Here, a speaker watches someone they love spiral and feels completely powerless. The driving image carries the whole poem: "you" is going too fast, and the speaker admits "i do not think / that i can catch you." The wishes pile up, each one more desperate than the last. Slow you down, grab the keys, scream at the other drivers. Each is a way of reaching in, and each is quickly given up as impossible.
The last line shifts the scene inward. The "side streets of your mind" suggest the danger isn't really on a road at all. It's in the person's thoughts, which seem to race and blur. The poem doesn't say exactly what is wrong, so the reader has to infer it, perhaps distress or a mind moving faster than anyone can follow.
The mood is anxious and helpless, with a hint of tenderness. The lack of punctuation and the single run-on sentence give it a breathless, rushing feel, as if the speaker is panicking in real time.