I was driving east on i-8 near piedra, az. returning from san diego area. i had been looking up at the moon, which was about to be a super moon in the next day or so. i noticed a light on the south side of the highway, which was approximately 2-3 feet in size, 75-80 ft away, about 8-10 ft. in front of me (on the side though, in the desert). i was in the far right lane and this light just continued to keep up with my driving speed. at first we thought it was coming off the truck in front of me, so i passed the truck. it disappeared for a minute and then returned in the same spot. it was just a beam of light moving on the desert landscape, same direction, same speed as my car. it was too bright to be a reflection off of anything. one of my passengers stuck her head out the window, thinking a helicopter was flying over, but there wasn't anything. i alerted my other passenger, she agreed, she saw it too. we watched it and it continued "following" us (really, leading us). the light continued for approximately 15 minutes and then disappeared when we turned onto hwy. 85, near gila bend, az. in hindsight, i wished i pulled over and stopped my car to see what it did, but didn't. i was traveling approximately 75-80 miles per hour on the highway. i felt strange while seeing it and it took awhile before i thought that maybe it was an ufo. i never had that experience before. when i got home and googled gila bend and ufo's i had chills running down my body, which i've never had like that before.