Cool way to carpool by swapping car keys and then each using the others car when you are done your trip.

Yep, I haven't done it but some friends I know have.

Is there a name for it?

We do the Lost Coast like this. Two groups hike in from each direction. We meet in the middle and do the key exchange. Then we drive each others cars back to Garberville for the post hike meal and swap back. Works great. We just call it a key swap.

Some people at portlandhikers.org did that from two ends of the Columbia Gorge

It's better to drive to the trailhead in the other party's car, so that after each finishes the hike they can just go home in their own vehicles, and exchange keys later on. That way, if there are delays, nobody is stuck waiting at the meeting place.

It's a great system but can backfire if something goes wrong. I tried this with a Portland-area couple in the Wind Rivers. It would have worked fine except that my dog got sick and I had to abort my trip. I camped along the trail a few miles from the trailhead to rest the dog. The couple finished early and got by me without my seeing them, so when I got back to the trailhead, their vehicle was gone and they were halfway back to Oregon! I found someone who was going out who agreed to call the couple for me from Pinedale (no cell phone reception at the trailhead) and they sent the Great Outdoors Shop shuttle to rescue me.

Really good point. I wonder if there is a way to mitigate this problem.

One point here is that you could always plan B it and shuttle/hitchhike back to your car but it is sketch if someone (or some dog) in your party is sick.

It can work but you better trust the other party – and know if your insurance allows it. For a couple of years I couldn't let anyone else drive my truck due to the insurance I had – I was covered under my at-the-time boyfriend's USAA insurance and he was the only one besides me allowed to drive my vehicle. Once we got married they gave me full coverage and that restriction went away. But having said that….I have to really, really trust someone to let them drive my vehicles and the same back – if you wreck the car god forbid it could be painful.

We call them key exchange hikes, but Sierra Club national supposedly does not allow them anymore or at least Dallas Sierra Club stopped allowing it.