A High Capacity Transit of Structure for a High-Frequency Service

    Taejin Park email: btcom@korea.com   Dongho Choi, Ph. D.  email:kuuedhc@gwangju.ac.kr    Go to Paper in Korean


In a transport facility, such as a guideway, the more frequent vehicles operation leads to the more capacity and the better efficiency of the transit. The aim of this research is to find an efficient way to increase this service frequency. A highway is one mode of transport that runs at a high frequency, and has the structural characteristics that make nonstop, high-speed running possible. A guideway transit that has a structure and character similar to that of a highway, a frequent service is possible by nonstop running. The structure of the guideway for a frequent service in urban area needs a simple interchange structure with a large turning radius, and a terminal structure with a high handling capacity. A guideway transit with these structures in place can transp
ort a large volume of passengers through frequent service. A guideway transit system of this type can carry 36,000~300,000 passengers per hour comfortably and swiftly.

1. Introduction

  Traffic congestion may be largely relieved if the carrying capacity of public transits is increased. An increased service frequency is an effective method of enlarging the passenger carrying capacity. For this reason, various structural improvements have been tried, by designing multiple arrangements of platforms, by the addition of paths, and by speeding up traffic flow along paths.

The aim of this research is to find an efficient way to increase this service frequency. A highway is one mode of transport that runs at a high frequency, and has the structural characteristics that make nonstop, high-speed running possible. Frequent servicing is possible on a guideway that has a structure similar to a highway. This research has investigated a guideway structure as a frequent service model, and has examined the possibilities of achieving a more frequent service.

This paper proposes a guideway system that is similar in structure and characteristic to a highway, and assumes the possibility of high-frequency service in this guideway transit, with a high transit capacity and passenger convenience.

2. A Structure for High-Frequency Service


    2.1 Berths layout
    If we assume that there is the same running frequency within the guideway as there is on a highway, and then the most serious problem will occur when a number of vehicles try to stop. The vehicles will have many different destinations, and on reaching any particular station, some will try to stop; however, the most will pass through at the driving speed. This is similar to a situation encountered at a highway interchange, and if the guideway has a similar structure to a highway as shown in Figure 1, the stopping vehicles can enter a branch line and the passing vehicles can then keep to the driving speed.
    Figure 1. Branch-line structure and Terminal structure.

    The next problem is to safely alight from or ride in, one of the many vehicles entering a branch line without causing any traffic congestion. If there is only one berth, only one vehicle at a time can enter during the period spent in completing the action of alighting from (or riding in) a vehicle, and the next vehicle can only enter after this.


    Even if there were many berths in series, the alighting capacity cannot increase in proportion to the increase in the number of berths. If the berths are arranged in rows, as in Figure 1b, initially, as many vehicles as there are numbers of berths can stop for an alighting time. In theory, if the time spent on the passengers' alighting needs is less than the time spent in controlling the vehicles, and if there are no other barriers to alighting, then, say for 40 berths, 4,800 vehicles per hour may stop with an assumed alighting time of 30 s (i.e., 40*[3,600 / 30] = 4,800). However, there is a problem in that the 40 berths will occupy too much space. Nevertheless, if they are dispersed into many terminals, as shown in Figure 1a, then these may be cleared, and the passengers' accessibility can be improved from the number of locations. In addition, dispersed terminals mean that the size of terminal can be reduced so that a terminal can be installed in existing buildings, such as department stores, airports, and schools and also existing parking lots can be utilized. New terminal buildings may also be constructed at selected locations. In this case, a guideway should be established as a two-level structure for both directions. Then the whole of the guideway lines can be structured as a one-way road. This will make it easier for diverging toward each terminal. It will also be possible to provide a nonstop service for straight-on journeys to their destinations without making any intermediate stops, since all the terminals and all the berths are arranged in rows, heading for the mainline.

    According to the rate of boarding and alighting, 50 ± 25 % of the 40 berths in a branch line will be in use when the traffic is heavy, so this structure of arranging the berths in rows has a theoretical service interval (headway) of 1 s (i.e., 4,800*0.75=3,600 alighting/boarding vehicles per hour).

    Figure 2. Cubic interchange

    2.2 Simple Interchange Structure
    An urban expressway and highway interchange consists of ramps with a small radius, or a complex structure for turning left, which uses large areas of land in order to increase the turning radius. If a two-level guideway is built, then turning left is easily archived as turning right. This enables easy branching and is a simple structure. The simple interchange structure of Figure 2 is one using the easy branching of a two-level guideway, in which left-turning branches turn into the left side, and right-turning branches turn into the right side. The turning radius is therefore large, and the structure becomes simple.


