The calculated distance (air line) between Hitachi-Naka and Mitsukaidō is approximately 40 miles respectively 65 kilometers.
By car or train, the actual journey to Mitsukaidō is certainly longer, as only the direct route (as the crow flies) between Hitachi-Naka and Mitsukaidō has been calculated here.
Air line (approximately)
65 kilometers
35 nautical miles