Addressing the occupancy problem of Soekarno-Hatta Airport rail link during its first five years of operation

Airport rail links have long been acknowledged as a crucial component of the modern transportation system. Their attractiveness among air travellers stems from their convenience, speed, and environmental benefits. Despite their advantages, these services often face several occupancy problems that hinder their effectiveness and efficiency. Soekarno-Hatta airport rail link’s operation in 2018-2022 has been marked by low occupancy. This study aims to assess the realisations of several critical attributes of a successful airport rail link service according to TRB studies in the context of the Soekarno-Hatta airport rail link. In this context, it was shown that only four of the seven key attributes have met the minimal level to attain such goals. Despite numerous strategies undertaken during the period, which coincides with the COVID-19 pandemic, most fall under the operating or service adjustments category. The minimal realisations of the seven key attributes confirm the low occupancy levels, yet efforts to increase the ridership were limited during the pandemic. These findings provide avenues for a more successful transfer of operations from PT Railink to PT Kereta Commuter Indonesia with the clear intention of boosting the rail link’s ridership. Alongside several expansion plans by the Directorate General of Railways, the findings shall help public policymakers promote a modal shift and pave the way towards a broader integration with other modes of public transportation in the Jabodetabek region.


Introduction
Since its launch in early 2018, the Soekarno-Hatta Airport rail link (SHARL) has enabled high connectivity between the airport and the surrounding area of Banten and Jakarta provinces.Being only Indonesia's second airport rail link, the SHARL was intended as an alternative ground access mode to relieve road congestion to Soekarno-Hatta International Airport (SHIA).The SHIA is the primary airport serving the Greater Jakarta Metropolitan Area, also known as Jabodetabek (Jakarta, Bogor, Depok, Tangerang, Bekasi).The airport ranks among the world's busiest airports: in 2018, SHIA was used by more than 66.9 million passengers, making it the 18th busiest airport in the world [1].The 37.3-km journey between the Airport station (Bandara Soekarno-Hatta station) and Manggarai station takes about 56 minutes, stopping at three stations in between, namely the Batu Ceper, Duri, and Sudirman Baru (BNI City) stations.From the four stations outside SHIA, passengers may transfer to Jabodetabek

Literature review
Several studies have explained that ground access to airports is an essential aspect of urban public transportation planning, most notably to serve a high number of trips generated by airline passengers and airport workers [8,9].Research by TCRP in the United States, as quoted by Mandle et al. [8], mentioned eleven types of airport ground access modes with railway, scheduled (express and multistop) buses, and shared-ride or door-to-door vans categorised as public transportation modes.In contrast, private vehicles, rental cars, courtesy vehicles, airline crew vehicles, taxicabs, town cars, prearranged limousines, and chartered buses and vans are categorised as private transportation modes.Public transportation modes are defined as the services available to the general public and aim to transport multiple passengers travelling at one time [8].
Furthermore, Schabas [9] grouped airport rail link services into five broad categories, namely: 1. a metro or rapid transit line to the CBD; 2. a dedicated express railway to the CBD; 3. a major station within the regional rail network; 4. a station on a commuter rail line/network; and 5. a hybrid commuter and express rail line to the CBD.Schabas' study also differentiated the characteristics of two primary user groups of airport rail link (or airport access modes in general): the airline passengers and airport workers, listed in Table 1.The airline passengers' market was further categorised based on their trip purposes and residential status [5], as illustrated in Figure 1.
A study by de Neufville [10], which explained the effect of LCCs on the planning of airport ground access transportation, reveals that the operating model of LCCs is aimed at serving demands from smallsized feeder airports within a metropolitan area.The LCCs' model differs from full-service legacy carriers as they mainly operate from larger main airports, the so-called "fortress hubs" in the US.Thus, airlines operating out of smaller airports can reduce their airport-related expenses and, in turn, minimise IOP Publishing doi:10.1088/1755-1315/1294/1/0120223 the tariff imposed on their passengers.An airport primarily serving a price-sensitive market (i.e., preferring cheaper air tickets) means the viability of building an expensive, dedicated airport express railway towards such an airport is low, considering it will not attract high levels of ridership.In all, de Neufville suggests building an affordable airport access mode in parallel to facilitating door-to-door travel throughout the urban area by integrating it with existing transit modes and opting for more costeffective alternatives [10].
Table 1.Characteristics of air passengers and airport workers using airport rail link.(Source: [9])

