No, I think it's unfair. If you look at a map of the shinkansen lines in Japan, they're not just in Honshu; they span the entire length of the main islands (no

No, I think it's unfair. If you look at a map of the shinkansen lines in Japan, they're not just in Honshu; they span the entire length of the main islands (not including Okinawa, of course). They go all the way from Sapporo in Hokkaido down to Nagasaki in Kyushu, and beyond. The one to Sapporo goes through a deep tunnel under the strait. So a more fair comparison would be: why doesn't the UK have bullet trains stretching from Cornwall to northern Scotland (past Edinbugh), and another branch going to Belfast in Northern Ireland? But yeah, your point is exactly right. Density has nothing to do with why Japan has the rail network it has. It's entirely because of political will. If it were just about density, you'd only see shinkansen lines connecting the 3 major metro areas: Tokyo, Nagoya, and Kansai (Osaka/Kyoto), since they're the largest three metro areas, and they're all relatively close together. Instead, Japan is happy to build a shinkansen line even out to Kanazawa, which only has 500k inhabitants (but is a popular tourist spot), in addition to cities at the ends of the island chain (Fukuoka and Sapporo).