I have to practice on that "it's not a race" part. Prior to this commute, I had exactly 3 rides on the road, mainly to test out parts of the commute. In all three, I went hard and found that I had to really work to slow down to maintain a reasonable pace.
I wore a HRM on my commute home and my aveHR was 173 with about 50% over 180 (and my running maxHR is 202). Obviously, I was pushing too hard.