I'm not currently a bike commuter but I plan to be one soon. I have commuted a few times and it does involve single track through a NPS park.
Basically, I'll ride through neighborhoods two miles to the park, then ride 1-1/2 to 3 miles of single track (depending where I cut out). Then along a nice neighborhood road with a bike lane that dead ends at the park. That road dead ends into a really busy road with a bike lane. The bike lane eventually ends, less than two miles from work, and I'll take to the sidewalk. That leads to a very short new multiuse path that isn't quite finished yet but is close. Then a little more road and I'm at my office. Total ride is out 10 miles one way. I've got a CX bikes so since it is mostly road, that's what I'll ride. It's a huge contrast riding the single track compared to riding along the really busy road.
Without the single track, I'd have to ride a narrow, twisty road with a big hill and a good bit of traffic, no sidewalk I could jump on. On the way home, I probably will take advantage of the opportunity to ride more single track or at least the flat path along the river.