The Construction Ministry said Thursday it will set up antennas in more than 200 tunnels on highways and national roads nationwide over the next five years to enable transmission for cellular phone use.
The ministry plans to invest more than 24 billion yen in the project beginning next April, officials said.
The ministry says it felt the need to ensure cellular phone communications to report traffic accidents and other emergency situations.
According to figures from Kanagawa and Shizuoka prefectures, where the Tomei Expressway runs, some 80 percent of all emergency calls were made from mobile phones.
The ministry is planning antennas in 206 of the nation's roughly 400 tunnels longer than 200 meters in areas where cellular phone carriers offer service.
Cellular phone firms have already installed antennas in 67 expressway tunnels in the Kanto region.
The expenses are expected to be split by the cellular phone firms and the government or the semigovernmental Japan Highway Public Corp.
The Construction Ministry might ask the Posts and Telecommunications Ministry for financial support in areas where phone companies consider the project "unprofitable."
Because the antennas would be connected to optical fibers under the control of government or semigovernmental bodies, fees for them can be lower than those for antennas installed by private firms.
The ministry, however, will strictly limit the use of cellular phones to passengers, because the Road Traffic Law bans drivers from making calls while driving.