This article explains some technical developments in speed
increase until the opening of the shinkansen in 1964, centred
on lines belonging to JR companies (formerly Japanese National Railways or JNR).
Increasing Speeds on Conventional Lines
Non-shinkansen lines (often including non-JR railways) in
Japan are commonly called conventional lines. Japan is a
mountainous country, and most conventional lines were built
to the narrow gauge of 1067 mm, but some private lines
use standard gauge (1435 mm). When trying to increase
operating speeds in the era of stream-hauled trains, narrow
gauge proved to have intrinsic disadvantages and the many
curves and grades in Japan’s mountainous areas also hampered speed increase.
Against this background, electric trains—especially
electric multiple units (EMUs)—seems to offer the greatest
potential for increasing speeds, because the distributed
powered axles along the train length had advantages in
reducing axle load while increasing tractive effort as a
whole. Efforts were made in electrification of railways for that
reason, but there were few developments on major trunk
lines before World War II at the request of the military. As a
consequence, major speed increases were only achieved on a wide scale as postwar electrification proceeded.
Speed constraints on conventional lines
Trains on conventional railways (including both JR
and non-JR lines) face the constraint of a maximum
emergency braking distance of 600 m. In the early days,
this distance was considered the distance at which
signals could be surely seen by train drivers. But today it
is to ensure the ability of a train to stop in an emergency
on a line with level crossings. This 600-m limit imposes a
maximum speed of 130 km/h due to physical constraints
such as loss of adhesion between steel wheels and rails
at emergency braking. On lines without level crossings,
maximum speeds up to 160 km/h are permitted on an
exceptional basis. Europe does not have such constraints
and 160 km/h is the normal maximum operating speed on non-high–speed lines.
Increasing speeds on conventional lines
In a nutshell, the history of railway technology is the history
of increased speeds and enhanced transport capacity.
Looking at the example of the Tokaido Line, Japan’s main
trunk line, many modifications were constantly being made to
shorten the travel time between Tokyo and Osaka. Even so,
the maximum speed up to the 1950s was 95 km/h. However,
electrification toward the end of this era made it possible to
shorten journey times without increasing maximum speed (Figure 1).
The limiting factors were the tractive power of steam and
the weak ground under the roadbed, which limited maximum axle loads. For comparison, on the standard-gauge South Manchurian Railway, operating speed of 110 km/h was attained by express trains built in 1934 using Japanese technology. Some speed increase with electric locomotives was possible by electrification, but electrification was not popular for various reasons.
EMUs, which were mainly used for commuter traffic
in those days, ran short distances and stopped at many
stations, so increasing maximum speed had little effect on journey times. However, in the 1930s, government railways
competed with private railways in a contest of increased
speeds. After WWII, in the late 1950s, the influence of
American technologies developed for PCC car finally
reached Japan, and improvements were made mainly in
acceleration and deceleration. Such new technologies,
coupled with the advantage of light axle load, contributed
to the development of high–speed EMUs for intercity
services, reaching maximum speeds of 110 km/h first and then 120 km/h.
With an eye to the future, JNR’s chief mechanical engineer
Hideo Shima (1901–98) established a study group on high–speed
bogie vibration in 1947 and started research into
speed increases. Shima was a specialist in steam locomotive
design. He believed that it would be difficult to increase
speeds of loco-hauled trains with their heavy axle loads even
on standard gauge tracks due to Japan’s topographical and
geological nature. He realized that increasing the speed
of EMUs with light axles was the key, and started work on
developing high–speed bogies for EMUs.
In 1948, a 1930s Moha 52 EMU reached a maximum speed of 119 km/h
and then a new EMU belonging to Odakyu
Electric Railway set a speed record of 145
km/h on the Tokaido main line in 1957. In
1959, a test run using Series 151 EMU
reached 163 km/h, followed by a high–speed
test car setting a narrow-gauge
world record of 175 km/h in 1960. The
results of research into high–speed bogies
were utilized in developing high–speed
intercity EMUs such as Series 151, and
also became the development foundation
for shinkansen high–speed bogies.
