Analysis: What's Up With the Title?
The first published version of this poem from the 1856 edition of Leaves of Grass was titled "Sun Down Poem." The imagery of light and darkness is central to the poem, but eventually Whitman must have decided that there was no reason to beat the reader over the head on this point. For the 1960 edition of Leaves of Grass, he revised the poem and changed its title to "Crossing Brooklyn Ferry," which is more helpful because it could be difficult for a reader who isn't familiar with the geography of New York to figure out in what direction the speaker is traveling. The poem was written several decades before the construction of the Brooklyn Bridge, connecting Manhattan and Brooklyn over the East River. To get from one side of the river to another, visitors and commuters had to take a ferryboat. We can assume that many of the passengers on the boat were on their way home from work.
You'll also notice that the title includes a gerund, "Crossing." The gerund tense creates a kind of eternal present tense that holds the reader within a particular moment in time. Whitman loved gerunds, and you'll find them all over his poems. We love them nowadays, too, in large part due to our influence from Whitman. Just think of the number of books and movies that have an "-ing" suffix in the title, from Finding Nemo to Becoming Jane to Reading Lolita in Tehran.