3 to 5 on average
I think it’s a speech thing that got written down, but then also written as the number instead of the word.
Like they use of the word “one” like this:
That’s one weird thing to do.
That’s a weird thing to do.
So I read that as:
averages 3-5 passengers
averages a 3-5 passengers
averages one 3-5 passengers
averages 1 3-5 passengers
I can totally follow that logic. 1 and 3/5ths, rounding up to 2 for the next hypothesis. Very plausible explanation.