    Figure 2 shows how the two pairs of ramps are connected, crossing from the upper to the lower level, (by way of the twisted ramps in Figure 2a) so that any conflicts that may arise from opposing directions are removed. As this simple structure occupies less construction space than that of a highway interchange, it is possible to construct this type of interchange at every crossing point of the guideway and in urban areas. Moreover, it makes it possible for the guideway transit for nonstop running the same as that of a highway. A three-way interchange will look the same as one half of Figure 2 (i.e., as shown in Figure 2e).

    On establishing a roof and walls on the top story guideway (the downstairs guideway will already have a roof and walls), the guideway cross section will have the shape shown in Figure 2c. The roof will lessen the influence of weather. The interchange shown in Figure 2b would be established at the crossing of a broad road, as an elevated (or underground) construction, so that passing speed of ramps can be designed to high, using a large turning radius as in Figure 2d.


3. A High-Frequency Transit Service

    3.1 Formation of a Transit

    Connecting a simple interchange with a large turning radius to a mainline and a branch line of a two-level guideway, and can make a guideway with a similar structure to that of a highway by connecting to terminals with large alighting capacity. If human drivers drive vehicles using nonstop high-speed driving without any automatic control device, then the additional facilities must be installed on the guideway, such as speed limitation measures, speed-change lane, signposts, and mileposts. In this case, the transit can achieve a high-frequency service, similar to the level achieved on a highway. This has merits, such as nonstop, high-speed traffic flow, improved accessibility, and comfortable travel.

    If the vehicles are driven automatically, instead of drivers, and are controlled safely, then a higher-frequency service is possible by shortening the gap between vehicles. This would differ from the highway situation. Shortening vehicle gap by three times will increase the capacity and efficiency to 3 times that of the highway. In general, shorter gaps will increase capacity, but longer gaps will increase safety and ease of control.

    Mainlines will be built in urban areas in the center of existing wide roads, with the interchanges having large radius ramps. This arrangement takes advantage of the straightness of mainlines to achieve high running speeds: the straighter the lines, the better the design for rapid speed. The terminals should be installed at a distance far enough from the interchange for adequate acceleration/deceleration.

    For example, assuming that two branch lines with six dispersed terminals are directly connected through round-trip lines between cities 5~150 km apart like Figure 3b for intercity travel, then vehicles will be operated in less than 10 branches with fewer than 10 merges, so the control system will be simple, and a frequent service will be readily attainable.

    Figure 3. Various formations.

    If a 20-seater vehicle as in Figure 3d departs for a destination terminal every 72 s from a berth, as in Figure 3c, then another five vehicles will depart to another five further destination terminals from an origin terminal every 72 s. The vehicles can then depart every 12 s sequentially from an origin terminal. Further, if these vehicles depart from the six origin terminals sequentially, as shown in Figure 3b, then the vehicles will run every 2 s on the mainlines sequentially, and carrying capacity will be 36,000 ppdph (passengers per direction per hour) (20 seater*3600 s/2 s).

    The speed of mainlines should be a sustained 108 km/h (30 m/s). A typical mainline is from points p1 to p6 in Figure 3b. In this case, the operating interval between vehicles will be 60 m (30 m/s*2 s - a relative safe interval). Vehicles must depart just in time to reach point p5 from each of the origin terminals in order to meet the correct running order at point p5.


    If the vehicles are 40 seater, then the carrying capacity will be 72,000 ppdph, or an operating interval of 120 m can be used. Therefore, it is possible to tailor the composition of the transit to fit the carrying capacity. The guideway structures described in the previous section are efficient for high-frequency service, and their higher carrying capacity means they can provide an effectual increase in this area. At constant speeds, a 60 or 120m interval will be safer than on a highway.

     However, in off-peak hour, scheduled services will be reduced, e.g. only six destination terminals may be desirable for operational convenience. When the number of passengers is insufficient, the above scheme can be serviced intermittently, according to passenger volume. The number of terminals and branch lines can be increased and guideways to other directions can be extended through interchanges. Figure 3e shows an extended shape to 12 origin terminals and 12 destination terminals. In this case, six of the terminal berths would indicate alternate double destinations. A small-sized terminal using only two berths would indicate sequentially 12 destinations on the departure berth.

