A train isn’t affected by people randomly braking or weaving around different lanes because they lack driving skill. A train also isn’t as affected by inclement weather.
There is the classic set of pictures showing how much space is needed to transport 60 people by bus, by bike, and by car.
https://humantransit.org/2012/09/the-photo-that-explains-alm...
On my (pre-covid) morning commute to the office, most of the cars crawling along the highway had one person in them. The slowness is the result of people trying to merge into the highway, not "bad drivers".
Another way to illustrate how much space cars take up is to look at suburban office parks. There will be a small building (usually 1 or 2 stories) surrounded and dwarfed by a parking lot.
https://usa.streetsblog.org/wp-content/uploads/sites/6/2014/...
https://www.google.com/maps/place/Liberty+Lake,+WA/@47.67315...
I stand by my point on "bad drivers". It's a well-studied phenomenon[0] and it's not a matter of opinion.
According to a 2005 report for the Federal Highway Administration, the leading cause of congestion is bottlenecked infrastructure.
https://en.wikipedia.org/wiki/Traffic_congestion#Causes
I used to drive 405 North into Bellevue, WA. In the space of 3 miles, 3 highways merged into 405 North. There was always a traffic jam, every morning. It started at roughly the same spot every morning. It cleared up at roughly the same spot every morning. That was slow traffic caused by the infrastructure.
If the drivers staying in the far right lane didn't do that mindlessly (their exit is not next or soon, why are they there?) or if they actually kept space open ahead of them for the cars they can see are about to merge, these problems would largely evaporate.
I'm paraphrasing poorly but, "do things slowly so that they go smoothly. Things done smoothly go fast."