The Series 151 EMU, which attained 163 km/h in 1959, was used for limited
express services between Tokyo and
Osaka. Inaugurated in 1958, it ran 556 km
between the two cities in 6.5 hours. This
epoch-making EMU was welcomed by
society as a whole and had a major impact on development of the shinkansen.
|Figure 1: Speed Increase on Tokaido Main Line
Photo: Kumoya 93 High-speed Testing Car that Set a Record of 175 km/h (100 Years of JNR Rolling Stock)
Photo: Moha 52 EMU Produced in 1936 (100 Years of JNR Rolling Stock)
Measures to increase speed of conventional lines
The success of the long-distance EMU
service between Tokyo and Osaka spread
to other intercity routes across Japan. Many
of those were achieved thanks to expansion
of main line electrification. Much of the new
main-line electrification used alternation
current (AC), so many long-distance dual-current EMUs were
built to run through both AC (20 kV, 50/60 Hz) and DC (1.5 kV) sections.
Maximum speeds reached 120 km/h by the late 1960s,
but these trains had almost reached their limits in terms of
the constraint of emergency braking distances of less than
600 m. The maximum speed could only be increased to
130 km, even using anti-slip re-adhesion techniques. Later
running tests by the Railway Technical Research Institute
(RTRI) and JR Shikoku verified that maximum speeds up 160
km/h were possible using rail braking, which were common
in the USA and Europe at that time, but rail braking was not
put to practical use in Japan for various reasons.
Japanese railways are characterized by many curves
and grades, so increasing the maximum speed was ineffective in reducing travel time on most inter city routes.
To reduce travel times, the speed in curves and on grades
had to be increased, not the maximum speed. As a result, the development of tilting trains started in the late 1960s.
Development of Shinkansen
Measure to increase capacity on Tokaido main line
The rapid postwar recovery led to increasing traffic
volumes, and insufficient rail transport capacity soon
became major bottlenecks for Japan’s economic
development. Above all, by 1955, the Tokaido main line
was facing such severe lack of capacity that another
double-track was thought to be necessary.
A committee was created in 1956 to investigate how to
increase capacity quickly, and measures such as quadruple
tracking or building a new line were discussed. Opinions
were split, and the easier measure of adding track held the
advantage. However, decision by Shinji Sogo (1884–1981,
appointed JNR President in 1955) to throw out the old
concept and create a more rational system led to favouring construction of a new separate line.
|Photo: New RTRI building Completed in 1959 (RTRI)
Photo: Shinkansen Test EMU and JNR President Sogo (History of Technical Development of Tokaido
Ideas for the Tokaido Shinkansen
The quickest and most economical way of building a new
line along the Tokaido route was to utilize the land purchased
and partially constructed tunnels for the so-called ‘bullet
train’ project abandoned in 1943.
The outline of ‘bullet train’ plan is as follows: The preliminary survey started in 1938. Construction
specifications decided in 1941 settled on building a doublet–rack
with a gauge of 1435 mm, minimum curve radius of
2500 m, maximum grade of 10 ‰, maximum axle load of 28 tonnes, and 60 kg/m or heavier rails. Partial electrification at 3 kV dc was planned. The rolling stock gauge (loading
gauge) was set at maximum height of 4800 mm and
maximum width of 3400 mm. All trains were to be hauled by
locomotives, running between Tokyo and Osaka in 4.5 hours
at speeds up to 200 km/h.
Purchase of land started in 1939, and tunnel construction
started in 1941. Construction was abandoned in 1943 due to
worsening war situations.
Sogo proposed construction of a high–speed new line
in 1957, and the government set up a Ministry of Transport
(MOT) panel to investigate the idea. Around the same time,
RTRI presented a lecture on the technical feasibility of rail
travel between Tokyo and Osaka in 3 hours, and awareness
of high–speed rail spread to the public.
The MOT panel conducted detailed deliberation of the
high–speed new line, and the shinkansen plan was finalized in 1958. It followed the prewar bullet train project in many aspects, including the route and technical specifications such as 1435-mm gauge track, minimum curve radius of 2500 m, and maximum grade of 10 ‰. The new plan targeted 3-hour journeys between Tokyo and Osaka using EMU trains on an AC-electrified track. The construction period was 5 years. The framework was approved by the Cabinet and the plan was put into action in 1959. JNR set up a committee in 1958 led by Hideo Shima, who was appointed to JNR Vice President for Enginnering in 1955, to investigate construction standards that were given provisional MOT approval in 1960 and officially adopted in 1962. Construction started in 1959, and the Tokaido Shinkansen was completed in 1964.