    If the number of destination terminals is large, then vehicles with a small number of seater will be more efficient. At the departure terminal, vehicle distribution will be spread amongst the more demanded destination terminals. Figures 3f and 3g show that this can be established in a wide area, using interchanges and extensions of the guideway and branch lines.

    A frequent nonstop service to various destinations as an on-demand service will be required mainly 1~2-seater service by vehicles having a sole occupant. In practice, five-seater (or seven-seater) cars are smaller and lighter than vehicles with many seater, and therefore, the guideway will be constructed at a lower cost and with a smaller size, and this facilitates an elevated construction. More small seater car will make occupant rate high, waiting time short and convenience high. A five-seater car will have low noise and vibration, and will need a small-sized terminal. It should be possible to have vehicles merging and branching, and for automatic driving. If this is possible, then any type of powered vehicle can be used.

    3.2 Conditions for High-Frequency Service

    Using high technology, the vehicles can run automatically on installing an automatic driving device. Similar modes of operation have been shown to be possible, such as automatic guideway transits (AGT) or in present car cruise-control systems.

    A high-frequency service here would be limited by the handling capacity of the terminals, by the admission capacity of the mainlines, and by the limitations in control techniques. The speed is decided by the lower value between that of the curvature of the guideway and the maximum speed of the vehicle. Enough guideway levels can be achieved by increasing the number of lanes, and by increasing the number of terminals. The guideway curvature and vehicle speed can be satisfactorily set to 100 km/h. An effective control system should be developed for safety, and to increase the efficiency of the frequent service.

    It has been difficult to realize a frequent-service guideway transit, not because of a lack of control techniques, but rather because of the guideway structure itself. This paper proposes such a structural possibility, so that hereafter, any additional debate can be carried out based on an expected vehicle speed of 30 m/s (108 km/h), and adequate control.

    The guideway floor involving the merging and branching should be flat, and the tires of vehicles should be made of rubber. The vehicles should then run along a pilot line (traveling line) after following a line in the center of the guideway lane. Vehicles should travel on a single pilot line selected from the many pilot lines at the merging and branching points, or when changing lanes at a multi-lane section; the latter will only be installed in locations with a large demand in passing capacity.

    The high-frequency service will have physical limitations (velocity/vehicle length). If one assumes that a five-seater vehicle is 4 m in length, and has a speed of 30 m/s (108 km/h), then by considering the linearity of the mainlines, the turning radius of the interchange ramps, and the output speed of the vehicle, then the theoretical minimum headway will be about 0.15 s with ample alighting/boarding capacity. However, 0.3 s will be the realizable minimum. A 0.37 s headway, using automatic control, was realized on 7-10 August 1997 on 15 express lanes in San Diego (105 km/h, 6.5 m gap, 7 cars platoon.) (Shladover, 1997).


    3.3 The Control System

    When a passenger enters a terminal and selects a destination through ticketing, he or she will receive a ticket with a berth number and boarding order on it. The in-terminal computer in the terminal calculates course and time to the destination.

    The in-terminal computer transmits the route data regarding the direction that should be selected and every branch point on the route to the in-vehicle computer through photo couplers, and indicates the ticket number for the passenger. A vehicle starts at the time of that can merge to mainline safely after passenger gets on. The vehicles run along the pilot line, using set values to control the angle and the speed of acceleration, the constant speed and the deceleration. When it is reached branching points, the vehicle steers in the direction received before the trip began, and passes the merging points, until the journey's end is reached.

    When the vehicle enters to the destination berth, and after the passenger alights, the vehicle moves at low speed, using the received ¡®inner terminal route data¡¯ from the in-terminal computer to go to an equipment bay, a car wash, a parking lot, or to an entrain-berth, depending on a self-diagnosis of the vehicle. Empty vehicles should go to the terminal and be ready for occupancy, and the empty vehicles should be run on the route data from the in-terminal computer.

    While minimizing the possibility of accident through periodic equipment checks, a wrecking car should be prepared in case of any incidents. All vehicles would be equipped with infrared sensors to enable safe signaling.

    If there is excess guideway capacity, and the guideway has a safe merging structure at an acceleration section (i.e., merging with a similar highway structure to it), then a high-frequency service will be possible. Each vehicle would be controlled individually when passing branching and merging points. If one vehicle is present in the lane another vehicle wishes to enter, then the merging vehicle should enter into the lane in front of (or to the rear of) the first vehicle. After the lane change, the vehicle that has changed lanes and front/rear vehicles should adjust their speed and interval to that which must be maintained for safe running.

