Learn Hardcore Japanese: kaisatu wo tooru mae ni yoyakukin wo harau hituyou ha arimasen. - You don’t need to pay a deposit before passing through the ticket gate.

In Japanese, some intransitive verbs that describe movement through or across a space still take を to mark the path or space being traversed. Examples include 通る (to go through), 走る (to run), 横切る (to cross). Here, 改札を通る literally means “to pass through the ticket gate.”

How does the phrase 通る前に work? Why is 前 placed after 通る rather than after 改札?

The pattern [Verb-plain form] + 前に means “before doing [verb].” You attach 前に directly to the verb that describes the action you want to refer to.
• 改札を通る前に = “before passing through the ticket gate.”
If you instead said 改札の前に, that would mean “in front of the ticket gate” (i.e. the location).

What is the structure of 払う必要はありません, and how does it link back to 通る前に?

払う必要はありません literally breaks down as:

払う – verb in dictionary form (“to pay”)
必要 – noun meaning “need” or “necessity”
はありません – negative polite form of “to exist” (here: “there is no …”)

Together, 払う必要はありません means “there is no need to pay.” Because it follows 通る前に, the full sentence reads:
“Before passing through the ticket gate, there is no need to pay the reservation deposit.”

Why do we use はありません instead of がない with ?