IN terms of high-speed rail (HSR) network length, no country comes close to China, whose system had reached 12,183km by October 2014. To put this in context, China has constructed almost four times as much high-speed railway as Spain, which has the world's second largest network. Today most of the metropolitan regions in China are either connected, or in the process of being connected, to lines with a maximum speed of 200km/h or above.

By July 2014, China Railways Corporation (CRC) was operating more than 1330 China Rail High Speed (CRH) services a day on both the high-speed network and upgraded conventional lines. More lines are being built and upgraded to connect all cities of more than 500,000 people with services of at least 160km/h by this year. Since China's first truly high-speed line only opened in 2008, this represents a radical change in the provision of passenger services by CRC in a very short time.

However, building new infrastructure or providing services is not an end in itself and when the high-speed programme was announced there was much debate over whether the projected traffic would materialise and whether the cost of constructing such a system could be justified.

Nearly seven years after the opening of the first high-speed line, insights into usage have begun to emerge and many important questions can now be answered. What is the traffic level and how does it compare with air traffic? Who is travelling on CRH services? Has high-speed rail benefited ordinary citizens? These answers are important for informing policy and regulations, as well as optimising train services.

By October 1 2014, CRH had carried more than 2.9 billion passengers since its launch. Traffic increased from 128 million in 2008 to 672 million in 2013 with annual growth of around 39% during this period.

In 2013, Chinese high-speed traffic reached 214 billion passenger-km, slightly more traffic than the rest of the world's high-speed networks combined and around 2.5 times the volume carried in Japan, which has the second-busiest network. These are substantial numbers for a system that is still in its early days.

China is unique in many of its characteristics, be it for its sheer land area (9.6 million km²), the long distances between north and south, east and west, its current stage of economic development (GDP of $US 6807 per capita in 2013) and its population density (141 people/km²), particularly in central and eastern provinces. It has many well-dispersed large cities of more than 500,000 inhabitants located 200-900km apart, ideal territory for high-speed rail.

China is also at a turning point in its urbanisation, a strategic time to put in place the transport backbone that will stimulate the overall competitiveness of cities. In 2013, 53% of the population was urbanised but by 2030 this will increase to 70% or around 1 billion people.

According to the 2010 census 221 cities have a population of more than 500,000 and 81 cities are home to more than a million inhabitants and more are expected to join their ranks as urbanisation continues. Those cities will seek to develop their service industries and play a major role in the growing domestic economy. Competitiveness will be influenced by the quality of their transport links to innovation networks and to supply chains, both national and international.

China is also seeking to rebalance economic growth geographically, and after 30 years of rapid development in the eastern provinces, development of central and western provinces has become a prime objective for the government, with improved connectivity expected to play a central role in this rebalancing. The completion of high-speed links to Xinjiang in the west and Guizhou in central China at the end of 2014 demonstrates this policy in action.

As these changes occur, international benchmarks show that the average distance travelled is likely to increase significantly as China's per capita GDP increases. If the average Chinese citizen were to travel as much as the average Japanese, European or American, the distance they travel would be multiplied by four, five or 10 respectively by 2030, compared with 2012 levels. As the Chinese economy grows in sophistication and the population becomes more affluent, service levels will also need to be raised.

While new transport demands are emerging and existing transport needs are growing, the CRC network is already one of the most densely used in the world, with robust growth between 2009 and 2013. Overall passenger traffic grew by 5.5% per year during this period reaching 2.1 billion passengers or 1060 billion passenger-km in 2013. Railfreight grew by 6% per year to 3.6 billion tonnes, or 2633 billion tonne-km in 2013. These are large volumes compared with the size of the network (103,100km in 2013).

China-HSThe combination of rapidly growing traffic and of high existing traffic density meant that major investment would be needed if rail continues to play a key role in the economy.

The government's Mid-to-Long Term Railway Network Plan adopted in 2004, and updated in 2008, laid out a development strategy for the network for the period up to 2020, including the connection of all provincial capitals and cities above 500,000 people to a rapid rail network of 45,000km, including about 16,000km of high-speed lines. The programme was later accelerated to achieve most of these objectives by 2015.

The CRH network was launched in April 2007 with a new generation of trains capable of operating at up to 250km/h, although initially most mileage was covered on upgraded conventional routes. The need to share track with freight trains meant average station-to-station speeds remained moderate, even if maximum speeds had improved substantially. With a 10-hour trip, the average speed between Beijing and Shanghai had reached 132km/h.

In 2008, the first of a new generation of high-speed lines began operating. The Beijing - Tianjin high-speed line opened in August 2008, with a maximum operating speed of 350km/h and an average station-to-station speed of 240km/h. It quickly established itself as a competitive form of transport, carrying over 16 million passengers in its first year of operation.

By December 2012, both the 1318km Beijing - Shanghai and the 2281km Beijing West - Guangzhou high-speed lines had been completed, connecting the three most vibrant economic clusters in China. By international standards these lines offer extremely competitive journey times, with the caveat that many stations are located outside central areas, and thus require additional connection time. For example the Beijing West - Zhengzhou East CRH service offers an average station-to-station speed of 289km/h with a journey time of 2h 24min for the 693km trip. The average speed for Beijing - Shanghai is 275km/h and the 1318km journey takes just 4h 48min.

On July 1 2014, CRC introduced a new summer timetable with 1330 CRH services per day. Aside from increasing CRH capacity, the new schedule enabled a shift towards more high-speed services and an increase in freight traffic on conventional lines, which was one of the original goals of developing the high-speed network.

