This is the 5020th most frequent Russian word.
магистралей
"Магистралей" translates to "highways" or "main roads" in English.
Магистралей is used here to describe the vicinity and features along major roads.
Вдоль магистралей расположены заправки и кафе.
Along the highways, there are gas stations and cafes.
Магистралей in this genitive plural question form indicates comparison and identification of major roads.
Знаете ли вы, какие магистралей являются самыми загруженными в городе?
Do you know which highways are the busiest in the city?
Магистралей is used here in the genitive plural form referring to major roads or highways.