title: High-speed rail
context: Since their introduction, Japan's Shinkansen systems have been undergoing constant improvement, not only increasing line speeds. Over a dozen train models have been produced, addressing diverse issues such as tunnel boom noise, vibration, aerodynamic drag, lines with lower patronage ("Mini shinkansen"), earthquake and typhoon safety, braking distance, problems due to snow, and energy consumption (newer trains are twice as energy efficient as the initial ones despite greater speeds).[27]
question: Where is the fastest bullet train?
answers: Japan