narrow gauge: 112 km 1.000-m gauge (112 km electrified); 1,211 km 0.950-m gauge (153 km electrified) (1998)
Jamaica:
total: 370 km
standard gauge: 370 km 1.435-m gauge; note - 207 km belong to the Jamaica Railway Corporation in common carrier service, but are no longer operational; the remaining track is privately owned and used to transport bauxite
Japan: total: 23,670.7 km
standard gauge: 2,893.1 km 1.435-m gauge (entirely electrified)
narrow gauge: 89.8 km 1.372-m gauge (89.8 km electrified); 20,656.8 km 1.067-m gauge (10,383.6 km electrified); 31 km 0.762-m gauge (3.6 km electrified) (1994)
Jersey:
0 km
Jordan:
total: 677 km
narrow gauge: 677 km 1.050-m gauge (2000)
Juan de Nova Island:
total: NA km; short line going to a jetty