People ignore speed limits. You design the street to feel best at the speed you want people to go.
One of the States, I think Maine? Took a road and adjusted the posted speed limit at various points spanning like 20 mph differences, and at all posted speeds the average actual traffic speed was still the same. Because that speed felt right for that road to most drivers, regardless of what was legal.
If there are good alternative options for public transport, then the slower speed limits and roads designed to slow traffic will gradually shift people to use those options instead.
I've been preparing for this my whole life, plenty of food preparation for hibernation.