Photo/Illutration Staff inspect a bridge using a drone in Kimitsu, Chiba Prefecture. (Provided by Kimitsu city government)

Nearly 80,000 tunnels, bridges and other vital components of the nation's road infrastructure are in a dire state and badly in need of repair, the government says.

The figure represents nearly 10 percent of the entire road network, and poses a massive challenge as most of the repairs need to be accomplished within five years.

A survey by the Ministry of Land, Infrastructure, Transport and Tourism, which covered 770,000 bridges, tunnels, pedestrian overpasses and other road infrastructure, identified 80,000 projects in need of repair due to problems such as corrosion and cracks.

Fiscal difficulties facing local governments, which are responsible for managing their areas of the road network, mean that almost 80 percent of the repairs have still to be carried out.

To eliminate delays in the work, the ministry established a subsidy system totaling 222.3 billion yen ($2 billion) to be given to local authorities for effective maintenance and repairs.

The funds are to be earmarked in the budget for the next fiscal year.

The project is daunting in scale. In 2012, concrete slabs fell from the ceiling of the Sasago tunnel on the Chuo Expressway in Yamanashi Prefecture, killing nine people after their vehicles were crushed.

In response to the accident, the central government ordered that the nation's bridges, tunnels and other road infrastructure to be inspected every five years starting from 2014.

Most local governments, working with construction companies nationwide, managed to complete the first inspection by the end of fiscal 2018.

The results of these inspections, with each item of infrastructure classified in four phases, were released last summer.

According to the results, 68,369 bridges, or 9.5 percent of the roughly 720,000 total, need repairs within five years in what was labeled as the “early measures phase.”

A further 682 bridges were deemed to be in such a state as to require prompt action, which includes closing roads, in what was labeled the “emergency measures phase.”

The survey found that 4,353 tunnels, or 40.9 percent of the roughly 10,000 total, need repairs within five years, while 63 tunnels were deemed to be in need of urgent work.

An additional 40,000 items of infrastructure, such as pedestrian overpasses, were in a similar state, the survey found.

As of the end of fiscal 2018, it said 53,694 bridges, or 77.8 percent of the structures needing repairs, had not been fixed.

It said 2,812 tunnels, or 63.7 percent of those needing repair work, were in the same situation.

Roughly 90 percent of infrastructure that needs repair work is the responsibility of prefectural governments or local municipalities. A lack of financial resources, coupled with opposition from residents over certain projects, have hindered demolition and repair work on aging infrastructure.

A manpower shortage is another factor.

Of the 689 towns that responded to the ministry’s survey, 20 percent said they did not have an engineer on staff who could make plans for an inspection and repair work.

Of 160 villages contacted, 60 percent gave the same response.

Bridges constructed 50 years ago or earlier are considered “aging.” The ministry said structures in this category will increase dramatically in the near future, from 27 percent in fiscal 2019 to 52 percent in fiscal 2029.

Tunnels in that category are also expected to rise from 21 percent to 35 percent during the same period.

To prepare for this eventuality, the ministry in fiscal 2015 established a system to subsidize about half of all repair costs.

Hikaru Nakamura, a professor of civil engineering at Nagoya University's Graduate School of Engineering, urged local governments to create effective operational and maintenance plans "that include demolition and consolidation of infrastructure.”

(This article was written by Yosuke Watanabe and Yuki Okado.)