volume/capacity ratio of major downstream signal movements was computed based on demand and signal timings. This volume/capacity ratio was then correlated with travel times on the relevant intersection approach. The best volume‐delay function was found, along with many other functions, to fit the field data. This volume‐delay function was then used to estimate volume/capacity ratios and, indirectly, a few other signal performance metrics. The method, called travel time‐based signal performance measurements, was automated and displayed on a Google Map. The findings show that the proposed method is accurate and robust enough to provide necessary information about signal performance. A newly developed volume‐delay function was found to work just slightly better than the Bureau of Public Roads curve. Several issues, which may reduce the accuracy of the proposed method, are identified, and their solutions are proposed for future research. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
250.
Simon Peter Shepherd 《Transportation》2008,35(4):559-577
Transport externalities such as costs of emissions and accidents are increasingly being used within appraisal and optimisation
frameworks alongside the more traditional congestion analysis to set optimal transport policies. Models of externalities and
costs of externalities may be implemented by a simple constant cost per vehicle-km approach or by more complex flow and speed
dependent approaches. This paper investigates the impact of using both simple and more complex models of CO2 emissions and cost of accidents on the optimal toll for car use and upon resulting welfare levels. The approach adopted is
to use a single link model with a technical approach to the representation of the speed-flow relationship as this reflects
common modelling practice. It is shown that using a more complex model of CO2 emitted increases the optimal toll significantly compared to using a fixed cost approach while reducing CO2 emitted only marginally. A number of accident models are used and the impact on tolls is shown to depend upon the assumptions
made. Where speed effects are included in the accident model, accident costs can increase compared to the no toll equilibrium
and so tolls should in this case be reduced compared to the congestion optimal toll. Finally it is shown that the effect of
adding variable CO2 emission models along with a fixed cost per vehicle-km for accidents can increase the optimal toll by 44% while increasing
the true welfare gained by only 8%. The results clearly demonstrate that model assumptions for externalities can have a significant
impact on the resulting policies and in the case of accidents the policies can be reversed.
Simon Peter Shepherd at the Institute for Transport Studies since 1989, he gained his doctorate in 1994 applying state-space methods to the problem of traffic responsive signal control in over-saturated conditions. His expertise lies in modelling and policy optimisation ranging from detailed simulation models through assignment to strategic land use transport models. He is currently working on optimal cordon design and systems dynamics approaches to strategic modelling. 相似文献
Simon Peter ShepherdEmail: |
Simon Peter Shepherd at the Institute for Transport Studies since 1989, he gained his doctorate in 1994 applying state-space methods to the problem of traffic responsive signal control in over-saturated conditions. His expertise lies in modelling and policy optimisation ranging from detailed simulation models through assignment to strategic land use transport models. He is currently working on optimal cordon design and systems dynamics approaches to strategic modelling. 相似文献