Other mistake: When Sue Ellen gets the roses from Gus, the tickets in the card have a date of April 6th 1990. This is suppose to be the summer of 1990, which means the tickets are no good. (01:03:00)
Other mistake: The movie is set in the summer of 1990 and Sue Ellen has stated she is 17 but when we see her drivers license her birthdate is stated as 12-19-73. That makes her 16 turning 17 in December. (01:24:00)
Answer: People in LA commute in all sorts of directions for work. And the freeway you see is the 405 in West LA (not the "city" - or Downtown where she worked). This freeway would not even be her direct route anyway. All just made up in the film.