But critics say the South risks conceding some of its conventional military strength before North Korea takes any meaningful steps on denuclearization, as the larger nuclear negotiations between Washington and Pyongyang seemingly drift into a stalemate.
In mid-January, North Korea reported its first arms test in almost a year, a gesture that increased the pressure to revive the stagnant dialogue with Washington.
Before the South Korean train headed for the North on Friday, a farewell ceremony was held at Dorasan Station, just south of the border in Paju, Gyeonggi. The incident did not trigger any gunfire, unlike past year when a North Korean soldier ran across under a hail of bullets from his own side.
The US has given its support to the rail survey, but Mr Moon will have to have a number of hard conversations if he's to persuade President Donald Trump that easing sanctions at this stage would be worthwhile so the project can go ahead, our correspondent says.
When asked Saturday if he would ever host Kim in the United States, Trump replied: "At some point, yeah".
However, she added that Trump and Moon agreed that "vigorous sanctions" need to be maintained so that North Korea understands that denuclearisation is the only option.More news: Raptors' Kawhi Leonard agrees to endorsement deal with New Balance
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- Kim visit to Seoul this year?
However, differences have emerged between Washington and Seoul on how to proceed with Kim, as the dovish Moon has long favoured engagement with the North.
The Koreas will run trains on two railways for 18 days starting Friday, South Korea's Unification Ministry said in a Wednesday statement.
They have also begun work to reconnect a train line and fix another rail link across the border. Trump has said he hopes to meet with Kim early next year in a bid to give the talks a boost.
The railway survey marks another follow-up to the Pyongyang Declaration signed by South Korean President Moon Jae-in and North Korean leader Kim Jong-un in late September during their third summit, in which they agreed to pursue "substantial measures" to develop the nations' economies in a "balanced manner".
As a gesture towards reconciliation, the two Koreas reconnected the western line in 2007 and limited numbers of freight trains transported materials and goods to and from the Seoul-invested Kaesong industrial zone in the North for about a year.