If all goes according to plan, you might be able to travel all the way from London to Japan by rail.

Yes, Japan. As in, the island nation.

Russia recently announced its proposal to bring the Trans-Siberian Railway to Tokyo.

The project would involve building two extensions of the railroad. The first would connect the province of Vladivostock with the Russian island of Sakhalin, while another 28-mile-long bridge across the Sea of Japan would connect the railroad with Hokkaido, Japan’s northernmost island. From Hokkaido, it’s about four hours by bullet train to Tokyo.

Russia is seeking Japan’s cooperation in regards to technology and other aspects of extending the Trans-Siberian Railway.

This isn’t the first time Russia has tried to connect its rail service to the Sakhalin Islands. In 1950, tyrannical Russian premier Josef Stalin started the construction of a tunnel to connect the mainland to the islands via rail. After Stalin died three years later, the construction was suspended. But interest in making the connection has been rekindled by Russian President Vladimir Putin.

“If the extension is realized, the Trans-Siberian Railway would be filled with freight [trains]. That’s because the railway is connected with Japan.” Putin said in 2011.

But there’s one major obstacle: the difference in width of railway tracks between Japan and Russia.

The width of Japanese rail lines is 106.7 centimeters (about 42 inches), whereas the Trans-Siberian Railway’s track width is 152.0 centimeters (about 60 inches). This means that Japanese and Russian trains cannot operate on one another’s lines.

Sure, containers can be moved from Russian trains to Japanese trains, but 40-foot cargo containers can’t fit through tunnels in Hokkaido. In the rest of Japan, they can only pass through tunnels between Tokyo and Morioka.

“The possibility that the extension of the Trains-Siberian Railway to Hokkaido is realized is zero,” Hisako Tsuji of the Economic Research Institute of Northeast Asia told the Asahi Shimbun. “Even if [big] tunnels are dug for these containers, transport on the railway is not cost-effective.”

Since 80 percent of Japan’s imports from Russia consist of liquefied natural gas, which is transported by vessels from ports in the Russian Far East, the odds are good that Tsuji is right about using the railway for cargo.

However, if passenger rail service between Russia and Japan is the goal, extending the Trans-Siberian Railway to Japan could be a great idea.