The Bullet Train
新幹線大爆破 (original)
One of the Japanese Shinkansen “Bullet Trains” is threatened with a bomb that will explode automatically if the train slows below 80 km/h, unless a ransom is paid. Police race to find the bombers and to learn how to defuse the bomb.
Starring Ken Takakura, Shinichi Chiba, Kei Yamamoto, Eiji Gō, Akira Oda, Raita Ryu, Masayo Utsunomiya, Ken Utsui, Yumiko Fujita, Yumi Takigawa
Watch "The Bullet Train" on Amazon released in 1975. It's a crime and drama movie, and has a rating of 6.8 out of 10 from Imdb which is usually fine for this kind of movie, and is currently only available for purchase or rent.