For me when I decide to take a structured workout outdoors I tend to focus on the purpose of the workout and not the exact power and time of each interval. I do this so I don’t drive myself nuts during the ride. Typically I will write out the intervals with time and a power range on a sticky note then tape that to my stem. Then I have a profile and page on my Garmin that turns off auto lap and the page will show my lap power, 3 sec and 30 sec power, and Lap Time.
So for today I have Ebbetts scheduled which is 4 x 8 min at 88-94% intervals with 4 burst during each interval, if I did that outdoors I would have "4 x 8min (280-310) w/ 4 Bursts Rest 4min " on my sheet. I typically don’t focus too much on the warm-up or cooldown time just go off feel for that. Now when after I am done with my warm-up once I have a good spot for an 8 minute interval I’ll hit lap and try to keep my Lap Power avg and 30 sec avg in that power range and fit in those 4 bursts where appropriate. Once I get near the 8 min mark I’ll be prepped to hit the lap at 8 min or when I am at a point I may have to drop power (descent or stop), then I’ll ride easy until 4 minutes or when it is a good time for the next 8 minute interval.
This is by no means an exact match of that workout, but as long as I don’t do anything crazy during the workout I would think I achieved the purpose of the workout. I really haven’t found a workout I can’t at least get the intervals around 90% imitated. Over/under’s are great with a partner as you can trade off pulls to both simulate race conditions and the workout. The only workout I wouldn’t do outdoors is something anaerobic with super tough intervals that put you in a hole and that is only because the danger of spacing out on an open road. I also am fortunate I live where there are tons of country roads I can ride to from my house that have very little car traffic.