I was recently thinking about carpooling and how it has evolved over the past decade or two. Carpooling used to be something you could only do in person. You had to know someone (co-worker, neighborhood or family member) who happen to be going in the same direction.
Then came ridematch databases that matched people within a certain employer or area. Sure, you did not know the person, but you could take comfort in that they were like-minded and employed.
Today, you can arrange carpooling online at http://www.goloco.org/ and http://www.erideshare.com/. These services allow for all types of trips (e.g. employee, special events, grocery store) in real time using your Internet phone. The online carpooling is just in the infancy stage, but you can imagine in 20-30 years when 15% of an urban area is looking for a ride. One thing all of this traditional carpooling has in common is that it involves prearrangement through some mechanism, such as online or work-based matching. Still, the future seems to hold the prospect of a system designed around carpooling without prearrangement (two types of carpooling without prearrangement have been going on for some time in Washington D.C. and San Fransisco). This is called fexible carpooling. Learn more about it here.