By Agence France-Presse
The two Koreas last month agreed to start the survey no later than late October and to hold the groundbreaking ceremony sometime between late November and early December, as the countries pursue a reconciliation drive.
But the possibility of the project running up against UN sanctions imposed on North Korea over its nuclear programmes has caused delays.
"It is significant that this project has received support from the United States and international community", said Kim Eui-Gyeom, spokesman for the presidential Blue House in Seoul.
Railway experts from both sides will criss-cross the country on survey trains together, Kim said in a statement, adding that the process will "bring inter-Korean cooperation to a new level".
Yonhap news agency said the South was expected to bring fuel for train locomotives, and other unspecified materials for the survey in the North.
Delivering fuel to North Korea could potentially have been in breach of a UN cap limiting imports to 500,000 barrels a year.
US Secretary of State Mike Pompeo said Tuesday any inter-Korean rapprochement had to move forward "in tandem" with efforts to denuclearise the peninsula, and could not come sooner.
US president Donald Trump and North Korean leader Kim Jong Un held a historic summit in Singapore earlier this year, signing a vaguely worded deal on denuclearisation.
But since then, talks on denuclearisation have stalled, with meetings either deemed unproductive, pushed back or cancelled altogether.
The US and South Korea have launched a working group to make sure that they don't "talk past each other", Pompeo said, as Seoul and Pyongyang appear to be moving ahead with their rapprochement more quickly than Washington and the North are making headway on nuclear disarmament.
A second leaders' summit is expected to take place in early 2019, according to Washington.
In the meantime, North and South Korea have made several concrete decisions on reconciliation and exchanges.
But the implementation of cross-border projects such as the reconnection of railways have been hamstrung by the lack of progress in denuclearisation talks.