Sogo did more than just decide on the construction of
a railway with a new system. While not an engineer, he had
excellent knowledge of technical subjects, and he made
the decision in 1956 to provide massive funding to the RTRI
to provide better research environment. One of the results
was the aforementioned lecture, which is thought to have
garnered great support for Sogo’s decision.
As an aside, two German high–speed test train cars
are famous for having reached 210 km/h in 1903. Those
were special test cars that collected three-phase AC power from three pantographs, and the rotating speed of 3-phase asynchronous motors was controlled by changing
the frequency at substations. The system did not come
into practical use due to technical requirements, but
achieving speeds in excess of 200 km/h at such an early
date was revolutionary. While it may be only a coincidence,
Yasujiro Shima, leading mechanical engineer of Japanese
government railways, was at the test runs. Perhaps the
prewar bullet train project headed by Shima was influenced
by his witnessing the tests and it is fitting that it was his son
JNR Chief Engineer Hideo Shima who was responsible for
building the Tokaido Shinkansen running at 200 km/h some 60 years later.
|Photo: Shinkansen Bogie Tests on a Rolling Stock Test Stand (RTRI)
Figure 2: Series 0, 100, and 200 Running Resistance Comparison (Outside Tunnels)
Shinkansen Technical Issues and their Solutions
While 160 km/h was a common speed in North America
and Europe, there were worries about speeds in excess
of 200 km/h in those countries. Although the German AC
powered test trains described above reached 210 km/h,
it was a struggle to overcome the technical barriers.
Another test train set a record of 331 km/h in France in
1955, but limitations pertaining to stable running and power
collection performance were highlighted. We can assume
that challenging technical innovations were thought to be necessary to go any faster.
Aeroplanes and automobile expressways were also
developing rapidly during this time period and the popular
feeling was that the age of rail was coming to an end, so the
motivation to seek innovations in railway technology could have been declining.
Construction of the Tokaido Shinkansen started amidst this social background. There was no technology anywhere
in the world offering day-to-day stable operations at speeds
greater than 200 km/h, although the Japanese engineers
had some vague knowledge of the results of the French
high–speed tests. They rose to challenge of exploring the
unknown ‘territory’ of high–speed operations. The following
looks at their major accomplishments on the path to solving the many problems.
Issues with traction power and axle load
The basic issues for high–speed operation are securing
power source and transmission of tractive effort. Running
resistance increases at roughly the square of speed,
requiring enormous power for running faster trains. Adhesion
between rails and driving wheels transmitting the tractive
effort also becomes a problem. With a conventional loco–hauled train, this can be overcome by making the locomotive heavier but the high axle loads of heavy locomotives require solid and sturdy tracks that are expensive to build.
Building such tracks on the weak ground along the Tokaido
Shinkansen would have been extremely difficult.
AC electrification was a solution for providing trains with
greater power. Electric power supplied at very high voltage
could greatly reduce the current required for high–speed
running, facilitating power collection by trains. Japan had
just acquired the technology of AC electrification on its own
account in the late 1950s.
The solution to heave axle loads was switching to
EMUs with distributed motive power along the train length
producing high traction effort and lower axle loads.
Advances in semiconductors for power supply during the late 1950s supported development of AC EMU trains.
Securing high–speed running stability
The issue of securing running stability was behind the
difficulty in reaching 210 km/h with the German test train in 1903 so track and bogie modifications were made to conquer hunting oscillation. The 1955 high–speed tests in France also experienced serious hunting oscillation, leaving the track very deformed after the test train had passed by.
In light of these tests, some technology was needed
to prevent hunting oscillation of
shinkansen running at commercial
speeds and this proved to be the
most important issue in developing
shinkansen technology. Hunting
oscillation is inevitable with railway
cars due to their structure, but it
can be avoided if the speed range
in which hunting occurs could be
made higher than operating speeds.