Air Passengers
Airport Workers/Employees • Air passengers who are also residents have a relatively dispersed residential origin/destination within the region (hence the need for more connections), while nonresidents primarily head for the CBD.
• Airport employees may form a captive market because they carry no luggage, travel to their workplaces at fixed times, and are more pricesensitive than air passengers.
• The type of air traveller (business or leisure) may indicate his or her willingness to pay and desired quality of service besides the origin/destination location at the city-end of the trip.
• The employees' usage of airport rail links might be low since their workplaces are not concentrated in one place, and their working shifts usually extend beyond public transport running hours.
• The type of airline operating from the airport (low-cost carriers/LCCs or fullservice airlines) determines a passenger's willingness to pay for more premium rail services and the potential of using public transport at all if travelling in groups.
• As they are more price sensitive, employees of the airport and surrounding areas might be attracted to using commuter rail line that extends to the airport as a viable alternative to premium rail services.
Figure 1.The "Four Cell Matrix" of the four market segments of air passengers using the airport rail link.(Source: [5]) In the context of the differing passengers' and workers' demands, it is noteworthy to distinguish dedicated and shared public transportation services to airports, as defined in [5].When airport link services and vehicles are designed specifically to meet the needs of air travellers, they are categorised as dedicated services.On the other hand, air travellers using shared services are provided with the same vehicle types run in the same corridor as other public transportation passengers.Moreover, while most dedicated services offer direct, high-speed service to only one terminal in the downtown area, most shared services call at several stations upon entering the urban or downtown area, thus making for a relatively slower service but many intermodal transferring points [5].As for key factors of successful rail-based airport access modes, our study refers to the seven desired attributes summarised in [5], which are explained in Table 2.At most airports, less than 15% of all travellers end their trips in the downtown area.Hence, the coverage area of a direct airport rail link to the downtown or CBD only serves a relatively small percentage of the total air passenger market.

Characteristics of the air traveller market
While air travellers with little or no checked baggage tend to use rail link service, large family groups (often including well-wishers) refrain from using rail.The passengers' familiarity with local public transit systems also creates a potentially high rail link ridership.

Regional travel time
The availability of a direct service to avoid the need for transfers or multiple stops is essential.Among the concerns of air travellers that drive them towards using rail service are: i) uncertain travel times on airport access roads and ii) the lack of or the difficulty of finding a convenient parking space at the airport.

Ability to walk between station and destination
Rail service is more attractive to air passengers if it is within walking distance from their final destination at the airport, hence completing door-to-door travel.The need to transfer to a second mode once they arrive at the station may shift travellers away from using the airport rail link.

Extent of regional coverage
A large catchment area means more accessibility for passengers, resulting from the interconnectivity between the airport rail link and the wider railway network, thus serving a more significant portion of the market.

On-airport travel time
Similar to factor no. 4, a more convenient airport rail service may yield when air passengers are only required to travel between the station and the aeroplane gate within a short time and distance.Another supporting factor is the airport's terminal layout (single terminal vs. multiple terminal buildings).

Frequency of service
Waiting times of 10 minutes or less are preferred, and they need to be adjusted with the headway of the rail service.The availability of late-night and weekend services is also essential for passengers (and workers) who need to access the airport during early or late hours.
Another TRB study lists several strategies, actions, or initiatives that transport operators may seek to improve the ridership of public transit systems.Table 3 below summarises the four categories of such strategies; further details on the actions/initiatives can be referred to [11].

Marketing and information initiatives
• Marketing/promotional initiatives

• Information improvements
Fare collection/structure initiatives • Fare collection improvements • Fare structure changes

Methodology
We use a qualitative approach owing to the availability of data at the time of writing, which is mainly a secondary one.We then apply nonreactive techniques (see [12]), which are content analysis and existing statistics research, to extract information from the available data.The information will be discussed and compared with the theoretical definitions, guidelines and existing precedents.
As for the data concerned, some important datasets have been obtained, such as the ridership data of SHARL for the years 2018-2023 (monthly) from the Directorate General of Railways (DGR), Ministry of Transportation, and for January-April 2023 (daily) from PT KCI; as well as the annual ridership data of Damri Soekarno-Hatta airport feeder buses for the years 2017-2023 (aggregated data coverage for year 2023 is only for January-May) the from the Perum Damri.To obtain the most recent data related to SHARL's operations, we held a public seminar session on July 4, 2023, to which several stakeholders were invited, including the DGR and PT Railink.Other data sources will also be used, mainly the annual Air Traffic Report published by the Port Authority of New York and New Jersey (PANYNJ), which provides extensive statistical reporting of world's busiest airports; the annual Air Transportation Statistics published by the Statistics Indonesia (Badan Pusat Statistik, BPS); and the JABODETABEK Urban Transportation Policy Integration Project Phase 2 or JUTPI 2 report published by the Japan International Cooperation Agency (JICA).

