What target heart rate or power do people use when commuting by bike
I would claim, without data so just thinking about my experience with the world, that most commuters are not targeting heart rate or power, they are just trying to get to work.  Some want to get there as fast as they are (reasonably) capable of and some are wanting to get there at a reasonable pace that does not require a shower. Many just want to get there.  There must be some who try to combine sophisticated training with commuting, but those are few.