I was on my way to work on I-10 in Phoenix Az. and witnessed @18:00mst a bright orange fireball streak from west toward the east. It appeared this fireball fell to the earth but may have just travelled out of the horizon and my view. But it appeared to me that the thing was falling as it streaked accross the sky. I originally thought it was a helicopter that had caught fire and was crashing to the ground. Due to its west to east travel and downward descent, I soon realized this wasnt the case.