The calculated distance (air line) between Sŭngho 1-tong and Ongjin is approximately 80 miles respectively 129 kilometers.
By car or train, the actual journey to Ongjin is certainly longer, as only the direct route (as the crow flies) between Sŭngho 1-tong and Ongjin has been calculated here.
Air line (approximately)
129 kilometers
70 nautical miles