You may have seen the billboard, heading back from the airport on that winding stretch of Hiawatha Avenue that hasn't yet been turned into a semi-freeway: "STOP the Reroute," it says in a multicolored script nestled amid pictures of trees and a kindergarten sun. It's almost heart-wrenching in its assumption that, if people only knew, the powers that be would listen. In fact, chances are that the grassroots movement behind the billboard will fail, and the Minnesota Department of Transportation will go ahead with its $39 million plan to build a new, four-lane Hiawatha through the urban wilderness adjacent to Minnehaha Park--never mind that when it's all done, the new road will slice a mere three minutes off the average downtown-to-airport trip. After almost 40 years of planning, the engineers say, it's too late to turn around. But for just a minute as you drive past the billboard, it's tantalizing to dream of what could happen if people only knew.