The Implication of URT in China
Public transit is more than a means of transportation. It plays a critical role in facilitating the city’s competitiveness. High-quality transport services and infrastructure improve the labor market performance, attract inward investments and help to create an improved quality of life. Below are examples of some research based on Minneapolis–St. Paul (MSP) area. Tilahun and Fan  found out that the growth of jobs along transitway corridors would achieve the best regional transit accessibility gains. From Fan, Guthrie and Levinson’s  study, light rail stations and bus stops offering direct rail connections are associated with large, statistically significant gains in accessibility to low-wage jobs. Owen and Levinson  had demonstrated the feasibility of accessibility-based mode share modeling and predicted the likelihood that a commuter will choose transit rather than auto for a commute trip based on aggregate characteristics of the surrounding area. Fan and Guthrie  did an individual dimensions survey along four transit corridors in this area to explore the broader neighborhood impacts of transit investments as perceived by neighborhood residents. They found out some significant differences existed between urban and suburban areas and between individual neighborhoods. Tong et al.  constructed a time-dependent space–time network where the traveling arcs and activity performing arcs were introduced to analyze the accessibility of Chicago. Foth et al.  developed a methodology using a social indicator based on census tract level socioeconomic characteristics to measure the relationship between social disadvantage and accessibility to jobs and transit travel time in the Toronto region over time.
Meanwhile, more than improving the accessibility of the residents, the urban rail transit systems also have positive economic impacts on the cities. Knowles and Ferbrache  did a study on light rail systems, and they found out that the light rail systems improve the economic growth by increasing the attraction of locations for inward investment.
Urban rail in China has attracted fairly high ridership. Taking Beijing as an example, in 2015, the average passenger every day is 9.36 million and 25% of the commuters take the metro system to go to work, which is the same as the bus system. Every city tries to improve the coverage of the urban rail transit and provide higher accessibility to the residents. Table 4 gives out the line density and the service length sharing by residents in top 10 operational systems in China. In Chongqing, the urban rail transit system covers most of the area in the city and its line density has reached 0.728 km/km2. Dalian and Nanjing ranked the second and the third, respectively, having reached 0.526 and 0.462 km/km2. In terms of the service length per resident, Nanjing ranked in the first place and reached 0.0283 m/person, followed by Shanghai and Beijing.
Moreover, the government invested in the urban rail system steadily every year, and in 2015, the investment has reached to 368.3 billion RMB (approximately equivalent to 56.7 billion US dollars), and for the next 5 years. The urban rail transit will play a more and more significant role in public transportation. The trends of urban rail transit in China are discussed below.
Trends of Urban Rail Transit in China in the Next Five Years
A Decade of Rapid and Large-Scale Development
The urban rail transit system experienced a rapid development in China during the last 10 years. In the past 5 years, 1867.5 km of new lines was opened. In the next 5 years, the urban rail transit in China will continue to grow. Figure 5 shows the distribution of the cities with urban rail transit. The dashed line is the Heihe-Tengchong Line or population density line. On the east, it covers 95% of the population in China, 43% of China’s area, and lies in regions where the economy is more developed. All of the cities with urban rail transit service are under the dashed line. Most of the cities are distributed in the big cities of the province and the coastline area of China, especially in the Yangtze River Delta region (the blue dashed ellipse in Fig. 6) and Pearl River Delta region (the pink dashed ellipse in Fig. 6) . However, some cities in the west part of China have started to construct urban rail transit systems, such as Urumchi and Lanzhou. Because of the limited road density, for instance, in 2004, Beijing road network was 14,557 km with 1 m/capita length of road Ahmed et al. ; in order to mitigate the traffic problem, the urban rail transit systems are constructed. There were in total 3821 km, 147 urban rail transit lines under construction in 38 cities by the end of 2015. By the end of 2020, over 3000 km new lines will be opened and the total service length will reach up to 6000 km. The proportion of urban rail transit in public transportation will increase.
During the past 5 years, the investment for urban rail transit in China is 1228.9 billion RMB (approximately equivalent to 189.1 billion US dollars) in total, as shown in Fig. 7. The average investment is 245.8 billion RMB (approximately equivalent to 37.8 billion US dollars), with a steady growth of 51.4 billion every year. In the next 5 years, the total investment will reach up to 1700–2000 billion RMB and some new investment mode such as PPP (Public–private partnership) will be adopted [28–30].
Meanwhile, there were 55 cities planning to build urban rail transit systems by the end of 2015. Table 5 shows the urban rail transit planning in every city with operation lines. Almost every city plans to construct urban rail transit systems with a length of more than 500 km. The total planning length will reach 15,000 km in China. The construction work for the next 5 years is a big challenge.