An overview of transportation conditions 4.1. The Soekarno-Hatta Airport and its rail link
Soekarno-Hatta International Airport (IATA code: CGK, ICAO code: WIII), located in Tangerang Municipality, Banten, is one of two airports serving Jabodetabek region; the other airport is Halim Perdanakusuma Airport located within the province of Jakarta Special Capital Region (DKI Jakarta).In 2010-2022, the number of passengers travelling through SHIA is shown in Figure 2 [1, 13,14].The number of airlines operating are 30 international and 10 Indonesian airlines, of which eight national airlines operate from SHIA as their main hub [15].Based on BPS's data from 2010-2021, around 94-98% of the passengers are travellers originating or terminating at SHIA, indicating the potentially heavy land-based traffic coming into and from the airport [14].As shown in Figure 3 [4], the 37.3-km Soekarno-Hatta Airport rail link connects five stations: Bandara Soekarno-Hatta (BST), Batu Ceper (BPR), Duri (DU), Sudirman Baru or BNI City (SDB), and Manggarai (MRI).The first two stations are in Tangerang Municipality, and the remaining three are in DKI Jakarta.The journey takes about 52 minutes with a 30-minute headway, and the service operates between 05:00-22:37 daily [4].The ticket for an "executive" class ride costs Rp10,000-Rp50,000, whereas the "premium" class-trialled in mid-2021 and launched in early 2022-costs between Rp10,000-Rp30,000.For 15 months in 2018-2019, the service was also extended to Bekasi station before passenger facilities at Manggarai were completed.
The SHARL's ridership since launched in early January 2018 has fluctuated, as indicated in Figure 4 [4]; it peaked at 179,134 monthly passengers in November 2019.Another important metric is the load factor levels.Data obtained from the DGR, Ministry of Transportation had calculated a 28-day average of SHARL load factor: 42% on weekdays and 45% on weekends, with an average of 113 passengers/day on weekdays and 95 passengers/day on weekends [4].

Other modes of transportation
Some other public transport options for travelling to SHIA offer connections to the Jabodetabek region and beyond, such as Jabodetabek Airport Connexion (JA Connexion) large buses, other Jabodetabek and intercity large buses, and intercity shuttle vans (locally known as "travel") mainly travelling between Bandung (West Java)-SHIA routes [16].An overview of modal share to SHIA is obtained from the 2019 JUTPI 2 report (see Figure 5) [17], whose surveys were done in the year prior.Since the JUTPI 2 survey did not yet include SHARL among alternative modes going into and from SHIA, the public transportation modes were only represented by the large, medium, and small buses.
The Damri Soekarno-Hatta airport buses are one of the most popular alternative modes.The company operates large-bus services under the JA Connexion name and independently under its name from within and outside Jabodetabek.A Damri airport bus ticket costs Rp80,000-Rp130,000 (Jabodetabek) and Rp140,000-Rp200,000 (outside Jabodetabek).Figure 6 shows the region-aggregated share of Damri bus ridership in 2018 (referring to JUTPI 2 data obtained in that same year), totalling 7,118,811 passengers across the six regions [18].

SHARL problems, as identified in 2019 reports
In early 2019, two articles emerged detailing the problems of SHARL after just one year of operation.The reports agreed that SHARL's low occupancy must be addressed from both the city-end and airportend sides [6,7].The following points are the summary of the two reports.
• Assuming a projected "70% occupancy per trip", the modal split of SHARL was still low among all trips to or from SHIA, which numbered "around 5-6% of the estimated 16%" (as quoted).
The daily passenger numbers in November 2018 never exceeded 5,000.In addition, SHARL's capacity (in pphpd, passengers per hour per direction) is relatively low compared to similar services in other countries.

43,9%
29,8% • SHARL fares from Jakarta city centre were more expensive than other public transport modes, such as Damri shuttle buses (Rp75,000 for SHARL compared to Rp40,000 for Damri buses when the reports were published).• The Airport train station (BST) is not directly connected to any of the terminals at SHIA.
Passengers travelling to terminals 1, 2, or 3 must take the automated people mover system ("Skytrain") or the airport shuttle buses.Furthermore, the Skytrain stops at each terminal are not located on the same level as the departure or arrival levels or within the terminal building.Thus, interconnectivity at the airport side is poor.• Passenger access or transfer to SHARL stations in the city centre (SDB and MRI) was poor.When the reports were published, various passenger facilities were still in construction: the Jakarta MRT, which was due to have one station in the Dukuh Atas-Sudirman Baru area, the connecting corridor between SHARL's SDB and Commuter Line's Sudirman stations, and SHARL facilities at MRI.Moreover, SHARL does not serve Gambir or Jatinegara station, which enables better connectivity with intercity/long-distance train passengers who may opt to continue their journey by plane.On the other hand, there is a Damri bus service from Gambir to SHIA.• An "odd-even" traffic management policy on Sudirman and MH Thamrin streets during morning and evening rush hours has forced passengers using private cars to make a long detour to access SDB station.• There was (or is) a lack of coherent and coordinated policy among transport stakeholders to support the modal shift to SHARL.For example, expanding parking spaces at SHIA will encourage airline passengers to use private cars.
In conclusion, SHARL occupancy problems arose from competition with other modes (Damri buses), poor interconnectivity with other modes, station capacity constraints, and lack of coordination among the stakeholders, which posed challenges to its successful operation early on.

