The calculated distance (air line) between Yotsukaidō and Ryūgasaki is approximately 17 miles respectively 28 kilometers.
By car or train, the actual journey to Ryūgasaki is certainly longer, as only the direct route (as the crow flies) between Yotsukaidō and Ryūgasaki has been calculated here.
Air line (approximately)
28 kilometers
15 nautical miles