While in PARK, my 2023 Nissan Titan inexplicably started rolling away as I was getting my mail from my mailbox. It traveled down my driveway, over a railroad tie border, deflected off of a tree, and eventually came to a stop when it became wedged under a pine tree. The wheels were turning. The vehicle was not sliding. There was snow and I recorded the impressions of the tire tread in the snow. Furthermore, when I got into the vehicle to back it out, the vehicle's shifter was still in PARK. I put it in reverse, backed it out from under the tree, and was able to drive it to my parking pad. The vehicle is available for inspection. My safety was put in risk because the only thing I could have done is chase after and attempt to jump back into the driver's seat (the door was still open). I thought better of taking such a risk and did not do so. Had my children been outside, they could have been run over by my truck. They would have had no idea I wasn't driving it, and -- as stated -- the truck drove itself over the railroad tie and into my yard. The problem has not been reproduced, but Nissan had a recall of similar vehicles that took multiple attempts to replicate. The vehicle has been inspected by the manufacturer (Nissan), and Nissan has said they are not at fault. The Titan has also been inspected by my insurance company. There were no warning lamps, and no warning of any type. I heard the crunching snow on the way back from my mailbox, looked at where the n