Riding along in Pennsylvania, a few giant windmills loom on a mountain nearby. It's only the latest example of clean energy opportunities we've witnessed this week.
Clearly, wind power is a big part of any effort to achieve energy independence and cut carbon emissions. As is hydroelectric power -- and there is no greater demonstration of the potential there than Niagara Falls.
Rail travel itself is a "clean" method of personal and commercial transportation. So it's been interesting to see some other opportunities outside our windows here.