The writing on the back of this card says so ."Going-to-the-Sun Road winds across the Continental Divide at Logan Pass.It is the only road in Glacier that connects the west and the east sides of this park.The 52 mile long drive offers some of the most spectacular scenery accsseible by car in the United States."
And Wiki says so :
Going-to-the-Sun Road is the only road through the heart of Glacier National Park in Montana, USA. It was completed in 1932, and it is the only road that crosses the park, going over the Continental Divide at Logan Pass. A fleet of 1930s red tour buses "jammers", rebuilt in 2001 to run on propane or gas, offer tours on the road. The road, a National Historic Landmark and a Historic Civil Engineering Landmark, spans 53 miles (85 km) across the width of the park.
The road is one of the most difficult roads in North America to snowplow in the spring. Up to 80 feet (25 m) of snow can lie on top of Logan Pass, and more just east of the pass where the deepest snowfield has long been referred to as Big Drift. The road takes about ten weeks to plow, even with equipment that can move 4000 tons of snow in an hour. The snowplow crew can clear as little as 500 feet (150 m) of the road per day. On the east side of the continental divide, there are few guardrails due to heavy snows and the resultant late winter avalanches that have repeatedly destroyed every protective barrier ever constructed. The road is generally open from early June to mid October.
The two lane Going-to-the-Sun Road is quite narrow and winding, especially west of Logan Pass. Consequently, vehicle lengths over the highest portions of the roadway are limited to 21 feet (6.4 m) and that means no recreational vehicles or trailers in excess of this length restriction are permitted beyond two larger parking areas, each located at lower points dozens of miles below Logan Pass, on both the west and east sides of the parkway.
Prior to the construction of the road, it would take the earliest visitors 3-4 days to see the park.