Ridesharing/carpooling is a great way to get to and from the music, while impacting the Earth less and building community. I've made some of my best concert-going friends from using rideshare services. I recommend checking out the following:
-SpaceShare builds custom rideshare systems. Encourage festivals, conferences or other events to use their system to share rides at SpaceShare (http://www.spaceshare.com) and you'll get a ride from neighbors who like the same music.
For city-to-city carpooling, sites like craigslist (http://www.craigslist.org) and erideshare.com also be practical no matter where you live in the world or US.
You can also look into car sharing programs, if you are a resident, in places like San Francisco with companies and organizations like Flexcar and citycarshare. Other major US and European cities have similar schemes.
It really seems greening up transportation isn't that hard, especially with ride-share and car-share opportunities...