Failure Knowledge Database / 100 Selected Cases

Hibiya Line Derailment Accident
March 8, 2000 at Naka-Meguro on the Teito Rapid Transit Authority's (TRTA) Hibiya line
Masayuki Nakao (Institute of Engineering Innovation, School of Engineering, The University of Tokyo)
1. Event
Near the Nak a-Meguro Station on the TRTA’s Hibiya line in Tokyo, the l ast car of an 8-car subway train
bound for Kikuna from Kitasenju derailed on a curve. The 5th and 6th cars of oncoming 8-car train boundfor Takenotsuka from Naka-Meguro hit the derailed car. The Hibiya line had 3.5m of track-center distance
between the inbound and the outbound tracks. The accident claimed 5 lives and 63 injuries.
2. Course
At around 9:00 am on March 8, 2000, the 8-car subway train A861S bound for Kikuna from Kitasenju wascarrying approximately 10 0 pa ssengers on it s way t o the Naka-Meg uro Station o n the T RTA’s outboundHibiya line (A line) in Tokyo.
At 9:01 am, two wheels of the last car (carrying 6 passengers) of the subway train detailed 150m before theNaka-Meguro S tation when itwas traveling at ap proximately 12 – 13km/h on a s loped ( 35/1,000)

transition curve (between curve and straight lines) following a left curve of radius 160m. The derailed train
stopped on the railway sleepers at the br anching of t he setoff equipment (for bringing a maintenance train
to the main line) lo cated 50 m away from the derailed point. The derailed train was h it by the onco ming
Tobu Railway’s 8- car train B8 01T b ound fo r Takenotsuka from Naka-Meguro car rying 1, 000 p assenger,
which was traveling on the inbound line (B line) that had a 3.5m track-cen ter distance from the outboundline (A line).
The collision badly damaged the 8th car of the A861S as well as the 5th and the 6th cars (each carrying 125passengers) of the B801T.
Figure 1 illustrates details of the accident.

1. The 8th car of the A861S derailed.
1Failure Knowledge Database / 100 Selected Cases

2. The B801T collided with the A861S.

3. The B801T and the A861S stopped.
Figure 1. Schematic Illustration of Accident Site [1]The accident killed 5 and injured 63 people.
After the collision, the A861S operators activated the emergency brake and stopped the train. The B801T
stopped travelin g as th e emer gency br ake was automati cally ac tivated in respons e to th e rupture of th e
brake pipe located between the 5th and the 6th cars.
The 8 th ca r of the A861 S h ad its right side in t he traveling direction dam aged severely from it s front
towards the center door a rea. The 5th car of the B801T had its right front area damaged and its right side
heavily scratched in the center door area towards the end of the car. The 6th car of the B801T had its rightside damaged severely from its front towards the first door area. The collision also left scratch marks in therear area of the 4th car, the center area of the 7th car and the right side of the 8th car. The electric cable andthe brake pipe were also damaged on the right side at the connection between the 5th and the 6th cars.
The outer track on the curve where the wheels derailed had 7m-long skid marks made by the flange startingat the 18.333 km point and shorter marks at th e 1m-point from where the wheels derailed. The inner t rack2

Failure Knowledge Database / 100 Selected Caseson the curve also had small marks.
The outer wheel tread and the flange had marks shown in Figure 1 within the 1.3m-radius of the first axle.

