Rides to Trailheads for One-Way Runs/Hikes/Rides

Oftentimes I'll find myself thinking "I'd really like to do a one-way run on Trail XYZ, but I can't find anyone to drop me off and wait for a few hours to pick me up." Then I'll see someone on trail and wonder if they were doing it the other direction or the same direction. All that kept our respective one-way runs or hikes from happening was that we didn't know each other. I assume this happens a lot to people that do trails on their own.

But that's why we have Intarweb! There are various carshares and rideboards online along the spectrum of commercialness and formality. Why not for this? (Or does it already exist? If so, enlighten me.) I'm a web idiot and I'm in medical school, so if anyone does set this up, it won't be me. But it would be WAY cool because it would solve this problem and you'd meet people, and here's what it might look like:

1) Prescreening of participants. You want to have some accountability so it's not just hitchhiking and the only difference between the creepy guy picking you up on I-5 and the creepy guy picking you up at the trailhead is that the latter was able to sign up for an anonymous email. Maybe make it reference-based at the beginning like Gmail. Maybe use a phone call-back feature like some web services do. Large group meetings in advance work well but they also take time that people don't have.

2) Track features offered by ridesharers. Imagine a checklist on the sign-up. Some people will want a child seat in the car, or a bike rack, or a driver who doesn't mind dogs. For safety, some people might like to have someone else with them while they do the trail.

3) Enforce karma. For those people with cars, it won't do to have one core of nice people constantly offering rides, and other folks never returning the favor. The system could track who gives and who receives. Another possibility is that people could trade on their own - "Sure, I'll do it for $10." "Sure, I'll do it for five power bars. "Since I'm a landscaper, I'll trim your rosebushes for three rides."

Just a thought. It would also be great for people traveling, who could learn about the cool trails before they even show up.