    The vehicles must be tightly controlled in the departure terminals to prevent arrival congestion through communication, but the guideway capacity should be such that no overcrowding occurs. If this does arise, then it should be solved as for a highway, and the departure of the vehicles will be controlled. The scope of the congestion will be limited to no excess of the total number of vehicles.

    3.4 Effectiveness

    If there are 40 berths in a branch line, and a vehicle departs each 30 s from 30 of these berths, then the capacity of the branch line is 3,600 vehicles/h (1 s headway). Therefore, the Branch-line Transit (BT, hereafter, BT) with 100 branch lines (4,000 berths) can theoretically transport a maximum 900,000 ppdph (assuming half are boarding) by 5-seater car.

    If the target capacity is 72,000 ppdph that is larger than 40,000~60,000 ppdph of subway (Won, 1987, Rhee, 1998), but it can satisfy any required capacity, and mainline speed is 108km/h (30m/s), then vehicle size is selected among the various size.

    Table 1 Variety of elements by seater size

    Seating capacity


    Boarding time

    Berth number


    80 spaces bus





    40 seater bus





    20 seater





    10 seater





    7 seater car





    5 seater car





    2 seater car





     The seater size will be decided by three factors, cost, convenience (waiting interval and destination variety), and safety running interval. Buses have low convenience and high cost, but safety interval is good. A 0.5s headway automatic driving on the guideway can realize with the lower cost then 0.37s headway on the expressway. Cause automatic driving will make construction cost low, convenience up, operation cost reduces, and so optimum control system will be developed.

    Capacity in table 1 is in proportion to seating capacity, lane number or berth number, and is in inverse proportion to headway or boarding time.
    C¡ðSL/H, C¡ðSB/t            (1)
    C: Capacity, S: Seater, L: Lane number, H: Headway, B: Berth number, t: Boarding Time.
    On the upper equation, it shows that shorten boarding time or headway make cost down and efficiency up.

    Personal Rapid Transits (PRT), (SkyTran (SkyTran, 1999), PRT2000 (PRT2000, 1999)) in various Automated People Movers (APM (ITT, 1995)) achieves frequent service with an off-line stop method. However, their stations have little berths arranged in series, and the alighting capacities of their stations are small. Since the transit capacity is in proportion to the number of berths in this method, and then capacities are small.

      Table 2 Expected line capacity and alighting capacity of BT


    Effective traffic volume (vehicles/h)


    Embarking/disembarking capacity (vehicles/h)


    Capacity/ lane/h (vehicles/h)

    Number of the mainline lanes

    Berth arrangement type

    Number of berth































    (If 5 seater cars are used, the capacity is 36,000~300,000 persons/h)

     In Table 2, a boarding/alighting time of 30 s is assumed, and the terminal capacities were calculated as being 75 % of the number of berths multiplied by 120 vehicles per hour. These 'reversible'-type berths can be converted between functions in accordance with the ratio of the loading and unloading capacities, as shown in Figure 1b.
    In the 'multi-series'-type berths, two to four vehicles can berth at the same platform in series. This large capacity type will be used in locations needing short durations or when demand is high, such as in movie theaters, sports stadiums, schools, or in large buildings.

    If the capacity of a highway is 2,000 vehicles/h, then this elevated guideway can transport more than 6 times the above. During rush hour, the vehicle will be distributed after four to five passengers have received tickets for the same destination. The BT mainline can be constructed as a mesh by using miniaturized interchanges, and, in urban sections, will be built as multiple lanes to service large volumes of traffic. Table 3 shows the forecasted result of the BT. 

    Table 3 Comparison of characteristics


    Comparative item

    SUBWAY       (in Seoul)

    BT (estimated)



    Weight of train/vehicle

    300~430 ton

    1 ton

    Reduced by a factor of 300

    Construction cost per km (whole costs)

    $60 million

    $8 million

    BT: two-lane elevated.   Subway in USA was $ 40~105 million.




    For a distant of 10 km

    20km construction period

    60 months

    20 months

    BT: two elevated lanes


    Carrying capacity (ppdph)



    BT: maximum of five lanes per direction

    Travel speed per hour

    35 km

    102 km

    Subway: 31.2~35.9km/h

    Peak hourly volume (Throughout the whole of Seoul)

    420,000 persons

    1,800,000 persons

    Subway: 7 lines (218km)          BT: 600km (total length)


    Number of stations/terminals

    197 each

    800 each

    Four times including various and direct

    Distance between stations

    1,100 m

    500 m

    Point at which traffic occurs.

