This was something that I've never been able to explain, so I'm posting this here just in case it was something truly anomalous. My mother and I were at an evening Bat program put on by the rangers at Carlsbad Caverns. Around 8:30, the program ended and the cars left the parking lot. We waited until all the other cars were gone (maybe around 8:45) and it was getting dark before we left. We were the only car on the road as we made our way back into Carlsbad (route 180)on a two-lane highway. Around 9 pm, I noticed a bright white/yellow orb about the size of a basketball (perhaps larger) approach the car from the behind (it followed the road, but approached rapidly). The light stopped very close to the bumper (there was maybe half a car length between us and the object). I at first thought it was a motorcycle and I thought it was weird that they were so close to the bumper and that the person did not try to pass us since there were no other vehicles on the road. The object followed the car at the same speed for a minute or so when I decided to roll down the window. There was no sound other than our own car (no loud motorcycle engine noise either). At one point, my mom turned on the brights of our car and a smaller light underneath the larger orb appeared as she did so (it was rectangular and yellow about the length of a pencil). A few moments later, a car approached in the other lane with its headlights on. My mom turned off her brights and the smaller light under the object "turned off" as well. I waited for the headlights of the approaching car to illuminate the road behind us so I could see if this was a motorcycle. Just as the other car's headlights were about to light the road where the object was, the orb dimmed quickly and was gone. The lights of the approaching car clearly lit the road, but there was nothing behind us: no motorcycle, no car, nothing. There wasn't anyone on the shoulder (which was actually lined by cones) and no one was in the other lane. It simply vanished and was not seen again. The light appeared to reflect off the road and it was bright, but not blinding. I could not see it attached to any vehicle. It traveled smoothly and followed the road. It was only a few feet off the ground as it was clearly seen out the back window of our SUV. The time was now about 9:10 pm. We both thought it was weird and neither of us could explain where the light went and what it was. To this day, I wonder about it and have had a few other sightings here and there, but this was the first one of something that I can only describe as "odd." I've told one to two people about this, both of who laughed in my face. I toyed with the idea of submitting this for a while because I don't want to freak out over something that might not be significant after all. At the time, I felt calm because I thought it was a motorcycle. As the incident progressed, I felt uneasy and curious. I still wonder what it was.