US driver licensing laws vary by state. Many states allow 15 year olds to obtain what is called a learner’s permit, allowing them to drive under certain conditions, which typically include having an adult with them. This was true of Florida, where I learned to drive, and I would expect it to be true of Montana, where low population densities and long travel distances increase the importance of driving compared to more urbanized areas. (Some states require would-be drivers to wait until they are 17.) Florida did not allow 15 year olds to drive at night; I don’t know whether that is true in Montana.

Based on the news report, I’d put full blame on Mr. Tenley here. Dressing up in a costume that is specifically designed to make you hard to spot, and then walking onto a major highway like US 93 at night, is Darwin Award worthy.