TOKYO (AP) — North Korean leader Kim Jong Un's decision to take a train to his summit in Russia's far east hints at the potential of a bigger dream held by many in Asia: unimpeded travel by rail from the southern tip of the Korean Peninsula to Moscow and beyond.

The benefits range from bolstering regional cooperation to slashing costs and travel durations. But with sanctions and distrust standing in the way, it could be a long time before any trains working their way north from Seoul will be passing through Pyongyang Station.

After a day of talks with Russian President Vladimir Putin on Thursday, Kim boarded his trademark green-and-yellow carriage for the trip back across the two countries' shared border and on to Pyongyang.