      The data assume that the procedure of the BT is stabilized, and that the BT is established instead of the current subway in Seoul. (The current population of Seoul is 11 million) If a five-seater vehicle weighs below 1,600 kg, and the guideway is constructed as an overhead system, then the construction costs will be sharply reduced when compared with a subway system. We propose that such a facility can handle one million passengers per hour, and that a 600-km guideway shall be constructed for 4,800 million dollars.
    For an average fare of half a dollar, we estimate that an average of 14 million passengers per day will use the system, including small freight items. This will amount to 5,000 million per year, with an annual gross product of 2,500 million dollars. Thus, the BT annual receipts are around 50 % of the construction costs. Therefore, the construction costs can be repaid rapidly, or the fare costs could be reduced to less than a quarter of a dollar.

    The BT is a variable capacity transit, meaning that it has a different number of lanes. So theoretically, five lanes per direction can carry 300,000 ppdph in the required section, and in most sections, including the branch lines, about 80 % of the guideway will be built as two lanes in both directions. The BT can be operated using only two branch lines, can add further terminals, branch lines, and mainlines on demand.

    The BT has disadvantages in requiring many vehicles, which have individual energy consumptions, and it needs additional construction for the branch lines. However, it will have the advantages of nonstop high-speed motion, comfortable seating, on-demand service, improvement in accessibility, private travel, and the possibility of a high net profit from frequent use, or a low fare arising from the low construction costs in combination with its large traffic capacity.


4. Conclusion

The carrying capacity is the most important component in any future transit system. The carrying capacity of the guideway transit system presented in this paper can be enlarged effectively by increasing the service frequency.

This paper has investigated a guideway structure that is capable of providing a high-frequency guideway transit service. The result of this investigation is as follows:

This guideway transit has a structure of established terminals on the branch lines only and not on the mainline. This makes nonstop running possible and the dispersed terminals in several places on the branch line lead to an improvement in accessibility. A multi-parallel arrangement of berths on the branch line makes a high-frequency service possible.

Both direction of the guideway are located in a two-level arrangement, this leads interchange structure simple. This is useful in reduced space environments such as in urban areas, and the large radius ramp enables design speed high.

The flat floor of the guideway structure means that activities such as branching, merging and changing lanes are easy, as for automobiles, and it enables all sections of the guideway to be designed with sufficient capacity. This can be achieved by the establishment of multi-lane sections in urban districts where traffic volume is expected to be large.

These guideway have a theoretical structural headway service below 0.3 s. If a safe and effective control system is supplied, then a large volume of transport will be possible through high-frequency service.

In the future, transit system of this type has the potential to comfortably and swiftly convey to 300,000 passengers per hour. With further efforts in simulation, development, testing, and optimization of design, the most efficient and economical use of this system should be realized.


Innovative Transportation Technologies (1997) http://faculty.washington.edu/~jbs/itrans

PRT2000 Concept Page. (1999). http://faculty.washington.edu/~jbs/itrans/PRT/PRT2000_Concept2.html

Rhee, Jongho. (1998) 'Points to be considered when medium capacity transits are introduced' Journal of Korea Society of Transportation. Vol.16, No. 4, pp. 249-264

Seoul Subway Corporation. (1997). Seoul Subway Vehicle Important Feature. http://www.seoulsubway.co.kr/

Shladover, Steven. (1997) AHS Demo ¡¯97 ¡°Complete Success¡±. Intellimotion Volume 6, No. 3.   http://www.path.berkeley.edu/PATH/Intellimotion/intel63.pdf

SkyTran, (1999) SkyTran Offline Portals. http://www.skytran.net/01QuickTour/qt02.htm

Won, Jaimu. (1987) ¡®A Theory of Urban Transportation¡¯. Bak-young sa. pp. 366~390.

Signal systems Coping with traffic congestion
  • Reason for having no congestion
    1.Vehicles operate below capacity
    2.There is ample guideway space (facilities)
    3.There is a wide enough gap
    4.There is ramp metering


  • When congestion occurs
    Distribution control for congested area

When accident occurs:
1.The vehicles stop using safe signaling (by infrared sensor)
2. The speed is reduced by beacons (used for reporting or detecting)
3. The numbers entering the accident area are limited.
4. The wracking takes place upstream.
5. The operation of the system is resumed.