Why is Kim Jong Un traveling to Russia by train?

As North Korea's Kim Jong Un used a dark green train to travel to Russia on Tuesday (September 12), former North Korean official described the vehicle to Reuters. Special advisor to South Korea's Unification Ministry Ko Young Hwan has been on the train of the North's founder Kim Il Sung. Since becoming leader in late 2011, Kim has used a train to visit China and Vietnam, as well as his previous trip to Russia to meet Putin in 2019.