The Canadian Pacific Railway was instrumental in Banff's early years, building the Banff Springs Hotel and Chateau Lake Louise, and attracting tourists through extensive advertising. In the early 20th century, roads were built in Banff, at times by war internees from World War I, and through Great Depression-era public works projects. Since the 1960s, park accommodations have been open all year, with annual tourism visits to Banff increasing to over 5 million in the 1990s. Millions more pass through the park on the Trans-Canada Highway. As Banff has over three million visitors annually, the health of its ecosystem has been threatened. In the mid-1990s, Parks Canada responded by initiating a two-year study which resulted in management recommendations and new policies that aim to preserve ecological integrity.