JAPAN HAS ordered emergency inspections of its entire rail tunnel network after a 200kg tunnel lining section crashed onto the roof of a speeding bullet train.
More than 4,500 tunnels covering Shinkansen (bullet) train, suburban and underground lines, are involved. Their total length is 3,360 km.
The checks have been ordered by the Japanese transport ministry which has given Japan Railways until the end of this month to comply.
Initial surveys on the Sanyo Shinkansen line, where the accident occurred last month, have already found structural defects at more than 2,000 locations with 97% - 1,988 - in 84 tunnels between Okayama and Hakata stations.
The Sanyo Shinkansen line is operated by West Japan Railway Co (JR West) which said the lining problems resulted from cold jointing, where concrete was allowed to harden with little preparation before the next layer was applied.
Industry sources said poor quality cement may have also been used to save money during tunnel construction which coincided with Japan's first oil crisis in 1974.
The Okayama-Hakata section was inaugurated in March 1975.
JR West has nearly completed inspections on 147 tunnels on the line between Shin-Osaka and Hakata.
A JR West spokesman said the incident was 'an accident of unprecedented seriousness'. The concrete slab ripped open a 12m long section of the train's roof and damaged the pantographs on two rail cars as the train passed through Fukuoka tunnel in Hisayama, Fukuoka Prefecture, at nearly 220km/h.
None of the 350 passengers on board was hurt, but the train was halted for about 90 minutes. The incident also led to 14 trains being cancelled.
Similar inspections are being carried out by East Japan Railway Co (JR East) which is examining all 162 tunnels on its Tohoku, Joetsu and Nagano Shinkansen lines.
JR East has drafted in about 100 track maintenance workers to carry out the inspections which are being undertaken visually during two night time possessions between 1.30am and 3.30am.
Central Japan Railway Co (JR Tokai) has also begun checking 66 tunnels on its Tokaido Shinkansen line between Tokyo and Shin-Osaka.