Nevertheless, the new timetables raised some concerns. Service levels did not differentiate between peak and off-peak periods and few discounts were offered for services with lower demand. This may result in lower occupancy rates on off-peak trains, while tickets for peak trains will remain difficult to obtain. A number of conventional services were also replaced by CRH, reducing options for low or middle-income passengers who may be less time sensitive but more price sensitive. These concerns could be addressed in part by introducing additional flexibility in pricing with discounted tickets during off-peak periods.

All CRH trains are formed of eight or 16 cars with capacity ranging from 494 to 1299 seats. The busiest routes can be served by up to 101 services per direction per day, with up to eight trains per hour at peak times. Traffic density on such routes is estimated at about 30-40 million passengers. Two types of services are provided; express trains stopping only at major cities while other trains stop at intermediate stations. On medium density routes, 40-50 trains operate daily.

Fares vary depending on the speed of the services. Second class fares for 200 to 250km/h HSR services are about $US 0.045 per km, similar to intercity bus fares. Second class fares for 300 to 350km/h HSR services are $US 0.077 per km, lower than or comparable with discounted air fares. This is three to four times the fare for conventional express trains, but tickets for these services are often difficult to obtain and the level of service is significantly lower. The low-cost of high-speed fares compared with other countries reflects the substantial traffic densities and occupancy rates, and the lower cost base for construction and operation.

During 2008-2013, total rail passenger volume continued to grow at 7.6% annually, but with a change in traffic composition. While conventional rail traffic grew 1.5% annually, CRH traffic has increased 39% per annum since 2008. The introduction of CRH services has not caused a reduction in ridership on the conventional network, but has instead fuelled accelerated growth, which the previous network, close to its full capacity, was unable to achieve.

By October 1 2014, CRH had carried an estimated 2.9 billion passengers, an estimated 1.9 billion of whom travelled over the dedicated high-speed network for at least part of their journey.

In 2013, CRH services carried an estimated 672 million passengers equivalent to 32% of all rail journeys in China, and CRH passenger volume reached 221.7 billion passenger-km. The average distance travelled reached 330km and average distances are increasing steadily as the network expands. The large number of passengers on short-distance CRH services lowers the average.

The two busiest lines are Beijing - Shanghai and Beijing - Guangzhou, each estimated to carry more than 100 million passengers in 2014. Few of these passengers travelled end-to-end and the average trip length on both corridors is about 500km. The first long-distance line, the 969km Wuhan - Guangzhou line carried around 50 million passengers in 2013, about 14 million of whom came from interline traffic, illustrating network effects. Around half of the ridership on this route came from conventional services with the remaining traffic being new-to-rail. According to a report in the People's Railway Post in January 2014, the average seat occupancy on CRH services was 70% in 2013.

While HSR has experienced stronger growth than air transport, the two modes remain quite different in their features. In 2013, twice as many passengers travelled on CRH services (672 million) as domestic flights (327 million) and while domestic air traffic increased continuously at an average of 13% per year between 2008 and 2013, CRH growth has been substantially faster, averaging 39% per year. However, the average air trip was substantially longer at 1363km in 2012 and is getting longer, presumably as flights covering distances of less than 800km tend to be withdrawn when faced with high-speed rail competition.

For short trips (less than 150km), car and bus often remain competitive, especially if the high-speed station is located far from the city centre, while for journeys of more than 1000km air is still an attractive option. Nevertheless, the reliability, frequency and comfort of CRH services make rail competitive for most middle-distance trips and in some cities, such as Baoding, CRH has even become a commuting option.

While the high-speed network in China will quickly reach maturity, traffic is still in its early days as the experience of Japan and France, the two leaders in high-speed traffic outside China, has shown. Judging from both of these examples, and from the forecast increase in mobility in China, the current level of traffic is relatively strong. In 2013 after five years of CRH operations, high-speed passenger density (defined as passenger-km divided by the average length of high-speed lines in operation) had reached 22.5 million, close to the level reached in France (25 million) after 32 years of operation. While it will take longer to reach the current level in Japan (36 million), China's current level of traffic compares favourably with Japan at the same stage of development.

Considering the overall development context in China, rapid traffic growth looks set to continue over the next two decades, with levels closely related to the pace of economic development. This network also offers high transport capacity, a feature particularly relevant during the peak traffic periods. Experience in France indicates traffic could be further expanded by offering differentiated pricing strategies based on occupancy rates.

The level of demand seen so far confirms a strong need for such a service along core corridors, and passengers' willingness to pay higher fares.

In May 2013 CRC, the World Bank and China's Third Railway Survey and Design Institute surveyed 1001 passengers on conventional and high-speed trains on the Tianjin - Jinan and Jilin - Changchun routes. This showed that a large proportion of high-speed passengers - 62% based on the Tianjin - Jinan route - belong to the 25-55 age group. Many of these passengers were travelling for business, with high-speed rail facilitating an increase in trip frequency for businesses.

The research found that a broad range of travellers from different income levels choose CRH for its comfort, safety and punctuality over existing alternatives. Users perceive it as facilitating reunions with family and friends, tourism, and access to job opportunities.

The self-reported income levels from the on-train survey suggests that the majority of passengers had monthly income of less than Yuan 5000 ($US 805) per month (50-70% of users in the two case studies). The high-speed passengers' average income was 35-50% higher than that of passengers on conventional trains. High-speed appears to have filled a gap in the type of services previously offered.

As the network develops, there will be a clear need to pay careful attention to the overall door-to-door trip experience for travellers. This includes dealing with aspects that sometimes extend beyond the remit of the railway, for example by improving station access, and, in particular, reducing the waiting times for taxis or ensuring high frequency local public transport services. It also includes optimising train frequencies and stops based on emerging trip patterns and user surveys, introducing flexible ticket prices reflecting peak/off-peak periods, and introducing convenient e-ticketing.

By focusing on these aspects, and on the efficient operation of the network, high-speed rail in China can be expected to continue to experience substantial growth for years to come.