Case study: Displaying real-time bus occupancy levels in Seoul, South Korea

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Occupancy information on electronic signboards

South Korea and Seoul: geographic and demographic overview

South Korea is one of the world’s most densely populated and urbanized countries. Fully half the population of 50 million resides in the Seoul metropolitan region. “Smart City” has become a local buzzword, and the government continues to make rapid improvements in the quality of the urban infrastructure and environment. On May 22, 2017, real-time information displaying the level of crowding on Seoul’s city buses was rolled out across the network[1]. By utilizing existing data to enhance the service level, this update represents a textbook example of incremental innovation – improvements that could be accomplished without costly changes to the physical infrastructure.

Seoul public transport system overview

Seoul enjoys a world class public transport system. The urban rail system has 20 lines and over 500 stations. Buses play a vital role with a modal share of 27%, versus 39% for rail[2] In a massive public transport reform on 1 July 2004, bus routes were re-numbered according to the geographical start and end points and divided into clear color-coded categories:

  • Trunk lines for inter-regional (red buses)
  • Trunk lines for intra-reginal (blue buses)
  • Feeder (green buses)
  • Circular (yellow buses)

The reform also aimed to better integrate the infrastructure and service levels. Bus routes were reorganized to facilitate subway transfers, and exclusive median bus lanes (BRT) and improved transfer centers were constructed.

Service layer: T-money smart card

The fare system was also overhauled to coincide with the launch of the T-money smart card (“T” represents “tech, transport, and touch”[3]). Previously, bus-to-bus or bus-to-subway transfers required a separate fare. This caused passengers to use sub-optimal bus routings to avoid transfers. Under the new system, up to four free transfers are allowed, giving passengers an incentive to find the routing and modal combination that minimizes travel time. This has the positive side effect of reducing strain on the system by minimizing the number of passenger-minutes spent in the system.

The T-money smart card has become an indispensable part of the service level transport infrastructure. An innovative “post-paid” billing service launched in 2013 links the card to a user’s credit card and bills the monthly cumulative spending at the end of each month, thereby eliminating the need to top up the card. The T-money card can already be used in taxis, bicycle share and across most cities and regions of the country. It is possible that additional offerings such as car share and “all-you-can-ride” subscription plans will be added later. This would blur the line between a simple payment system and a true Mobility-as-a-Service (MaaS) concept, such as “Whim” by Maas Global, launched in Helsinki, Finland in 2016[4]

Data layer: Transport Operation & Information Service (TOPIS)

A robust data layer is crucial for the T-money system to function. Seoul’s Transport Operation & Information Service (TOPIS), also established in 2004, acts as the “control tower” for Seoul’s transport system by gathering and processing real-time traffic related information. Through its Bus Management System (BMS), it utilizes GPS receivers and wireless communication devices to gather and analyze bus information in real time. Major bus stops have electronic signboards displaying real-time information. Data is also made available through a public API, facilitating integration into smartphone apps.


Seoul TOPIS Bus Management System (BMS)
Source: Seoul Transport Operation & Information Service (TOPIS) [5]

Introduction of real-time bus occupancy-level information

On May 22, 2017, Seoul enhanced the quality of information provided by adding real-time occupancy conditions, which is determined by using data on passengers boardings and exists that is already collected for determining travel distance and transfer time.


Bus Occupancy Level

LevelGuide to level of congestion inside the bus
Seats are available
Standing passengers can each hold on to a handle
Passengers are crowding into the passageway and their bodies touch (abnormal)

Source: Seoul Metropolitan Government, Traffic news [6]

Discrepancies in accuracy of in real time occupancy information

The real-time occupancy information will not be entirely accurate due to several factors:

  • Cash fares: Buses in Seoul accept cash payment, and passengers paying by cash will not register in real-time occupancy statistics. However, the number of passengers paying by cash represents a small and declining proportion of total bus passengers.
  • Incomplete tapping out: Passengers are supposed to tap their smart cards both upon entering and exiting the bus (the 30-minute free transfer period is calculated from exiting the bus or subway gates). However, passengers sometimes neglect to tap out properly. Such passengers will incorrectly show up as present on the bus.
  • Fare evasion: A small number of passengers evade fare payment, and the will obviously not be reflected in occupancy information.

However, the level of inaccuracy from the above-mentioned factors is expected to average no more than 1-2 people per bus. Cash fares and fare dodging undercount occupancy while incomplete tapping out overcounts it, so the errors will be further reduced.


Real time occupancy information is provided for blue (trunk), green (feeder) and yellow (circular) buses. Coverage for red buses (inter-regional) and village (local) buses may be added in the future.  Occupancy information for M-bus routes (a special type of inter-regional commuter bus that does not allow standing passengers), has been provided since the launch of this bus type.

