Since it's a commute, we tend to also want our speeds to be reasonable. Getting there in less time encourages us to cycle there more often. Even if you live close to work, a round trip can make the recovery ride long enough for a workout done the day before. A commuter might decide to go briefly outside the recovery zone briefly to avoid missing green lights. A few seconds earlier can save you up to two minutes!
If we do 30 seconds all out, it would be HIIT even though it's brief. Doing HIIT everyday can cause overtraining. Interestingly, 100m sprinters are able to do many reps a day and not overtrain, making it important to draw the line. Pushing too hard makes it no longer active recovery. http://sftrackandfield.com/track-workouts/
What I know is that even though must of the time is spent in recovery zone during intervals, doing it everyday is likely too much.
What intensity levels or heart rate can we do and for how long and still count as a recovery day?
How long can I sprint to make that light? The light might expire in 5 to 10 seconds. Some traffic lights have shorter cycles, can be activated by pedestrians or cyclists, don't display how much time is left, or their lights are obstructed, making them less predictable.
In another example, let's say there's 20 seconds left for the green light and it may be missed by 5 to 10 seconds at an easy pace. Can I ride at the VO2 max zone for up to 20 seconds to make it? The VO2 max zone is more than twice the power of that of the recovery zone. If not, should I ride at the threshold zone which is only about up to 20% less than the VO2 max zone to make it instead?