Millions of Chinese cram onto trains to make the annual pilgrimage home for the Lunar New Year holiday. It’s a crowded and often uncomfortable experience that is rapidly being transformed by the country’s push into the world of high-speed rail. China already has the globe’s longest bullet-train network, but it’s plowing 3.5 trillion yuan ($556 billion) into expanding its railway system by 18% over the next two years, to 150,000 kilometers, or more than 93,000 miles.