Failure Knowledge Database / 100 Selected Cases

Amarube Railway Bridge Accident
December 28, 1986 at the Amarube Railway Bridge on the Sanin Main Line in Amarube, Kasumi,Kinosaki, Hyogo
Masayuki Nakao (Institute of Engineering Innovation, School of Engineering, The University of Tokyo)
An outbound tr ain was traveling from Fukuchiyama to Hamasaka on the Sanin Main Lin e when a strong gustof wind blew it off the Amarube Railway bridge. The maximum wind velocity was 33 m/s at the time. Sev enpassenger car s f ell ap proximately 41m on a s eafood pr ocessing factory and residences. The accident kill ed 1
train operator and 5 f emale factory workers, and injured 6 people. The c onductors did not stop the traffic eventhough they knew th at they s hould h ave av oided cr ossing the bridge du ring strong winds. Photo 1 is a press
photo of the accident.

Photo 1. Train was blown off the Amarube railway bridge and caught fire [1]1. Event1

Failure Knowledge Database / 100 Selected Cases
An outbound train was traveling from Fukuchiyama to Hamasaka on the Sanin Main Line when a strong
gust of wind blew it off the Amarube Railway bridge. The maximum wind velocity was 33 m/s at the time.
Seven passenger cars fell approximately 41m on a seafood processing factory and residences. The accident
killed 1 train operator and 5 female factory workers, and injured 6 people.
2. Course
When 1986 was about to end on D ecember 28, the 7-car special train “Miyabi” with sunken kotatsu seats
and k araoke was car rying tourists on the “Sanin Sh opping Tour” from th e T anigawa S tation o n th e
Fukuchiyama line. A fter un loading 176 passengers carry ing lo ts of s eafood products for the N ew Year’sHolidays at t he Kasu mi S tation, the tr ain was tr aveling wi thout pass engers nea r t he Amarube Railwa ybridge towards Hamamatsu on the outbound line.
The sa fety re gulation specified shutdown of the Amarube Rai lway bridge d uring stron g winds wh en th emaximum w ind velocity was 25 m/s or greater. The r ailway b ridge ha d au tomatic wind vel ocity senso rs(anemometers) on b oth s ides around th e cen ter. W hen t he win d v elocity exceeds t he safety li mit, t heCentralized Train Control (CTC) at the Fukuchiyama Railway Bureau warns conductors with a red flashinglight and a wailin g alarm . Th e conducto rs thenmust r emotely activ ate t he light signal (apentagonally-shaped signal with 5 red light bulbs that flashes in sequence) to inform danger and stop trains.
The Amarube Station located west of the railway bridge was an un manned station at that time after CTC
installation.
At around 13:10, the CTC alarm went off warning a strong wind over the maximum wind velocity of 25m/s. The control center, which did not have information on the exact wind velocity, contacted the Kasumi
Station an d f ound that the wi nd velo city was about 20 m/s, less th an the s afety l imit. Knowing that notraffic was scheduled to cr oss the railway bridge at that particular time, the control center decided to takeno action.
At 13:25, the CTC alarm went off again. The control center contacted the Kasumi Station and found thatthe maximum in stantaneous wind v elocity h ad reached 25 m/s an d it was th en 20 m/s . The t rain hadalready pass ed th e Yoroi S tation 2 minutes earlier a nd was entering th e Ama rube R ailway br idge. The
conductors assessed the situation and concluded that it was too late to activate the manual control lever tostop the train. The manual control lever was not activated.
Different ac counts report that the co nductors wer e t oo busy handling another train’s fa ilure to s trop
crossing the bridge crossings.
After checking the unlit light signal located west of the railway bridge, the operator drove the train to crossthe railway brid ge. The o perator r educed the travel sp eed f rom 6 0 km/h ( default) to 48 km/h d ue t o thestrong wind. In the middle of the railway bridge, the train was hit by a gust of wind of 33 m/s. It was the4th strongest wi nd on record during that wi nter. The middl e cars started fallin g on the south side of therailway bridge ( the en d car s with power supply weigh ed more), pulled the rest of the railcar s except theengine. I ts h eavy wei ght sa ved the engine. The weight of th e f alling c ars tor e th e br ake p ipe, causi ng
2Failure Knowledge Database / 100 Selected Cases
automatic brakes to en gage ( failsafe sy stem). Th e train op erator on th e engine looked b ack to check therear and found no passenger car.
The Amarube Railway bridge was brought back in service 3 days after the accident, at 15:11 on December
31.
3. Cause
The pr incipal fac tor r esponsible for th e accident was the c onductors’ la ck of s afety cons ciousness. T heconductors sh ould have s topped th e train without cr ossing the bridge wh en the CTC alar m went off.
Ignoring the safety regulation, the conductors took no action to stop the tr affic. It was later revealed thatthey had the customary practice of c ontacting the Ka sumi S tation upon no ticing th e al arm. T his wasprobably becau se the one of the s ensors was not fun ctioning and the other one g ave in accurately lo wer
readings. Th is practice caused delay in sto pping the train while the co nductors we re co ntacting Kasumi
Station.
4. Immediate Action
Amarube Accident Technical Inv estigation Comm ission was es tablished after the acciden t to i nvestigate
the c ause o f the a ccident. T he i nvestigators per formed w ind tunnel tests to obtain th e threshold wi ndvelocity at which railcars overturn in normal train operation. The results showed that railcars are likely tooverturn at 33 m/s of wind velocity (Amarube Accidents Investigation Report).
5. Countermeasure(1) The warning light signal was direct ly co nnected to t he wi nd v elocity sensors t o auto mate t he a lert
tripping. Human operation was eliminated as shown in Figure 1.
(2) The wind velocity to stop the train operation was set lower to 20 m/s from the previous 25 m/s.
(3) W indscreens were installed to the railway bridge.