Attraction of More Passengers
In the past 5 years, there were totally 52.8 million passengers choosing urban rail transit. The annual ridership from 2011 to 2015 is shown in Fig. 8. Passenger travel behaviors changed a lot during these 5 years. With the development of urban rail transit and the network operation, the passenger volume is expected beyond 16 million in 2016. The total passenger volume for the next 5 years will be over 100 million.
Network Organization Patterns
By the end of 2015, there were 10 cities whose service length will reach more than 100 km and 18 cities building more than two lines. There were 384 transfer stations, which accounted for 17.2% of all stations in service. Meanwhile, there are 2075 stations under construction, in which the transfer stations reached 609 and occupied 29.3% of the total stations. The increasing proportion of the transfer station indicates that the urban rail transit lines have evolved into a network where different lines intersect and correlate with each other, instead of a single line. At the same time, the ridership is increasing during these 5 years. In Beijing, the daily ridership increased from 5.97 million in 2011 to 9.36 million in 2015 , an increase of 56.8%. For some transfer stations, such as Xizhimen Station, the daily ridership is over 1 billion. In order to integrate resources and the passenger flow, many cities with urban rail transit in China are exploring transport organization patterns under network operation, such as flexible marshaling and express and local trains [32–34].
Flexible marshaling According to the passenger characteristics, the trains can be marshaled flexibly which could not only save transport capacity but also improve service levels. In April 2010, Guangzhou Metro Line 3 first adopted flexible marshaling technology, with a unit of three cars. During peak hours, the train is marshaled with two units and one unit during off-peak hours to adapt to the tide phenomenon of the passenger flow. Similar to Guangzhou Metro Line 3, Shanghai Metro Line 16 uses the same marshaling mode [35, 36].
Long–short loop Besides Beijing Metro Line 6, as shown in Fig. 4, Beijing Metro Line 4 and Shanghai Metro Line 2 are also using the long–short loop organization pattern.
Express–local train The essence of express and local train operation is to decide the stopping of express trains and local trains based on the section passenger volume, with the express train stopping at fewer stations and traveling less time. This pattern has an advantage in reasonably distributing transport capacity, cutting down traveling time of long-distance passengers and improving transportation efficiency of the system. In China, such as Beijing Metro Line 6, express trains and local trains run on separate tracks, while in Shanghai Metro Line 16, the express trains and local trains will run on the same track with four overtaking stations [37–39].
Feeder bus To guarantee the passenger demand, it is inevitable for urban rail transit to cooperate with other public transportation. With the coordination of the Traffic Committee of Guangzhou, Guangzhou Metro has enhanced the cooperation with Guangzhou Bus Company establishing a long-term cooperation. Once emergent events occur, free feeder buses will be provided to ease the transportation pressure of urban rail transit greatly and bring convenience for passengers [40–43].
Besides these operation strategies, some of the cities consider the network comprehensively and connect the lines together. Chongqing is working on the interconnection project and has tried to improve the flexibility of operation for different lines. Meanwhile, there is an urban rail transit planning for the Yangtze River Delta region and Pearl River Delta region in the next 5 years, and some new operation strategies will be developed to cater to the needs of the passengers.
Multi-type Urban Rail Transit
China is such a vast area, and the land use and landscape vary. Every city has its own characteristics. For example, Chongqing is located in the southwest of China and is mainly covered by hills and mountains. The unique landscape promoted the development of monorails, which have the outstanding capability of climbing steep slopes . Meanwhile, the investment of tram construction is much less than that of the metro, and the capacity of the tram can meet the demand of the public transportation in some small cities, such as Changchun, Shenyang and Dalian, as shown in Fig. 9. Meanwhile, in the past 5 years, other types of public transportation such as APM (automated people mover systems) and light rail transit developed. Figure 9 indicates the urban rail transit type in every operational system.
In 2015, the proportion of metro system has decreased to 67% in terms of the urban rail transit projects under construction. In the next 5 years, the city scale will increase and stretch to suburb areas and some satellite cities. In order to connect with the downtown and satellite cities, considering the passenger flow and construction cost, more and more cities will choose the tram and light rail instead of the metro system. Some cities surrounding by hills will select the monorail to handle the huge passenger demand [45, 46].
With the rapid development of urban rail transit in China, we also can share the experience with other developing mega cities such as Karachi, Hanoi, Mumbai and Delhi. In the next 5 years, in order to develop the urban rail transit sustainably, we should integrate the land use and transportation, improve the traffic management and promote public transport and development based on transit-oriented development .