Learn Hardcore Russian: Для поездки требуется паспорт.

Поездки is in the genitive singular. The preposition для (“for”) always requires the genitive case, so поездка (nominative) becomes поездки (genitive) after для.

Why is паспорт in the nominative case rather than in the genitive?

In the impersonal construction with the verb требуется (“is required”), the thing that’s required stands in the nominative as if it were the subject. It is not governed by для, so паспорт remains in the nominative singular.

What part of speech is требуется, and how does this construction work?

Требуется is the 3rd-person singular form of the impersonal verb требоваться (“to be required”). There’s no explicit subject (“it”); instead, the verb describes the necessity of something (паспорт) and is often called a passive-impersonal construction.

Can I replace требуется with нужен? What’s the difference?

Yes. You can say Для поездки нужен паспорт. Both mean “A passport is needed for the trip.”

требуется is a bit more formal or bureaucratic.
нужен is more colloquial and direct.