I love filtering through traffic on my bike. My favorite hobby while passing cars trapped in traffic is counting how many aren't solo drivers in a given stretch of traffic, excluding work trucks/delivery. Usually it's under 10%. It's fun to imagine how this would look if all these people were on a bike, but 20' x 6' apart like they are currently arranged in these singly occupied cars. Bonkers.
I like your example... I've done the same, but it's important to remember that lots of those trapped people came from far away places on freeways that may not have access to a train... certainly that's true of the delivery trucks, which also couldn't deliver on a bicycle.
The key really is to move the marginal traffic that can switch. The key thing I see reducing cars is the absence of parking. Being at your destination, but unable to park (within a few blocks) is often enough to convince people not to drive.
