Advertisers in Tokyo gained a new medium on Tuesday -- rail cars.

The Tokyo Metropolitan Government decided to lift a ban on advertisements on the outside of the cars, which will allow railway operators in the capital to start dressing up their exteriors in October.

The move was approved by an advisory panel comprising representatives from business, academic and government sectors, and the metro government will revise relevant regulations governing advertisements in public spaces by early next month.

Trains will be allowed to cover up to 10 percent of their side walls with advertising, a space equal to 4.3 sq. meters for carriages on the JR Yamanote Line.

Up to three times that amount will be permitted for non-profit ads, such as those promoting public awareness of social issues.

Tokyo's move is expected to have a major impact on this kind of advertising, which is already allowed in the neighboring prefectures of Kanagawa, Chiba and Saitama.

Since so many lines in those prefectures run through Tokyo, operators have not been able to turn their trains into moving billboards.

"The impact of the metro government's move will be huge because Tokyo has many termini for lines in the area," said Takehisa Haneda, an official with the metro government's city planning bureau.

The JR East-affiliated advertisement agency said it is already planning to debut ads on trains on the Yamanote Line early next month.

While the agency said it has been planning to introduce such ads for years, it's timing is unfortunate.

"Given it's been just one year since the bus ads got the go-ahead (in April 2000), the impact of train ads will be smaller than it would have been," said an official of the firm.

She also said that given the public criticism bus ads have received, partly because their variety makes buses more difficult to recognize, the agency will move cautiously, probably starting with advertisements for events organized by JR group firms.