麻烦谁能帮分析下句子成分啊?Of major concern to Amtrak and its advertising

麻烦谁能帮分析下句子成分啊?
Of major concern to Amtrak and its advertising agency DDB Needham,were the long-distance western routes where ridership had been declining significantly.
这句话原文是
Amtrak(美国铁路客运公司) was experiencing a downswing in ridership(客运量) along the lines comprising its rail system.Of major……declining significantly.