Few doubt Prime Minister Shinzo Abe's decision to invest public funds in a $90 billion high-tech maglev railway makes political sense. Whether it makes equally good economic sense is less clear.

Proponents say lending government money to Central Japan Railway Co. (JR Tokai) to speed up the launch of a service linking Tokyo and Osaka with a high-speed, magnetically levitated train will spark growth in an economy still fragile after three years of an Abenomics mix of hyper-easy monetary policy, spending and promised structural reforms.

But critics counter the government is targeting the plan mainly because it has a big price tag, and doubt its economic impact and export potential.