A recent World Bank report on high-speed rail systems around the world noted that ridership forecasts rarely materialize and warned that "governments contemplating the benefits of a new high-speed railway, whether procured by public or private or combined public-private project structures, should also contemplate the near-certainty of copious and continuing budget support for the debt."
That's certainly what happened in Japan, where only a single bullet-train line, between Japan and Osaka, breaks even; it's what happened in France, where only the Paris-Lyon line is in the black. Taiwan tried a privately financed system, but it ended up losing so much money that the government had to bail it out in 2009.