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
Abstract:
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
transport 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 |
Headway/Interval/Lanes |
Boarding time |
Berth number |
Terminals |
|
80 spaces bus |
4s/120m |
60¡120s |
40¡80 |
8¡12 |
|
40 seater bus |
2s/60m |
40¡80s |
54¡108 |
11¡15 |
|
20 seater |
1s/30m¡2s/60m/2Lanes |
30¡50s |
80¡135 |
16¡21 |
|
10 seater |
0.5s/15m¡2s/60m/4Lanes |
20¡30s |
108¡160 |
20¡26 |
|
7 seater car |
0.35s/10.5m¡2s/60m/6Lanes |
18¡25s |
135¡180 |
24¡36 |
|
5 seater car |
0.25s/7.5m¡2s/60m/8Lanes |
15¡20s |
160¡216 |
27¡40 |
|
2 seater car |
0.1s/3m¡2s/60m/20Lanes |
10¡15s |
270¡400 |
50¡68 |
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
|
LINE CAPACITY |
Effective traffic volume (vehicles/h) |
TERMINAL CAPACITY |
Embarking/disembarking capacity (vehicles/h) |
|||||||
|
Headway |
Capacity/ lane/h (vehicles/h) |
Number of the mainline lanes |
Berth arrangement type |
Number of berth |
||||||
|
2 |
4 |
6 |
10 |
4 |
6 |
8 |
12 |
|||
|
0.5 |
7200 |
7200 |
14400 |
21600 |
36000 |
Reversible |
360 |
540 |
720 |
1080 |
|
0.3 |
12000 |
12000 |
24000 |
36000 |
60000 |
Multi-series |
1200 |
1800 |
2400 |
3600 |
(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
|
Classification |
Comparative item |
SUBWAY (in Seoul) |
BT (estimated) |
Remarks |
|
Cost |
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. |
|
|
Fare |
$0.5 |
$0.5 |
For a distant of 10 km |
|
|
20km construction period |
60 months |
20 months |
BT: two elevated lanes |
|
|
Mobility |
Carrying capacity (ppdph) |
40,000~63,000 |
300,000 |
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) |
|
|
Accessibility |
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.
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Coping with traffic
congestion
When accident
occurs:
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