Breakdown of Нам нужен автобус номер одиннадцать или двенадцать.
мы
we
автобус
bus
нужен
needed (short form)
или
or
Questions & Answers about Нам нужен автобус номер одиннадцать или двенадцать.
Why does the sentence start with Нам (to us) instead of Мы (we)?
This is because of the word нужен (is needed). In Russian, you don't literally say "We need a bus." Instead, the structure is "To us is needed a bus." The person who needs something takes the Dative case, so мы becomes нам.
Why is the word нужен used instead of нужно or нужна?
Нужен is a short adjective that has to match the gender of the thing that is needed. In this sentence, the thing needed is автобус (bus). Because автобус is a masculine noun, we use the masculine form нужен.
Why do we use the plain counting numbers одиннадцать and двенадцать here instead of "eleventh" or "twelfth"?
Just like in English, when identifying a specific bus route, flight, or room, Russian uses the word номер (number) followed by the basic counting numbers (cardinal numbers). You don't need to use ordinal numbers (like "eleventh").
Normally numbers change the ending of the noun they are attached to. Why doesn't автобус change here?