Figure 1. Control Loop of Safety System [1]6. Summary
Even though the wind velocity sensors (automatic wind velocity sensors) had sent a warn ing to the CTC
center, the conductors did not immediately stop the bridge crossings. The conductors delayed activating the3Failure Knowledge Database / 100 Selected Cases
manual lever to confirm the actual wind velocity at that time. Because of the conductors’ poor judgment,
the train fel l off the railway bridge. Human role in the control-loop of the safety system contributed to t heaccident. Human operators m ay ignore war ning signals. Head- on collis ion will occ ur, if train operators
ignored a red signal on a single-track line.
It was f ortunate th at the train was n ot in ser vice at that t ime a fter unlo ading a ll 176 passengers at theKasumi S tation. The cond uctors may hav e taken str icter saf ety prec autions if t he train was carrying
passengers, but their lack of safety consciousness would have caused an accident sooner or later.
7. Knowledge(1) The control-loop of safety system should not include human interaction.
(2) Even though sensors of safety systems trip alarms, human operators may ignore them if th ey believethat the sensors are not accurate.
(3) Human o perators te nd to f ollow ge nerally accepted practice r ather tha n rigorous sta ndards. It i sessential for operators to fully understand the reason why they have regulations and manuals to follow.
8. Background
The Amarube Railway bridge opened in 1912 (Meiji 45) after 2 years of construction by 250,000 workers
with 330,000 yen of buildin g expens e. Seiichi Furukaw a, an e ngineer of the Min istry of Ra il Road, andothers with a dvices from American engineers designed the steel trestle bridge (trestle means “mounting”).
The trestle material (bridge support) was shipped from the U.S. and barged to the Amarube shore. It was
the most dif ficult construction on the Sani n Main Line. The S anin Main L ine op ened after the r ailwaybridge was co mpleted. The 41m-high and 310m-long railway bridge was the biggest bridge in A sia at thetime. It is still the biggest trestle in Japan (Excerpt from the guide plate of the Amarube Railway bridge).
The trestle consists of a number of short spans, supported by vertical steel beams. It is surrounded on threesides b y steep mountains, f acing th e Sea o f Japan at its n orth. The site is often h it by sno wstorms andsevere winter gales. Locate d 70m fr om the co astline, t he bridge required f requent ru st p roofing an dreplacement of r usted e lements. S hortage in ma intenance supp lies during and after the wa r seve rely
deteriorated the structure and eventually a 5-year repair plan was carried out from 1956 to 1 963. A 8-year
maintenance plan in 1968 also r eplaced all spans to reinforce the railway bridge. In 1976, 64 years afterconstruction, the trestle was reborn as a concrete bridge.
Some argues that the accident was not caused by a strong gust of wind, but by self-excited oscillation, likein the case of Tacoma Narrows Bridge accident, induced by imbalance in the repaired bridge columns (onlyhorizontal el ements wer e r eplaced). The tr ain derailed traveling on th e track warped by self-excitedoscillation (Photo 2).

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Failure Knowledge Database / 100 Selected Cases

Photo 2. Warped Track (Wind blew from the ocean on right to the mountains on left) (Jiji Press Co.) [1]
The accident took place before the demise and privatization of JNR (April 1, 1987) and the operators tried
not t o st op the traffic u nless it was absolutely necessary bec ause suspending t he train ser vice may affecttheir reemployment.
The n ew safety regu lation that s pecifies no bridge cr ossing at 20 m/ s of wind vel ocity results in m any
delays and suspensions during the winter when crabs are in season. The r ailways are currently discussing
plans to improve the service. The Amarube railway bridge has an incomparable historic value that makes agood local r esource for touris m. I n ord er to provi de on-time s ervices and landscape impr ovement, th erailway is considering installing a prestressed concrete (PC) rigid-frame (Rahmen) pier. A PC rigid-frame
bridge uses reinforced prestressed concrete. Its frame structure has columns and beams rigidly connected at
joints to pr oduce extra strength against loa d. The joint structure is tough against deter ioration and decay.
(New Bridge Investigation Commission, chairman: Masaru Matsumoto, Professor, Kyoto University)
9. On the Side
Operators who ha ndle a faulty system wind up crying wolf so many times. They will then disbelieve thesystem an d star t fo llowing an acceptable practice that co mpensates th e unrel iability of the faulty system.
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Failure Knowledge Database / 100 Selected Cases
As seen in this accident, such a practice of contacting the station aggravates the risk of accidents.
References[1] Yotaro Hat amura (Edit or), Jissai-no Sekkei (Practical Design) Res earch Foundat ion (1996) Zoku-Zoku
Jissai-no Sekkei (Practical Design III), The Nikkan Kogyo Shimbun, LTD.
[2] Yasutomi Sasaki, Ryoichi Amiya (1995) Zoku Jiko-no Tetsudooshi (History of Train Accidents II), Nihon
Keizai Hyoron, LTD.
[3] “Web News: Teiji Unkoo Kakuho-to Keikan-no Ryooritu-o, Amanobe Tekkyo Kakekae Keikaku (On-TimeServices and Lan dscape Improvement, Reinforcement Plan of Amarube Rai lway bridge)”, The Kobe
Shimbun, September 6, 2003, http:// www.kobe-np.co.jp/6