However, the methods known at that
time was not appropriate for high–speed bogie design.
A main theme of the study group
on high–speed bogie vibration was
bogie hunting, and research was
already in progress. Theoretical
analysis and experiments were done
mainly by aeronautical engineers who
had transferred to the RTRI from former
imperial navy research labs. Bogies were designed and
redesigned for repeated tests using prototype bogies on a
test stand at RTRI and prototype rolling stock on shinkansen
test tracks. As a result, hunting was not a problem when the
shinkansen opened at maximum operating speeds of 210
km/h. However, some signs of hunting were seen as wheels
became worn so great attention was paid to maintenance
of running gear. Running maintenance requires frequent
and troublesome works, so research into preventing hunting
continued to enable future speed increases.
Running resistance of high–speed trains
Train resistance is a key factor in determining train performance. It includes running resistance, grade resistance, curve resistance, and acceleration resistance.
But the most fundamental is running resistance on straight,
flat lines. Running resistance is composed of mechanical
resistance and air resistance, so it is most affected by speed.
Air resistance (drag) in particular is nearly proportional to
the square of speed, so the value of running resistance at
high–speed operations is important in train performance.
However, running resistance at speeds above 200 km/h
was unknown territory at that time. Since train performance
cannot be designed when running resistance is unknown,
realistic estimates were needed. In 1958, the shinkansen
study group looked at RTRI running resistance tests using
train mock-ups, investigations by JNR rolling-stock designer
Shuichi Sawano (1918–) into SNCF’s 1955 test running
at 331 km/h using electric locomotives each hauling 3
carriages, and results from tests using Odakyu ElectricRailway’s Type SE EMU.
Qualitative trends were found from mock-up tests, but
there were no quantitative data, so tentative values were
fixed on estimation. Values deduced from running tests of
Series 80 EMUs between 1952 and 1956 were also used.
Based on these estimates and tests, the rated power of the
traction motors was decided, and test cars were built. By
luck and good judgment, the results from the test cars were
close to the formula estimates and a rough value of 10 kg/ton
was used when running at 200 km/h in the open (outside
tunnel). When the final trains were completed, the running
resistance was surveyed frequently to improve the accuracyof the formula, including running in tunnels.
Adhesion coefficient of high–speed trains
Adhesion is the fictional grip which transfers acceleration
or deceleration force between wheels and rails, and is
normally only about 30% in locomotives but is almost 100%
in gears. Consequently, adhesion is an important element in locomotive traction.
The planned shinkansen EMU consisted of powered
cars only with low acceleration and deceleration. As a result,
adhesion was not thought to be a problem, although the
adhesion coefficient when braking from high–speed was
unknown and caused some concern. It is one of the basic
factors for setting train deceleration and determining the
length of deceleration sections in the automatic train control
system. However, in the late 1950s, there was little reliable
information on the adhesion coefficient at high–speeds. The
RTRI could only find data from overseas for speeds at about
160 km/h, and there were only two or three examples of
guesses for the 200 km/h or greater range.
To solve the problem, the RTRI built a full-scale adhesion
tester in 1960. A pair of huge rotating wheels were used as a substitute for rails. The test data generally showed higher adhesion than actual rolling stock, so researchers believed it could not be applied to rolling stock design and train operation planning. Therefore, an adhesion coefficient (μ) of 13.6/(V+85) was adopted (where V is train speed) as the planned value for prototype shinkansen rolling stock; the
value was halved under wet conditions, taking into account
conventional test formulas and empirical data.
Although the ATC system was based on the adhesion
formula, the high risk of a disaster if the wheels do slide for
some reason resulted in the installation of skid detectors
on all axles. Contrary to expectations, the prototypes did
skid frequently on the test track in 1962, so the wheel skid
protection device was improved for the mass-production
cars, and tread cleaners were installed on every wheel.
Rust remained on the surface of rails at the start of
shinkansen operations, and skidding frequently occurred.
It took many years before most it was eliminated. Skidding
almost never occurred about ten years later.
