The lines in the couplet "Streets coming fast/One after the other" contribute to the meaning of the poem by increasing the urgency and sense of movement, thereby speeding up the pacing of the poem. This quick succession of streets emphasizes the speaker's sense of distance and separation from their beloved, creating a feeling of inevitable loss as things rush past. Therefore, the correct answer is:
The lines in the couplet speed up the pacing of the poem.