If, like me, you use public transportation, you know how frustrating it can be to fruitlessly wait at a bus or train stop while an endless procession of half-empty cars whizz past. Hitching a ride in one would be great, but trying to thumb down a ride is tough (and dangerous). A company launching this morning at DEMOfall hopes to bring some technology to the equation, and create a modern form of hitching.

Mapflow’s Avego is a service for mobile devices — starting with the iPhone — that will attempt to pair up passengers and drivers, using a combination of GPS location, messaging and a web interface to help plan out trips. Passengers will be automatically billed for gas money, and will be able to plan trips out ahead of time or request one at the moment that they need it.

As good ideas go, Avego is pretty high on the list. Few things as common as car ownership in the United States, but many are interested in ditching their ride in favor of alternate options. Recent statistics have shown that fewer young people are getting licenses.

However, none of that means that the company is destined for success. Without a very large, involved userbase, it will be hard to make Avego reliable, and it’s always difficult to coax people into dealing with strangers. My feeling is that the application could get some traction along heavily trafficked long-distance routes like San Francisco to Los Angeles, or New York to Washington, D.C. Drivers taking those trips feel the sting of $4 gas, and many are already looking for passengers to help defray the cost. At the moment, many use Craigslist, but Avego could work better.

But for a trip within a city, having someone pay you some spare change to cover the gas cost for going a few blocks isn’t likely to attract a lot of drivers. Luckily, there are some options that should make the service more driver-friendly, like being able to restrict passengers to only kids from the same college you go to, or to women only for female drivers. Both drivers and passengers can also rate each other.

Whether it proves successful or not, Mapflow is only one of a new generation of startups aiming for alternatives to car ownership. There is also HopStop, which helps schedule public transportation, Intrago, which wants to set up bike rental stations in cities, and several other ridesharing applications, including GreenRide, NuRide and RideStation.