[1] The project which is codenamed the "Eastern Kanagawa Rail Link" began its infancy from the Transport Policy Review Forum [ja] in January 2000.
However, as the population decline led to ridership drop of Sōtetsu, the rail company became more favorable towards the plan which improves connectivity with the Tokyo Metropolis and Saitama Prefecture.
In September 2004, the Sōtetsu–JR Link Line plan was formally announced which would provide a more direct access to Shinjuku, Tokyo from areas served by Sōtetsu between Nishiya and Ebina.
[2] In May 2005, the Urban Railroad Convenience Improvement Act [ja] was passed by the parliament of Japan and went into effect on 1 August 2005 with the aim of encouraging many different railway operators of major metropolitan areas of Japan to provide better and more convenient passenger experience via new railroads which would enable through services between different operators.
This was due to the high cost of construction and the drop in estimated ridership from the initial projection, resulting from the COVID-19 pandemic.