Why is there a line of parked cars at the left of the general lane in Otay Mesa Port of Entry?

I saw a line of parked cars in the general lane in Otay Mesa Port of Entry (from Mexico to the US) in early January at night (ca. 4 am). The left lane in the following picture shows the parked car:
That surprises me as at that stage of the queue I think (perhaps erroneously) that one has to cross the border, and therefore I don't see why one would park there.
Why is there a line of parked cars at the left of the general lane in Otay Mesa Port of Entry?
I did see a few people sleeping in some of them: is it a queue of people waiting for some visa/access permits to the US? Or getting a head start on the queue when they wake up to go to work to the US in the morning (in which case why not find a quieter spot to sleep in the US)?
Pictures about "Why is there a line of parked cars at the left of the general lane in Otay Mesa Port of Entry?"



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Images: Ibrahim Boran, Spencer Davis, Erik Mclean, Erik Mclean