Figure 2. Derailment Marks [1] (Modified)
3. Cause
The derailment occurred at the entrance to a transition curve following a sharp left curve, where moderatetorsion of the track surface (within the limits allowed by the s afety standard) causes weight imbalance inthe train wheels on both sides (weight decrease in the right wheels and lateral force increase, see Figure 3a).
It is believed that this and other factors increased the derailment coefficient in the right wheel of the 8th
car’s f irst axle, ca using the whe els to r un ov er the track b efore actual ly ju mping the track (Figur e 3b).
Derailment of this sort is called the “run-over-the-track” derailment.
The i nvestigation made t he following discoveries a nd concluded t hat we ight imbalance in the f irst-axle
train wheels contributed to the derailment:(1) The pr oduction measurement sh owed t he f irst-axle and th e four th-axle train wh eels su pported lessweight of the train. The weight of the train was not distributed evenly.
(2) The railways did not perform maintenance of weight balance after the railcar was put in service.
(3) Other railcars of the same model (Model 03) showed the same weight imbalance in the train wheels.
In ad dition t o the ex isting weight imbalance i n the m odel, t he f ollowing factors worsened th e we ight
imbalance in the tr ain wheels (weight decrease in the right wheels and lateral force increase). The current
design an d maintenance d o not co nsider so me o f th em to be d efects, and so me pose difficulty in proper
maintenance. These factors may or may not contribute to train derailment.
• The coefficient of friction between wheels and th e track increased when the train traveled on the curve,
and this increase resulted in an increase of lateral force.
• The characteristics of the axle spring and the stiffness of the air suspension that damps out the motions of
the railcar contributed to an increase in lateral force and a decrease in weight in the right wheels.
3

Failure Knowledge Database / 100 Selected Cases• Lateral force increased because of the shape of the wheel tread in co ntact with the particular surface ofthe track that was shaved to remove scratches and dents.

Figure 3. “Ran-Over-the-Track” Derailment
4. Immediate Action
On March 8 , the day when the acci dent hap pened, the A ccident I nvestigation Comm ission (C hairman:
Masakazu Iguchi, Professor, Emeritus at the University of Tokyo) submitted the investigation report to theTransport Ministry of Japan at its first meeting. Th e commission agreed on establishing a working group
and necessary measures to be taken before reopening the service:(1) All railcars of the accident model must have a complete overhaul on its air suspension and bogie.
(2) A der ailment prevention gu ard (r ail or a ngle st eel ins talled o n th e inner si de of a t rack to preventderailment) must be installed at the derailment point.
(3) The travel speed must be reduced to 15 km/h or less near the derailment point.
At the second meeting held on March 16, the following measures were imposed on all railways includingtransit authorities that provide passenger services to prevent similar accidents from happening.
For all curves of 200m radius or less:(1) A transition c urve that foll ows a cur ve mus t hav e a derailment prevention guard, a derailment
prevention rail or a safety rail installed.
4

Failure Knowledge Database / 100 Selected Cases(2) For other sections, a derailment prevention guard, a derailment prevention rail or a safety rail must beinstalled. The installation will start from sections that have higher risk of derailment after assessing theconditions including the gradient ratio and radius of curvature.
The Transport Ministry ordered the installation to applicable railways.
5. Countermeasure
On October 30, the TRTA announced the derailment prevention measures in response to the advisory report
given by the Accidents Inves tigation Commission of th e T ransport Ministry. T he TR TA compl etedadjusting the wheel weig ht rati o (indicatin g the balance of w eight in the t rain w heels on both sides) t owithin 15% o r less for all Model -03 railcars allocated to the H ibiya lin e by June and for 90 % of all
Model-03 railcars on all lines by October 10. In 2001 the TRTA set the stricter guidelines and adjusted thewheel weight r atio to be 10% o r less. It als o installed 5 new co ntrol sy stems (40 – 50 m illion yen per asystem).
The f langes were angles were s et to 60 d egrees f or all r ailcars in ser vice o n th e Hibiy a, C hiyoda and
Yuraku-cho lines at the time of the accident, and TRTA changed this angle to 70 degrees for railcars on theHibiya line by No vember 9, Chiyoda and Yuraku-cho lines by Se ptember 2001. The railcars in service onother lines originally had flanges angles of 67- 70 degrees.
The TRTA’s per iodic shavi ng operation will r emove scr atches and d ents t o maintain the original surface
and shape of track on sharp curves. The T RTA Railway commissioned the Technical Research Institute todetermine the optimal track shape.
The TRTA lengthened the transition curve at the derailment site by 10m from 30m to 40m.
6. Summary
The Acci dent I nvestigation Co mmission cond ucted the acciden t i nvestigation i ncluding f ield stu dy andanalysis from the day when the accident happened until October 26 of the same year. In order to determine
the direct cause of th e derailment, the investigators recreated the accident as accurately as possible at t heaccident site and examined the railcar’s motion. The investigators also ran a simulation to a nalyze various
factors and determine the extent of their contributions to the derailment.
The C ommission est imated th e safety factor ba sed on the derailment c oefficient ca lculated by using theformula: Estimated ratio o f derailmen t coefficient = De railment coefficient l imit / Esti mated for mula ofwheel w eight and lateral force. Es timated r atio of derailment coefficient repres ents the rati o between t he
maximum lateral force and the minimum wheel w eight. The in vestigators ana lyzed r ailcars’ moti on on
curve as well as various factors that influence wheel weight and lateral force to obtain the safety factor.
In light o f th is trag ic accident, t he Acciden t I nvestigation Commission a nnounced the follo wingrecommendations at its fifth meeting held on July 31, 2001.
(1) To f acilitate quick investigati on upon an accide nt, accumulation of accident-related kno w-how anddata, and continuity of accident investigation, it is necessary to estab lish a permanent and specialized5