Airport rail link precedents in Asia
Some precedents of successful and unsuccessful airport rail links across Asia are presented in Table A1 (see Appendix).Among those services, the dedicated Express Line of Bangkok's Airport Rail Link is an example of an unsuccessful one.It was closed after just three years of operation, yet its counterpart, the commuter-type City Line, still operates today.

The realisations of the desired key attributes in the SHARL service 5.3.1. The proportion of air travellers with trips ending in downtown areas.
More detailed data is needed to make a conclusive statement of the share of air passengers' trips ending in Jakarta's CBD due to the ridership data being aggregated from all five stations.However, since the SHARL was first conceived in the 1980s, the planners had already considered two alternative routes, each with several stops beyond or near the borders of Jakarta's urban area, to mitigate such a possibility of low passenger share should a direct service be operated [19].Currently, the operational route follows the "most economical" alignment to build, although it deviated from the alignment mandated by the 2013 regulation [20], which links SHIA and Halim airport through a northerly route instead of a westerly one.The lessons from Bangkok's City Line and Express Line, and other surviving airport rail link operating with a commuter service, might also become noteworthy evidence to the statement.

The characteristics of the air traveller market.
From the JUTPI 2 survey results, about 22.0% and 12.0% of the SHIA air passengers stated "family matters" and "shopping/leisure/tourism" as their travel purposes, respectively [17].This information alone may indicate a high proportion of air passengers who travel in groups or carry heavier/more luggage.On the other hand, the highest share of trip purposes flying through SHIA comprised work-related travels, numbered 48.3% [17].Nonetheless, a relatively high modal share of combined car-based modes (taxis, online taxis, and cars) to SHIA accounts for about 73.7% of all trips (see Figure 5).In all, there is an opportunity for SHARL to serve the remaining market of individual passengers currently travelling by private and non-public vehicles.9 5.3.3.Regional travel time.Although it does not provide a direct service between SHIA and Jakarta's CBD, the SHARL completes its 37.3 km journey within one hour (52 minutes).Compared with other available road-based access modes (cars, vans, and medium to large buses), SHARL shall maintain a reliable travel time even during peak hours.However, a benchmark of a similar service, that is, Hong Kong's MTR Airport Express, would not justify the travel time that SHARL currently attains from a comparable total distance and number of stops (SHARL: 37.3 km distance, 52 minutes, five stations; MTR: 35.3 km distance, 28 minutes, five stations).Indeed, faster train service is needed for SHARL to gain significant advantages over the road-based modes.

The ability to walk between the final station and destination, and on-airport travel time.
One particular problem noted in the 2019 reports was the distance between the Airport station and the terminals.Passengers arriving by train must board the Skytrain or shuttle buses from the "Integrated Building" to finally get to their intended terminals.A 2019 study reflects the problem of the time between SHARL and Skytrain arrivals, specifically for flights arriving after 23:00, whose passengers cannot continue their journey by SHARL, although the Skytrain is still operating by that time [21].In-airport connection difficulties are exacerbated because none of the Skytrain stops are located within any of the three terminal buildings.Terminal 3, the largest terminal, is the farthest terminal from the Integrated Building, despite having a Skytrain stop relatively closer to its doorsteps than the other two terminals.

5.3.5.
The extent of regional coverage.Stopping at major transit stations-Duri, Manggarai, Sudirman Baru/BNI City-nominally shows that the SHARL's regional coverage is extensive when all the connected rail-based modes are considered, notwithstanding the other public transit modes (for example, TransJakarta BRTs).The Bekasi extension during 2018-2019 should have attracted more passengers; its closure was likely due to incomplete station and track facilities.Hence, the SHARL competed with more frequent commuter trains on the same corridor.However, such interconnectivity with other highspeed, high-capacity transport modes in the Jabodetabek region has yet to materialise in a significant increase in SHARL's ridership levels compared to Damri buses (see Figure 6).

