Since the Trumpeters are a protected species, contact your local wildlife agency or a wildlife rehabilitation center. They may be able to capture the cygnets, hold them safely for the winter, and place them in another safe location in the springtime away from the road. While you contact someone, keep looking to see if Mom does return. After spending a lot of time nesting, the swan parents will take a break from the kids, once they are a certain size and age to fend for themselves. So, she still may be in the immediate area. Please let us know how this works out. The Regal Swan