Failure Knowledge Database / 100 Selected Cases
investigation syst em that can conduct specialized accident investigations along with a system toprevent recurrence of ac cidents due t o si milar c auses. (This gave concr ete impetus for of ficial
establishment o f the Aircraft and Railway Ac cident In vestigation Com mission, an indepen dent
standing commission of the Ministry of Land.)(2) To assure smooth investigations of accidents, the Commission must collect and hold accident-related
data and it ems. ( The com mission investigators ar rived at the a ccident si te af ter the p olice collected
evidences, which had been always the case in accident investigation. When an accident happens, theinvestigation of criminal negli gence is g iven p riority over inves tigation of a ccident ca uses in J apan,
which m akes it di fficult for the investigation com mission t o determine t he direct ca uses a nd help
preventing recurrence of accidents. In this accident, the commission investigators were able to o btain
the evidences because they were also crime laboratory officers of the police. )(3) Fundamental R&D into railway accidents must be promoted.
7. Knowledge
A combination of various fa ctors may cau se an acc ident. I n orde r to de termine the actual cau se of eachaccident, i t is esse ntial to comprehensively study e very factor t hat may have c aused t he accident andestimate th e safety fac tor. Before preventing recurrence of ac cidents, in vestigators mus t und erstandcircumstances and the ser ies of event s that led to th e ac cident. Not e th at t he s afety fact or a ccount forimperfections i n mater ial, flaws in ass embly, material degradation, a nd unce rtainty i n loa d estimates.
Periodical maintenance must pr event c hanges in s hape, which occurs due to we ar, because su ch changes
lower the safety factor.
8. Background
Before this Hibiya line accident, the railways had been testing the railcars for their wheel weight and lateralforce whenever some change, such as new models, new lines and an increase in travel speed on a line, ismade to the service to e nsure safety. Such a test was conducted on the first axle under the exp ected travel
speed. However, the field study of th e accident found th at th e derailment coefficient is greater in wheelsthat have smaller weight ratio when the railcar travels slowly on a transition curve following a sharp curve.
The accident proved the need for testing all axles.
For the wheel weight imbalance, which was another cause of the accident, the railways’ production process
did not include testing and adjustment of wheel weight balance at factories. (In response to the advisory by
the investigation co mmission, al l r ailways s tarted t esting wh eel w eight for all wheels and axl es wi thin 2
years from the accident.)
References[1] Railway Acc idents Inves tigation Co mmission ( 2000) Derailment at the Teito Rapid Transit Authority’sNaka-Meguro Station on the Hibiya Line, Japan, October 26, 2000, The Ministry of Transport of Japan.
6Failure Knowledge Database / 100 Selected Cases[2] NEW S FILE (Railway Topics), Tetsudo Journal (Railway Journal), February 2002,
http://www.railfan.ne.jp/rj/main/news_102x.html

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