If you're interested in sustainable travel options, (see my last post here ) there's much more to learn. A great source is at the International Ecotourism Society's website, here.
For travelers who share my concern about effects of their travel on climate change, here's a more scholarly paper: Kockelman et al. 2008;TRAVEL CHOICES AND THEIR RELATIVE CONTRIBUTIONS TO CLIMATE CHANGE: WHAT BEHAVIORAL SHIFTS WILL BUY US
An article in Science Daily extends this a bit further: http://www.sciencedaily.com/releases/2013/06/130617111345.htm
Then, of course, there are other options such as foot travel, bicycling, etc. The Alternative Travel Project - here - gives some other options.
And maybe it's incredibly obvious - but some of us just choose to stay home.