Define a Shared Vision
SAP employees focused on changing their commuting patterns in advance of the 2010 Olympics in Vancouver. They report that the changes stuck and more than 2/3's "use alternative commute methods."
Claudia Girrbach has an article in GreenBiz about 5 employee engagement efforts at 5 different companies. I am borrowing the ideas for comment here. (this is 2 of 5)