My Grandfather's UFO encounter

For a time, my Grandfather was a truck driver on runs that would extend well into the night. He related to me his UFO encounter during his time as a trucker on one such night. Now, my Grandfather was man that was quick to anger, and not one to believe something unless he saw it for himself. His temperament and nature made his story all the weirder. The last person I would've expected to tell me about aliens and UFO's was him. He didn't read books and didn't seem to ever show any interest in paranormal or New Age concepts.

The year is unknown, but likely in the 1950's or 60's. The place was some lonely highway in the middle of nowhere; I don't remember which state. My Grandfather related to me that he was driving when he saw these bright lights in front of him, off in the distance. As he drove closer, he discovered it to be a gigantic UFO hovering close to ground. He described it as a huge cube that was a mile across with many lights, and glowing from underneath. Without approaching it too closely, he stopped his truck and got out to look. It was right there in front of him, blocking his way. That's when he saw them. He said he saw the aliens. Hundreds of them. When he related this story to me, his expressed his adamance to my contrarian and doubtful questions. "You didn't really see aliens!?" I asked. His emphatic response, "You better believe it! I saw them with my own eyes right there in front of me!" He described them in more detail than I can remember. I do remember him saying they where short, green and naked. I felt like that if he had the opportunity, he would've gone up and punched one of them. However, I think wisdom won the day. He never told me what they where doing or if they noticed him. Only that he decided to get the hell out of there. He drove off in a hurry. When he finally got the nerve to look back, he saw the UFO take off.