A computation method on time-dependent accessibility of urban rail transit networks for the last service

Urban rail transit networks seldom provide 24-hour service. The last train is the latest chance for passengers. If passengers arrive too late to catch the last train, the path becomes inaccessible. The network accessibility thus varies depending on the departure time of passenger trips. This paper focuses on the computation method on the time-dependent accessibility of urban rail transit networks in order to facilitate the itinerary planning of passengers. A label setting algorithm is first designed to calculate the latest possible times for Origin–Destination (O–D) pairs, which is the latest departure times of passengers from the origins such that the destinations can be reach successfully. A searching approach is then developed to find the shortest accessible path at any possible departure times. The method is applied in a real-world metro network. The results show that the method is a powerful tool in solving the service accessibility problem. It has the ability to allow passengers to plan an optimal itinerary. Comparison analysis indicates that the proposed method can provide exact solutions in much shorter time, compared with a path enumeration method. Extensive tests on a set of random networks indicate that the method is efficient enough in practical applications. The execution time for an O–D pair on a personal computer with 2.8 GHZ CPU and 4GB of RAM is only 1.2 s for urban rail transit networks with 100 transfer stations

SUSTAINABILITY ASSESSMENT OF SPEED REGULATION OF URBAN TRAFFIC

Speed regulation of motor vehicles has widely affected the living environment and standard of residents in urban areas. It is believed that lower speed of motor vehicles could decrease the traffic accident rate on roads. However, lower speeds may cause many problems indirectly to social development and the health of residents. The average speed of motor vehicles in urban areas in China may be among the lowest in the world due to its mixed traffic environment and vehicle properties. In most central areas of large Chinese cities, the average speed of motor vehicles has been lower than 25km/h. However, this does not mean a safer system for transportation. For example, the death toll of transportation systems in China has exceeded 70,000 every year and is among the highest in the world. This paper analyses the general situation of various speed regulations on motor vehicles in China. A brief review on the relationship between speed and safety on urban transport has been described. Authors believe that the most important factor to menace transport safety is the coordination of motor vehicles with bicycles and pedestrians especially in urban areas. A quantitative assessment on indirect effects of speed regulation has then been discussed. The assessment covers four aspects. Firstly, it estimates the additional emissions resulted from speed regulation. Secondly, it calculates the contribution to road traffic density of extra stay of vehicles caused by speed change. Thirdly, it analyses the change of passenger journey time caused by speed regulation in urban areas. Finally, the paper calculates the energy consumption of vehicles related to speed regulation. The paper also discusses the policy on speed regulation from viewpoint of sustainable development of urban society. It concludes that higher speed of motor vehicles is of better sustainability in the current situation of Chinese urban areas. Some suggestions on speed regulation for different situations in China have also been presented. The research has been part of the project funded by the Natural Science Foundation of China (No. 70173014) and the Royal Society of UK

A general-purpose simulator for train operations

Computer simulation has been widely accepted as an essential tool for the analysis of many engineering systems. It is nowadays perceived to be the most readily available and feasible means of evaluating operations in real railway systems. Based on practical experience and theoretical models developed in various applications, this paper describes the design of a general-purpose simulation system for train operations. Its prime objective is to provide a single comprehensive computer-aided engineering tool for most studies on railway operations so that various aspects of the railway systems with different operation characteristics can be investigated and analysed in depth. This system consists of three levels of simulation. The first is a single-train simulator calculating the running time of a train between specific points under different track geometry and traction conditions. The second is a dual-train simulator which is to find the minimum headway between two trains under different movement constraints, such as signalling systems. The third is a whole-system multi-train simulator which carries out process simulation of the real operation of a railway system according to a practical or planned train schedule or headway; and produces an overall evaluation of system performance

Modeling circulation of train-set with multiple routing

Planning on utilization of train-set is one of the key tasks of transport organization for passenger dedicated railway in China. It also has strong relationships with timetable scheduling and operation plans at a station. To execute such a task in a railway hub pooling multiple railway lines, the characteristics of multiple routing for train-set is discussed in term of semicircle of train-sets' turnover. In programming the described problem, the minimum dwell time is selected as the objectives with special derive constraints of the train-set's dispatch, the connecting conditions, the principle of uniqueness for train-sets, and the first plus for connection in the same direction based on time tolerance σ. A compact connection algorithm based on time tolerance is then designed. The feasibility of the model and the algorithm is proved by the case study. The result indicates that the circulation model and algorithm about multiple routing can deal with the connections between the train-sets of multiple directions, and reduce the train's pulling in or leaving impact on the station's throat

Maintenance schedule optimisation for a railway power supply system

High reliability is the crucial requirement in railway operation and a power supply system is one of the key components of electrified railways. The cost-effectiveness of the maintenance works is also the concern of the railway operators while the time window on trackside maintenance is often limited. Maintenance scheduling is thus essential to uphold reliability and to reduce operation cost. It is however difficult to formulate the optimal schedule to meet both reliability and maintenance cost for a railway power supply system as a whole because of its functional complexity and demanding operation conditions. Maintenance scheduling models to achieve reliability and maintenance cost are proposed in this study. Optimisation algorithms are then developed to attain the solutions of the model. The applicability of the models and efficiency of the solution algorithms are demonstrated in an example. The proposed methods are vitally important for the railway engineers and operators to assure the service quality in the increasing demands of the modern electrified railways

The pigmental composition and the absorption spectral analysis of Ulothrix sp. and benthic diatoms in the intertidal zone of Great Wall Station, Antarctica

This paper reports the results of the absorption spectral analysis of Ulothrix sp. attached to the rocks from the intertidal zone in front of Great Wall Station, Antarctica in February 1989, and the benthic diatoms growing on small stones and on the edge of swamps of that zone. Six kinds of pigments were separated and identified in benthic diatoms. They are carotene, chlorophyll-a, fucoxanthin, chlorophyllin, neoxanthin and chlorophyll-c. Nine kinds of pigments were identified in Ulothrix sp. . They are carotinoid, pheophytin, chlorophyll-a, -b, chlorophyllin, chlorophyllide-a, neoxanthin, chlorophyll-c and pheophytin-c. The intertidal benthic diatoms and Ulothrix sp. have specific absorption spectra and there are also marked differences in the composition of algal pigments they contain. Since the pigments of marine algae show differences in their absorption spectra, the absorption spectrum can be used to identify the species of marine algae

Computation on Bus Delay at Stops in Beijing through Statistical Analysis

Delays at bus stops have seriously affected the efficiency of bus operation and the improvement of level of services of public transportation and greatly influenced the preferences of passengers to choose bus services. In this paper, the analysis on arriving, dwell and leaving process of buses and the method to calculate bus delays at stops are proposed according to survey data from three bus routes in Beijing. Statistical analysis is then adopted respectively to evaluate average times that buses are docking at curbside and bay-style stops. Moreover, it is noted that different load factors of passengers in buses have significantly influenced the average boarding and alighting time per person. The effectiveness and accuracy of the proposed methods is illustrated through case studies. This study is crucial and helpful for the planners and operators to evaluate the efficiency and level of service of urban public transportation