بهینه سازی سرعت مورد نظر در قطارهای راه آهن با سرعت بالا برای صرفه جویی در انرژی کششی و بهبود بهره وری حمل و نقل

In the pursuit of higher operation speed at the passenger train services in China, the impacts of high-speed operation on energy consumption and transport efficiency are however not clearly identified. This research attempts to analyze the traction energy cost and transport operation time per 10,000 passenger-kilometers of high-speed railway (HSR) trains with a range of target speeds on certain HSR lines in China through a simulation approach. Having considered the effect of inter-stop transport distances, traction characteristics of HSR trains and gradients, curvatures, etc. of the rail lines, this study has deduced that the target speed of a HSR train for an inter-stop transport distance shorter than 100 km should be below 190 km/h from the perspectives of traction energy saving and transport efficiency improvement. Moreover, the study results also indicate that, unlike the actual HSR operation, the target speed should be dynamically adjusted according to the transport distances between stops if the transport capacity of the rail line is not extensively used. The exact target speed for each inter-stop transport distance shorter than 100 km should be further determined according to the traction characteristics of the train and the track geometry of the rail line.

High-speed railway (HSR) development in China has been travelling on a fast lane in recent years. It started with the China Railway High-speed (CRH) Electrical Multiple Unit (EMU) type-3 (CRH3) providing passenger transport services with the maximum speed of 350 km/h between Beijing and Tianjin from August 2008 (Yang et al., 2010). As of July 2011, there are various types of CRH EMUs running with the maximum speeds over 200 km/h on more than 8000 km HSR lines in China. According to the plan of the Ministry of Railways of the People's Republic of China, over 23,000 km HSR Lines will be constructed and put into services by 2015. Despite numerous on-going studies on the CRH EMUs' shapes, structures, cardan shafts, etc. (Zhang et al., 2006, Yao et al., 2009, Huang et al., 2010 and Sun et al., 2010), the maximum speeds of the CRH EMUs have been raised continually, together with the accelerated construction of the HSR lines in China. In late 2010, the maximum speed of 486 km/h was attained by the CRH EMU type-380A on the newly constructed HSR line between Beijing and Shanghai. The extraordinary progress of the high-speed train services and the rapid construction of HSR network in China do not go without inevitable questions from railway researchers and engineers. When the maximum speed is raised, higher traction effort is required (Hay, 1982, Andrews, 1986, Martin, 1999 and Mao et al., 2008), which implies different patterns of energy consumption (Kokotovic and Singh, 1972, Uher et al., 1984, Hoyt and Levary, 1990, Liu and Golovitcher, 2003, Chandra and Aqarwal, 2008 and Huang and Qian, 2010). It is then necessary to investigate how the traction energy cost of a HSR train changes under a range of target speeds, taking into account the effect of inter-stop transport distances, traction characteristics of HSR trains and gradients, curvatures, etc. of the rail lines. Because of the demand on shorter travelling time, HSR system swiftly expands its market within China and beyond (Adler et al., 2010 and Hsu et al., 2010) and it is competing with other transportations on long-distance commuting (Hatoko and Nakagawa, 2007 and Blanco et al., 2011). However, investment cost recovery and marketing strategies are hardly addressed (Hensher, 1997, Cheng, 2010 and Chou et al., 2011). In particular, time-saving (i.e. in other words, improvement of transport efficiency) may be achieved by various target speeds and the cost to attain such an improvement through high-speed operation should be evaluated. Furthermore, when the target speed of a HSR train is connected to both energy saving and transport efficiency, the setting of its target speed to improve both of them is essential to the service quality and operation cost. Many previous studies attempt to interpret the relationships between speeds and traction energy consumptions (e.g. Chui et al., 1993, Lukaszewicz, 2001, Miller et al., 2006, Bocharnikov et al., 2007 and López et al., 2009) as well as transport efficiencies (i.e. transport efficiencies) of various kinds of trains (e.g. Wong et al., 2002, Liu et al., 2007 and Hsu et al., 2010). However, these studies usually focus on the changes of total energy cost and gross time loss of a train with the increase of the number of its stops along a rail line. They are not able to provide quantitative evaluations of both energy and time saving with respect to target speeds of trains under different inter-stop transport distances, traction equipment characteristics and rail lines' gradients, curvatures, etc. By analyzing the effect of these factors on the Traction Energy Cost (TEC) (i.e. energy consumed due to motoring, coasting and braking) and Technical Operation Time (TOT) (i.e. travel time excluding the time expended by stops in stations) per 10,000 passenger-kilometers (p-km), this work propose to optimize the target speeds of HSR trains in a quantificational manner from the perspectives of both traction energy saving and transport efficiency improvement. This research is based on the simulations of the passenger transport services by the HSR-Train-Type1 from Stop-A to Stop-B of one certain HSR line and the HSR-Train-Type2 from Stop-C to Stop-D of another HSR line in China. This paper is organized as follows. The simulation approach to calculate the TEC and the TOT of a HSR train is first explained in Section 2. Thereafter, Sections 3 and 4 analyze the TEC per 10,000 p-km and the TOT per 10,000 p-km of various types of HSR trains with different target speeds between different stops, respectively. Based on the results attained, the performance of introducing the variable Technical Operation Cost (TOC) per 10,000 p-km is evaluated in Section 5. Finally, conclusions are given and future research issues are discussed in Section 6.

For a given utilization ratio of the passenger seats, it is revealed that the increase of the TEC per 10,000 p-km of a HSR train is much faster than the increase of its target speed. Moreover, if the target speed is higher than 180 km/h, both TEC and TOT per 10,000 p-km increase significantly with the decrease of the inter-stop transport distance below 100 km. Different traction characteristics of HSR trains may make the same inter-stop transport distance have dissimilar effect on the TEC and TOT per 10,000 p-km. Furthermore, when the inter-stop transport distance is shorter than 50 km, changes of the TEC and TOT per 10,000 p-km with the increase of the target speed will be stopped by preventing the train from accelerating to exceed a maximum speed over 300 km/h in such a short distance. In addition, track geometry of the rail line generally adds the resistance against train traction, which generally increases the TEC per 10,000 p-km. However, the coasting time of a HSR train may happen to be extended because of the upper speed limits required by the gradients, curvatures, etc. of the rail line, and therefore the TEC per 10,000 p-km of the train may be decreased. It is empirically confirmed that, in view of traction energy saving and transport efficiency improvement, the target speed of a HSR train with a certain utilization ratio of its passenger seats should be lower than 190 km/h if the transport distance between stops is shorter than 100 km. The target speed of a HSR train ought to be dynamically adjusted according to the inter-stop transport distances especially shorter than 100 km if the transport capacity of the rail line has not been extensively utilized, rather than being kept consistent for the whole trip from the station of origin to the station of destination in the actual HSR operation. The exact target speed of the train for each stop-spacing should be further determined based on the necessity of the rapid transport service, the traction characteristics of the train and the track geometry of the rail line. Moreover, different fares should be determined mainly according to the target speeds of the HSR trains. However, this principle has not been fully considered in the HSR transport work in China. In this work, only the performances of two types of Chinese HSR trains are analyzed for their passenger transport services on certain HSR lines in China. The transport operations of more types of HSR trains should be comparatively studied for other HSR lines to further validate the conclusions in this research. Moreover, determination of the target speed of a HSR train in consideration of more factors, e.g. utilization ratio of the passenger seats, aerodynamic impacts, etc., from a more comprehensive perspective also needs to be further explored in the future work.