Information on the accident is dribbling out via the media, not directly through the tunnel operator NEXCO Central, whose website has zero information on the accident other than their "Sorry for the accident victims" message, or the ministry in charge (Ministry of Land, Infrastructure, Transport and Tourism) which set up an investigation committee made up of scholars and university professors (as if they had ever worked a day in construction).
First, from Yomiuri Shinbun (12/4/2012):
The Investigation committee of the Ministry of Land, Infrastructure, Transport and Tourism surveyed the accident location and met for the first time on December 4 after the Sasago Tunnel accident in Yamanashi Prefecture where the ceiling panels collapsed [killing 9 people].
The committee revealed to the press that there was no noticeable corrosion on the anchor bolts that fell from the ceiling. The committee will further investigate in order to determine why the bolts fell.
The survey lasted for about one hour. The committee members saw the anchor bolts that fell, and looked at the concrete ceiling of the tunnel. According to the committee, there was no evidence of large flaking of concrete, and while some anchor bolts showed some rusting, it was minor.
The committee also confirmed the maintenance method with the Central Nippon Expressway Company. According to the committee, they were "conducting the maintenance according to the internal manual, but we cannot determine at this point whether the manual was appropriate."
As if there is only one manual. From my personal experience, they may have at least three manuals, one for the submission to the regulatory authority, one as the official company manual, one as the unofficial manual for the field workers. I wouldn't be surprised if there's yet another one, unofficial, oral manual handed down the workers who really know the situation.
However, NHK, reporting on the police investigation, says bolts were corroded and cracked (12/5/2012; part):
According to the police investigating the scene, there were multiple metal bolts that had fallen from the tunnel ceiling, which had been used to secure the metal bars that had suspended the ceiling panels.
Some corrosion was found on the bolts, and some of them were found cracked, according to the police. They will further investigate how the bolts fell.
Does the Ministry of Land, Infrastructure, Transport and Tourism have the minutes of the expert committee meeting on December 4? Yes it does, sort of. The ministry's website has a "minute summary" that consists of seven short sentences. As to the accident, it has this to say:
2) How the accident happened
- There was a discussion of how the accident happened.
You would think the government and the government experts have learned the lesson from the Fukushima accident - that information needs to be promptly and fully disclosed. So we have no choice but rely on the media, and muddle through.
Life is completely back to normal in Japan.