Traffic spike

InakaYabanjin has thoughtfully warned me to watch out for a hazard plaguing Japan's motorways: jagged metal shards affixed to the roadside guardrails. Kyodo News reports:

Sharp-edged pieces of metal, some of which were protruding and have caused injury to people, have been found on road guardrails in all of Japan's 47 prefectures, prefectural and central government officials said Friday.

Following earlier reports by Saitama and Nagasaki prefectures, Aichi, Chiba and Tokushima prefectures reported Friday that residents had been injured by protruding metal while cycling or walking along the road.

These metal shards look pretty fearsome, as the following photo from the Mainichi Shimbun suggests:So where are the shards coming from? One theory, put forth by the Ministry of Transportation, holds that they're left behind by cars scraping the guardrails. Kyodo reports:

The ministry said it now believes that vehicle collisions are a possible source of the metal as one of the pieces examined in Aichi Prefecture was made of steel used in auto manufacturing.

But it seems unlikely to me that a piece of metal would rip off the side of a car and wedge itself right between the rail panels as seen in the above photo. And it seems even less likely that it would happen in some 21,000 locations across the country, according to another Kyodo News report. In fact, in that later report, officials admit bad driving can't explain all the shards:

Vice Minister of Land, Infrastructure and Transport Satoshi Iwamura told reporters that the metal pieces cannot only be explained as being left over from vehicle crashes.

Other people suspect the shards were deliberately put in position as a form of low-grade domestic terrorism. The Mainichi reports:

Akira Sakuta, a criminal psychology expert and lecturer at Seigakuin University, said a group of people might have been involved.

"I suspect that those who want to injure people and cause trouble have inserted the objects," Sakuta said.

But again, the wide geographical range and large number of shards means it would have taken a large, determined, and well-coordinated group to plant them in so many places. And, according to the Mainichi, only four people have been injured by the shards so far. It seems like such a plot would require an incredible amount of work for negligible results.

The real answer seems to have been uncovered by oyajikun, a commenter on the JapanToday discussion boards. He writes:

They are nothing more than the remnants of the flag pole type signs you see along most roads advertising pachinko, kabakura [cabaret clubs] and delivery health.

He helpfully provides a link to photos and a diagram of such sign flagpoles and how they are installed:It seems like this case could be closed. And some safer signpost attachments are in order.