Research on adhesion was actively carried out in
development of the next generation of rolling stock as frequent
sliding at the start of shinkansen operation unexpectedly
occurred. The biggest success was in quantifying to a certain extent the relationship between wheel and rail surface
roughness and adhesion coefficient. The wet state at each
wheel position of long trains was also identified. Those successes would be applied from the late 1980s.
|Photo: Adhesion Tester (RTRI)
High-capacity power supply
Long, high–speed trains need a reliable high-capacity power
supply—a problem that was easily solved by adopting the
increasingly popular AC electrification technology. The feed
voltage was set at 25 kV, which was the global standard at
that time. The early prewar plans for the bullet train called
for 3 kV DC, which was inadequate for longer, heavier trains,
making power collection difficult. A 3 kV DC system would
also suffer large voltage drop, requiring more substations at closer intervals. Italy runs high–speed trains at 3 kV DC but
is switching to AC and Russia has chosen AC for high–speed
lines rather than 3 kV DC.
Electric power for Tokaido Shinkansen is provided by local
power companies, using 50 Hz along approximately 180 km
from Tokyo, and 60 Hz for the remaining 370 km. Deliberation
was made as to whether cars should use both 50 Hz and 60
Hz or if power supply in the 50 Hz area should be converted
to 60 Hz. As using both would make the cars heavier and
cost more with the technology of the time, the whole line was
unified at 60 Hz taking future increase in the number of trains
into consideration. For that reason, frequency converters are
installed along the line at the Tokyo side.
Today, rolling stock that uses both 50 Hz and 60 Hz is
designed and produced for use on the Hokuriku Shinkansen. The Tokaido Shinkansen is still all 60 Hz.
Due to the high-voltage feed, the current is lower but even so a high–speed train can require collection of 1000 A. Images of the high–speed test of an electric locomotive in France in1955 showing large arcing between the overhead contact wire and pantograph suggested that high–speed current
collection would be a difficult problem.
Of course Japan at that time had no technology for
stable current collection at 200 km/h and the French high–speed
tests used a locomotive with only one pantograph,
but one would not be enough for shinkansen EMUs with
distributed traction. Vibration of a pantograph also affects
other pantographs when using multiple pantographs, making
technical issues even more difficult.
The basic conditions for stable current collection at high–speed
are ensuring that the catenary wave propagation
velocity is faster than the train velocity as well as having a uniform pantograph uplift spring constant.
However, according to theory of the 1960s considering
a mid- to high–speed range up to 200 km/h, speed with no
contact loss is, from a pantograph standpoint, found by the
up-down movement vibration theory with the contact wire
resembling the strings on a stringed instrument. Thinking of
the contact wire as springs lined up perpendicularly, speed
with no contact loss is found and calculated from uplift
characteristics by the pantograph.
As a result, wire contact at faster speeds could be assured by:
• Decreasing the mass of the pantograph, especially
• Increasing the contact wire tension, and making the
• Minimizing the irregularity of spring constant.
This theory dominated until the early 1980s and catenary
wave propagation velocity was not thought to be a problem
at the predominant operating speeds of that time.
The RTRI started full-scale research in 1955 to develop
a high-speed current collection system. The first tests were
run on the Tokaido main line for the speeds of 95 to 120
km/h, but research started from the end of 1957 on what was at the time super high-speed current collection for the
shinkansen speeds of 200 to 250 km/h.
Keeping the catenary spring constant fixed is
impossible, because the overhead line is supported by
poles. However, to keep it as fixed as possible, comparative
tests were run on anti-resonance, modified Y-shaped
compound catenary, continuous mesh catenary, and
composite catenary on the Tohoku and Tokaido main lines.
To decrease pantograph mass, overhead contact line height
was made constant and pantograph vertical motion was
decreased. They thus became smaller and lighter. To make
the mass of the collector head in particular smaller, one
pantograph was provided for two motor cars and the power
collection current was reduced. A 16-car train set would
thus have eight pantographs.
Anti-resonance catenary, modified Y-shaped compound
catenary, continuous mesh catenary had complex
structures, and maintenance was difficult, so composite type compound catenary system was chosen. In this method, the contact wire is slung from dampers which absorb wire vibrations from the pantograph, making it ideal for the multi–pantograph shinkansen EMUs. This was the system devised by the RTRI.
