Nine people were killed Sunday in the tunnel, a major link between the capital and central Japan that opened in 1977 at the peak of the country's postwar road construction boom. Police searched the tunnel operator's offices Tuesday, looking for evidence of negligence.
The transport ministry has ordered inspections of 49 other highway and road tunnels of similar construction around the mountainous country.
Much more of Japan's transportation system may require refurbishing after years of spending cuts that starved projects of funding, including for needed basic maintenance.
The infrastructure ministry, which is in charge of land and roads, joined with three government highway operators last month in forming a panel on how to handle problems of deteriorating expressways and tunnels.
Experts told the panel that about 40 percent of the 8,716 kilometers of expressways the agencies run had been in operation for more than 30 years, the Yomiuri newspaper reported Tuesday.
The paper cited Kyoto University expert Toyoaki Miyagawa as saying that countermeasures are "urgently needed" because the roadways and tunnels were built according to specifications suiting much lighter traffic loads than today's.
Such projects would pose an extra burden at a time when Japan's public debt already has soared to more than 200 percent of its GDP.
Miyagawa said Sunday's tunnel accident likely resulted from a faster-than-anticipated aging of the structure.
About 270 concrete slabs collapsed onto the roadway deep inside the Sasago Tunnel 80 kilometers (50 miles) west of Tokyo, falling on three moving vehicles.
Central Nippon Expressway Co., the tunnel's government-owned operator, said it had no record of any major repairs performed since the tunnel opened, but company official Satoshi Noguchi said an inspection of the tunnel's roof in September found nothing amiss.
About a dozen uniformed police were shown on television Tuesday entering the company's headquarters in the central city of Nagoya, toting cardboard and plastic boxes.
"Yes they are searching our offices here. We will be fully cooperating with them," said Osamu Funahashi, another company official.
The slabs, each weighing 1.4 metric tons (1.54 short tons), fell over a stretch of about 110 meters (120 yards). They had been suspended from the arched roof of the tunnel.
The operator was exploring the possibility that bolts holding a metal piece suspending the panels above the road had weakened with age. The panels, measuring about 5 meters (16 feet) by 1.2 meters (4 feet), and 8 centimeters (3 inches) thick, were installed when the 4.7-kilometer-long (3-mile-long) tunnel was built.
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Recovery work in the tunnel about 80 kilometers (50 miles) west of Tokyo halted Monday to allow reinforcement of the roof to prevent more collapses, said Jun Goto, an official at the Fire and Disaster Management Agency.
By Tuesday, crews were removing the concrete slabs from the tunnel, said Goto, who added that authorities do not expect to find any more victims inside.
Spending on public works once was the lifeblood of the conservative Liberal Democratic Party, which has ruled Japan for most of the decades since in World War II, though it was ousted by the Democratic Party of Japan in 2009.
The government created huge oceanside reclamation projects, bullet train lines and other vital infrastructure, as well as notorious "bridges to nowhere."
Political reforms beginning in the early 2000s focused on cutting spending on public works, but they failed to differentiate between projects that contributed to efficiency and competitiveness and those that did not, said Masahiro Matsumura, a politics professor at St. Andrews University in Osaka, Japan.
"Basically, we didn't spend enough on renovating our decaying water pipes, bridges and tunnels. We didn't spend enough on public infrastructure," Matsumura said.
Japan, however, has other expensive needs, even as it tries to cope with massive debt. Rebuilding from the March 2011 earthquake and tsunami, and ensuing nuclear disaster, is diverting attention and resources from such wider issues.
LDP chief Shinzo Abe has made boosting public spending a key platform of his campaign in the Dec. 16 parliamentary election. He accuses current Prime Minister Yoshihiko Noda of not doing enough to stimulate the economy after two decades of stagnation.
But what worked decades ago during an era of fast growth and ample tax revenues may not have the same impact in today's fast-aging Japan, especially when the economy is suffering from the global crisis, says Andrew DeWit, a professor at Tokyo's Rikkyo University.
"Now you have this tunnel that fell apart. That has reignited enthusiasm for construction," he said. "The question is, do they have the money to spend on that?"
Press; By ELAINE KURTENBACH]
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