Good post.
The following is MOO
I used to live off the 91 and took the 91 and 55 daily. You are correct that there are a lot of locals commuting to work. However, There are a few things I can think of that feed into the probabilities of commuter vs. outsider.
The 91 is one of only a few logical routes to Las Vegas and “the River” from Orange County. “The River” refers to the Colorado River. There are several spots along it that are popular weekend getaways for those who enjoy drinking, wake boarding/ skiing, drinking, offf-roading, drinking, jet-skiing and drinking. For me, the 2nd best time to head out to Vegas/Havasu is Friday morning . Though there is morning traffic heading east, the morning commute going west is much tougher, jammed with commuters going to jobs in Orange County and returning home to more affordable housing east of OC. So while EB commuters are out there at 8 am, there is also a lot of Vegas and river traffic trying to get through the 91 before noon on Friday when the real traffic arrives.
I agree that two persons in the suspect vehicle isn’t the recipe for a successful secret.