Railroads have played an important role in New England ever since the Granite Railway, America's first commercial railway, began operations in Massachusetts in 1826. As industrialization spread across the region, hundreds of railroads were built throughout the 19th century. Railroad mileage peaked around World War I, and from that point on mileage began to shrink. Despite this, railroads continue to be important for freight and passenger transportation in the region, with the New Haven Line holding the title of busiest railroad line in the entire United States.