Tokyu has more than 100 kilometers (64 miles) of railway tracks serving 2.2 million people a day, including commuting "salarymen" and "salarywomen" and schoolchildren in uniforms.
Since the nuclear disaster in Fukushima, when a tsunami set off by a massive earthquake sent three reactors into meltdowns, Japan has shut down most of its nuclear plants and ramped up use of coal-fired power plants.
The country aims to have 36%-38% of its energy come from renewable sources by 2030, while slashing overall energy use.
Tokyu Railways has sought to publicize its effort with posters and YouTube clips.