Frequency of service.
The latest iteration of service adjustments now enables the SHARL to have 56 daily trips (and vice versa) with a 30-minute headway [4].This frequency marks a drop from as many as 82 daily trips allocated for both directions in early 2018 [22].Nevertheless, a recovery from a neartotal termination of services during the pandemic era should be appreciated.In addition, the current frequency and headway can be maintained throughout the week.However, as marked by the DGR load factor data, the weekday occupancy level is higher than the weekends.The operating hours of SHARL should also be reconsidered as they hinder the late night and early morning passengers (and airport workers) from using the service.

5.3.7.
Other aspects of service.Since early 2022, the SHARL introduced "premium class" trains on selected schedules.Initially trialled for just one month during the Covid-19 restrictions in April 2021, the premium class is still available with reduced fares on ten daily trips, and vice versa [4].A review of the trial period noted an increase in ridership due to a larger capacity seating arrangement being introduced [23].Another notable observation is the SHARL's higher ridership on weekdays than at weekends.Some possible explanations might be concluded: the business air passengers mostly travel on Mondays through Fridays, and the workers choose to ride SHARL whether or not they work at the airport.Hence, defining the appropriate market segment to be served by SHARL adds up to another task for its operator.Finally, the most considerable change during the first five years of SHARL operations is the transfer of the operating company from PT Railink to PT KCI [24].Now under the same management as the KRL Commuter Line, it follows Hong Kong's MTR precedent, which operates both the subway and the Airport Express, thus supplanting the airport rail link with an extensive network of commuter or mass rapid transit system.

The future of SHARL
The Directorate General of Railways is planning to reopen the Bekasi extension of SHARL, yet with an additional stop at Jatinegara station [4].Another plan is to establish a new route which branches towards the north at Duri and heads to Kampung Bandan and Pasar Senen stations (refer to Figure 3).The resumption of service towards Bekasi via a southern route may be considered due to the still ongoing double-double track improvements between Manggarai-Jatinegara-Bekasi and the upgrading project of Manggarai station, which are expected to complete as early as 2024 [2].Nonetheless, if the new northern route is to be constructed, a thorough planning of the development of railway facilities throughout the corridor is required since the "Eastern line" of Jakarta railway loop also serves as the freight train route towards the Tanjung Priok harbour.A far more important consideration is that operating the two planned SHARL routes in the future would make them completely overlap with the current Bekasi/Cikarang KRL line.Analysing how the Commuter Line demand will respond to service adjustments after such decisions shall be prioritised.Despite the necessary operational adjustments and physical improvements to enable a seamless connectivity between SHARL and other modes, it is imperative that other aspects of intermodal integration-such as legal/regulatory, institutional, informational, and economical/tariff aspects-need to be taken into account, which is a subject for further research.Ultimately, addressing these challenges will not only improve the efficiency and utilization of SHARL, but also contribute to a more sustainable and seamless travel experience for passengers.

Conclusions
In the analysis above, an assessment of SHARL's operational conditions and problems in the first five years of operation has shown that only four of the seven attributes have met what is minimally prescribed in the TRB study [5], which are the characteristics of the air traveller market, regional travel time, the extent of regional coverage, and frequency of service.However, room for improvement in the four attributes is necessary to boost the SHARL's ridership levels further.Furthermore, based on another TRB study [11], the operator's strategies to mitigate a low occupancy mostly fall under the operating or service adjustments category.In all fairness, a more comprehensive range of strategies, actions, or initiatives was limited because of the global pandemic during most of the five years.Despite plans for future service expansion by the DGR [4], which are also related to the same type of strategy, they lack a vision and clear strategy to fully integrate the SHARL service with other modes of public transportation in Jabodetabek.Such integration shall, in turn, pave the way towards higher ridership levels due to a more seamless transfer between the modes.The strategy to combine the SHARL and KRL Commuter Line operations under a single company in early 2023 has enabled "integration" in a business sense.Nonetheless, since the first day of SHARL operation, physical connectivity of the two modes has materialised with four of the five stops located at Jakarta's major rail interchanges.While it is still too early to conclude what PT KCI's takeover of the operation and the DGR's planning may bring about, the progress to an increase in SHARL's ridership is underway, along with the general transition from the pandemic to the endemic era.

Figure 3 .
Figure 3. Schematic map of Soekarno-Hatta airport rail link and other rail-based transportation lines in Jabodetabek region.The SHARL line is coloured orange on the map (Source:[4]).

Table A1 .
Some precedents of airport rail links in Asian cities