I wonder how much is just that; "feeling". I'm reminded of the gorilla suit attention test, which shows the brain's ability to filter out extraneous stuff when it focuses on a task.

I think it's possible that going faster simply requires more focus, so that your brain is simply filtering out those close car shaves. Alternatively, when you are toodling along at a speed that requires no attention at all to cadence or breathing, and less attention to your line of travel, you won't focus so much, so that more extraneous information makes it's way to your attention.