Information display method

Occupancy information is displayed on electronic signboards boards installed at major bus stops in Seoul in parenthesis following the route number.

Occupancy information on electronic signboards

English-language guide to the electronic bulletin board:

·        Route numbers displayed in white.

·        ETA displayed in blue on the right-hand side of the column (분 = minutes)

·        Imminent arrivals (within 1-2 min) displayed in the yellow box at bottom

·        Occupancy information displayed in parenthesis following bus number in imminent arrival box

o   Spacious (여유) in green

o   Normal  (보통) in yellow

o   Crowded (혼잡) in red

Image source: author’s own app screenshot


Occupancy information on phone app


Screenshot from Seoul public transport app (서울대중교통)

  • Screenshot shows a segment of the bus route 471
  • Blue boxes on the left-hand side depict individual buses and their current positions between stops
  • Occupancy information is indicated by the text on the right-hand side of the blue boxes.
  • Unlike electronic bulletin boards, text is not color coded – all three occupancy levels are displayed in yellow letters.
  • In this screenshot:
    • The top bus is at a “spacious” level (“여유”)
    • The bottom bus is at a “normal” (“보통”) level.

Image source: author’s own app screenshot[7]

Service level benefits of providing occupancy information: (Use case scenarios)

Access to real-time occupancy information enables passengers to adjust their journey plans in several different ways:

  • Wait for the next bus on the same route. Headways on trunk routes are often no more than 7-8 minutes. Elderly, mobility restricted passengers, or those traveling a long distance or who otherwise value a seat, waiting for the next bus may be worth-while.
  • Select an alternate bus route that travels along the same corridor. Alternatively, a one that follows a similar route.
  • Select the subway. For many origin-destination combinations, subways provide coverage (although usually with longer walking distances involved). The smoother ride may render standing less inconvenient on a subway, even if it is equally crowded.
  • Walk or bike the last mile. For short journeys (typically those connecting the origin or destination to the subway station) some passengers may prefer to simply walk or use the bike share scheme.


System level benefit: reducing “bus bunching”

Providing bus occupancy information may be helpful in reducing “bus bunching”: When the headway between the first and second bus on the same route increases (for example due to traffic congestion, the number of passengers waiting for the second bus will increase (assuming that passengers’ arrival times at bus stops is random and evenly distributed). Since each passenger boarding and exit takes a certain amount of time, the extra load on this second bus will slow it down further, narrowing the headway to the third bus on the route. Therefore, not many passengers will be waiting for this third bus, so it will travel faster than the second bus, and may even catch up with it.

However, with both real time arrival and occupancy information, passengers can see that the third bus is lightly loaded and only moments behind. Therefore, some passengers may let the second bus pass and wait for the third. With more evenly distributed loads, the difference in speed between the second and third buses will be reduced, thereby helping to maintain more even headway spacing.


This case study has examined the recent introduction of real-time bus occupancy information in Seoul, South Korea. It has shown such information represents a clear example of the “improve” pathway, as it results in a refinement of the user experience, safety and efficiency through incremental innovations. Only modest changes to the protocols used to process and distribute existing data were required. While it is out of the scope of this case study to provide a cost/benefit analysis, it is a reasonable assumption that the costs involved were modest compared to other changes to the physical transport infrastructure.

It should be noted that the ability to determine real-time bus occupancy data depends on passengers tapping their fare card both upon boarding and exiting the vehicle, which is already the case in Seoul. Therefore, providing occupancy data required no behavioral change from passengers. In systems where both tapping in and out is not required, gathering the data required would necessitate the installation of physical infrastructure (for example, sensors measuring passenger exits.) Thus, the immediate generalizability of this case is limited to systems that already require both tapping in and out.


[1]Seoul Metropolitan Government, Traffic news, “New service allows passengers to check congestion level of buses in Seoul”

[2]Seoul Public Transportation, Seoul Metropolitan Government

[3]OECD (2017), Urban Transport Governance and Inclusive Development in Korea, OECD Publishing, Paris

[4]Cities Today, “Finland launches first complete multimodal transport app”

[5]Seoul Transport Operation & Information System (TOPIS)

[6]Seoul Metropolitan Government, Traffic news, “New service allows passengers to check congestion level of buses in Seoul”

[7] Seoul Metropolitan government, official public transport app:

This piece is the original writing of the author(s). The view points in the post is the author’s personal opinions and do not reflect IGLUS/EPFL’s viewpoints. The author(s) is the sole responsible person regarding the accuracy of the information presented in the post and will be liable for any potential copyright infringements.

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