Amid peace negotiations between South and North Korea, the nations announced a plan to build a massive rail line connecting several cities in China and Russia to the Korean Peninsula.

Retrofitting North Korea's railways would enable increased speeds of 60 mph and heavier loads.

The larger goal could be to position North Korea as a link for trade between East Asia and Europe.

In late April, North Korean leader Kim Jong Un and South Korean president Moon Jae-in made a historic deal to end Cold War-era division. The two countries announced that they will pursue signing a peace treaty and work towards "complete denuclearization" of the Korean Peninsula. (Right now it's uncertain to what degree North Korea plans to get rid of its nukes.)

The negotiations, called the Panmunjom Declaration for peace, also include a blueprint for connecting North Korea to the world.

During the summit, Moon reportedly handed Kim a thumb drive containing a plan to build a massive railway. The preliminary plan envisions a train line that would pass through Seoul to Pyongyang in the North, then moving further on to Kaeseong and Shinuijuin, North Korea.

The ultimate plan, estimated to cost $35 billion, is much more expansive. It calls for another high-speed line from Seoul to Shinuiju via Pyongyang, along with a retrofit of six other railways crossing through North Korea.

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14 PHOTOS Inside Panmunjom, the truce village separating North and South Korea See Gallery Inside Panmunjom, the truce village separating North and South Korea South Korean soldiers stand guard at the truce village of Panmunjom inside the demilitarized zone separating the two Koreas, South Korea, April 11, 2018. REUTERS/Kim Hong-Ji PANMUNJOM, SOUTH KOREA - APRIL 11: A North Korean soldier stands guard at the border village of Panmunjom between South and North Korea at the Demilitarized Zone (DMZ) on April 11, 2018 in Panmunjom, South Korea. South Korean President Moon Jae-in and North Korean leader Kim Jong-un will meet for the first time on April 27, 2018 in the Peace House, a South Korean building inside Panmunjom. (Photo by Chung Sung-Jun/Getty Images) South Korean soldiers stand guard at the truce village of Panmunjom inside the demilitarized zone separating the two Koreas, South Korea, April 11, 2018. REUTERS/Kim Hong-Ji PANMUNJOM, SOUTH KOREA - APRIL 11: North Korean military check point is seen from an observation post on April 11, 2018 in Panmunjom, South Korea. South Korean President Moon Jae-in and North Korean leader Kim Jong-un will meet for the first time on April 27, 2018 in the Peace House, a South Korean building inside Panmunjom. (Photo by Chung Sung-Jun/Getty Images) South Korean soldiers stand guard in the demilitarized zone separating the two Koreas, in the truce village of Panmunjom, South Korea February 7, 2018. Picture taken on February 7, 2018. REUTERS/Josh Smith PANMUNJOM, SOUTH KOREA - APRIL 11: A North Korean national flag in North Korea's propaganda village of Gijungdong is seen from an observation post on April 11, 2018 in Panmunjom, South Korea. South Korean President Moon Jae-in and North Korean leader Kim Jong-un will meet for the first time on April 27, 2018 in the Peace House, a South Korean building inside Panmunjom. (Photo by Chung Sung-Jun/Getty Images) A South Korean soldier stands guard at the truce village of Panmunjom inside the demilitarized zone separating the two Koreas, South Korea, April 11, 2018. REUTERS/Kim Hong-Ji A North Korean soldier is seen through a door on the North side of the border truce village of Panmunjom in the Demilitarized Zone (DMZ) dividing the two Koreas on April 11, 2018. North Korean leader Kim Jong Un and South Korean President Moon Jae-in are due to meet on April 27 at the South's side of the demilitarized zone for the landmark inter-Korean summit. / AFP PHOTO / Jung Yeon-je (Photo credit should read JUNG YEON-JE/AFP/Getty Images) A South Korean soldier stands guard at the truce village of Panmunjom inside the demilitarized zone separating the two Koreas, South Korea, April 11, 2018. REUTERS/Kim Hong-Ji South Korean soldiers work on a barricade on the Grand Unification Bridge which leads to the truce village Panmunjom, just south of the demilitarized zone separating the two Koreas, in Paju, South Korea, January 19, 2018. REUTERS/Kim Hong-Ji South Korean soldiers stand guard in the demilitarized zone separating the two Koreas, in the truce village of Panmunjom, South Korea, February 7, 2018. Picture taken on February 7, 2018. REUTERS/Josh Smith The general view shows a North Korean village near the truce village of Panmunjom, seen from within the Demilitarized Zone (DMZ) separating North and South Korea on February 21, 2018. / AFP PHOTO / Ed JONES (Photo credit should read ED JONES/AFP/Getty Images) North Korean soldiers walk beside the road leading to the North Korean side of the truce village of Panmunjom, seen from within the Demilitarized Zone (DMZ) separating North and South Korea on February 21, 2018. / AFP PHOTO / Ed JONES (Photo credit should read ED JONES/AFP/Getty Images) This general view shows a North Korean miltary post on the road to the truce village of Panmunjom, seen from within the Demilitarized Zone (DMZ) separating North and South Korea on February 21, 2018. / AFP PHOTO / Ed JONES (Photo credit should read ED JONES/AFP/Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

Currently, the rails in North Korea break periodically under heavy loads, and the trains can only travel about 30 miles per hour on average. Modernizing the lines would double speeds.

The railway could become much more than a transportation megaproject. As CityLab notes, it's an important geopolitical move that could entice the North Korea's regime to keep its promises for peace, because it would incentivize more trade between the Korean Peninsula, China, and Europe.

That's because the rail lines would ultimately connect the Shinuiju-Dandong crossing — the center of North Korea's commerce with China — Russia’s Trans-Siberian Railroad, South Korea’s two largest cities (Seoul and Busan), North Korea’s third largest city (Chongjin), and its industrial zone with the highest GDP per capita (Rajin).

Whether it will actually be built is still unclear. Another iteration of the inter-Korean railway plan has existed since the early 2000s, and in 2007, North and South Korea did a test run for the rail link, with two trains crossing the demilitarizered zone. The fraught relationship between the two countries, however, halted further development.

If completed, however, the project has the potential to transform transit, trade, and political relations on the Korean Peninsula.

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