I lived in the Phoenix area for over 40 years before moving to Florida last year. The accident occurred on I-10, 60 miles WEST of Phoenix. Tucson is 100 miles SOUTH of Phoenix. So your speculation is incorrect.
I-10 is a double lane divided interstate highway. How did a semi-tractor trailer cross the wide no-man’s-land median between the divided highways? There needs to be more details reported before we know who the occupants of the van were and how the accident actually occurred.
Vehicles cross the median on split interstate highways quite often. (Bad driving conditions, drivers falling asleep, etc)
Here in Iowa they’ve started erecting cable “catch” fences in the median. In just one year they have seen a dramatic reduction in fatalities.
Local coverage shows the tracks and other shots near the scene in the video segment.