There are several information's that are already given in the question. Based on those given information's, the answer can be easily deduced.
w = 0.92
Then
w(x)=x^2/2(1-x)
w(0.92) = (0.92)^2/2(1 - 0.92)
= 0.8464/0.16
= 5.29
From the above deduction, it can be concluded that the average number of vehicles waiting is 5.29.