That's a tough one. To avoid overheating during the trip, you should feel cold initially. But if you start with a low intensity part, it'll be difficult to warm up. And if you wear enough for the downhill, you'll be soaking wet during and after the uphill part.
I'd wear something windproof that has ventilation zippers, or remove the shell after descending before tackling the uphill part.
When you arrive to the bus stop/station, reduce clothing before locking up your bike, so you'll cool down before entering the bus.
and I've been pairing it with an Arcteryx Atom LT jacket but that may be overkill for temps above freezing. I may try my lightweight rain jacket initially as the extra layer. Granted it doesn't breath well, but the ride isn't long enough for me to get sweaty while on the bike.
I like the ideas of a zipper/Velcro front that you can close during the downhill and open for the climb. Also like the recommendation to remove the jacket as soon as you get to the bus stop to start cooling down.
Additional things I'd do. Baggy sleeves. keep em closed tight on the down hill, but open them up for the climb. Unless you're wearing a backpack, it'll cause a little airflow along your arms and back to help keep things cool. I'd also add some distance to the start of the commute with a little bit of climbing to warm you up before the downhill.
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