Sepulveda Pass: 3 Weeks
Sepulveda Pass: 2 Months
Tejon Pass: 3 Weeks
Saw that these signs were still up on my latest swing through Southern California. Although there's an undeniably random factor in how long signs will stay up, here are some basic rules:
Smaller, obliquely placed signs will stay up far longer than large, spectacular ones. A sign need only be as big as it takes to get its message across.
The harder it is for the viewer to physically reach the sign, the longer it'll stay up.
These signs were placed on divided highways, visible only to those going in the opposite direction. To physically reach them would require miles of driving, both to get to the sign itself, and then to get back to the way you were originally going. Hanging them, however, required little more than pulling over and hammering in a couple of nails.
The ability to exploit these kinds of dynamics is one of the many things that makes this job so fun and interesting.