The initial performance of the composite type compound
catenary was very good, but increasing numbers of
train operations caused wear at the contact wire and
deteriorated dampers, leading to many wire breaks.
Although contradictory to current collection theory, the
countermeasure was to strengthen the pantographs. And
from the 1970s, dampers were eliminated and thicker contact
wires were used. This heavy compound catenary had fewer
wire breaks, but more loss of contact and resultant arcing
caused more noise along the line. Such contact loss did
not affect AC-based train operations research continued to
eliminate contact loss with major later successes.
In pantograph design, the issues facing making them
smaller so they are lighter were overcome by fixing overhead
contact line height. However, such pantograph design faced issues with wind-generated irregular lift. Wind against
pantographs when running is strong, and lift acted up and
down irregularly on the collector head and disrupted the
contact force on the contact wire. Wind-tunnel tests led to
collectors of various shapes offering slight positive lift to
increase contact force and each new pantograph design is now subjected to wind-tunnel tests to confirm lift forces.
|Figure 3: Overhead Catenary Structure
Figure 4: Pantograph Comparison
Photo: Silicon Rectifier for EMUs (100 Years of JNR Rolling Stock)
The traction system where the train collects high-voltage AC
power to turn the traction motors was made to be a power
distributed EMU system in line with Hideo Shima’s ideas,
which was accepted unanimously. It was designed to lighten
axle loads and solve adhesion problems and it also offered
stable electrical braking and lowered brake maintenance.
High-speed EMUs designed under that idea were not
seen anywhere else in the world back then. At that time,
European high-speed trains running in the 160 km/h range were mostly loco-hauled but after the
appearance of the 200 km/h shinkansen,
some European operators increased
operating speeds to 200 km/h and more,
and soon realized the need for lighter axle
loads as roadbeds became damaged.
AC traction systems at that time were
either direct types using AC commutation
motors (mainly low frequency, such as 16.7
Hz) or indirect types with rectifiers and DC
motors. The latter had an advantage for AC
electrification using commercial frequencies
but the large mercury rectifiers used then
could not be mounted easily under the floor of EMUs.
As a result, efforts were made to develop a system using commercial frequency AC-commutator motors with regenerative braking, but that proved extremely difficult.
As JNR designers and electronics manufacturers agonized
over the development, silicon diodes for electric power
semiconductors appeared. Although many elements had to
be connected in series and parallel, under-floor mounting
became possible and they were put to practical use on dual AC-DC EMUs running on conventional lines in 1960.
Shinkansen EMUs were soon equipped with semiconductor
rectifiers for a system with DC main motors. It proved
incredibly reliable and was used for more than 20 years.
Large volumes of the new electric power semiconductors
could be stably supplied thanks to the development cooperation of Japanese electric manufacturers.
Passenger cabin air pressure
As tests of prototype shinkansen rolling proceeded at faster
speeds, the problem of in-cabin air pressure emerged.
Air pressure changes greatly as a train enters a tunnel
at high-speed, creating an unpleasant popping feeling
in passengers’ ears. The phenomenon had been seen
previously in the single-track tunnels, but its occurrence in
double-track tunnels was unexpected.
Although popping ears is not a major problem for
healthy people, it can be painful for people with colds, etc.,
so a decision was taken to make the car body airtight. The structure of bodies is complex, and a fundamental change in terms of design and production technology was needed.
Cars that were strong enough to withstand external air
pressure changes were needed, but time was short. For
early production cars, areas centring on the passenger
cabin were made airtight and ventilation ducts were closed
when tunnels were detected to secure cabin ventilation.
But making the passenger cabin airtight caused problems such as poor opening and closing of doors and backflows
in places using water such as the toilets and buffets.
Overcoming these problems became a major task. In the
end, the whole car body was made airtight. Outside doors
were sealed by air pressure; airtight diaphragms were
developed for couplings between cars; and waste water for
washrooms and buffets water is passed through a seal (U–shaped
pipe holding water at a height of 300 mm or higher)
to prevent air flow between the inside and outside.
And because air starts leaking with aging wear, criteria
were established for checking air-tightness regularly at maintenance shops to keep it at a certain level.
Continued to JRTR 58.
|Figure 5: Example Air Pressure Fluctuation Over Time (Lead Car)