You don't enter or exit at 120kph so throughput is cut by the bottle neck of exiting/entering (also the reason why there's traffic no matter the number of lanes, bottleneck is the throughput of entry exit creates the traffic stall

I gotta take issue with those numbers. A car moving at 130kph covers 18 meters in about half a second. According to the numbers I found online, experts estimate the perception-reaction time for braking at 1.5 seconds, which is up from the value of 0.75 seconds that they used to use. Thirteen and a half meters is an unrealistically-close following distance, even for German super-humans.

I have not driven on the Autobahn, but the videos I can find show scenes much more consistent with a ~55 meter (1.5 seconds) gap between cars, or much-slower traffic speeds. That drops the estimated human-throughput way, way down.

Here is some data to get more accurate numbers:

• max speed on that highway for cars is 80km/h
• the bicycles had an average speed of ~18km/h

Ok, but still healthier for all.

And you can savely take half of car throughput on average. Or far less in congestion.