You ever see a dog that’s got its leash tangled the long way round a table leg, and it just cannot grasp what the problem is or how to fix it? It can see all the components laid out in front of it, but it’s never going to make the connection.
Obviously some dog breeds are smarter than others, ditto individual dogs - but you get the concept.
Is there an equivalent for humans? What ridiculously simple concept would have aliens facetentacling as they see us stumble around and utterly fail to reason about it?
Based on a game* I think that the root issue is that there are multiple bottlenecks, unavoidable for the drivers, like turning or entering/leaving lanes, forcing them to slow down to avoid crashing. Not a biggie if there are only a few cars, as they’ll be distant enough from each other to allow one to slow down a bit without the following needing to do the same; but once the road is close to the carrying capacity, that has a chain effect:
There are solutions for that, such as building some structure to handle those bottlenecks, but they’re often spacious and space is precious in a city. Or alternatively you reduce the amount of cars by discouraging people from using them willy-nilly, with a good mass transport system and making cities not so shitty for pedestrians.
*The game in question is OpenTTD. This is easy to test with trains: create some big transport route with multiple trains per rail, then keep adding trains to that route, while watching the time that they take to go from the start to the end. The time will stay roughly constant up to a certain point (the carrying capacity), then each train makes all the others move slower.
Laughs in good public transit(rail based is based, but buses are good too), where it can achieve 10~100x the capacity in the same footprint
With rail, as long as you have a good timetable and a robust signaling system, 27tpdph with multiple service patterns is achievable, and >33tpdph if you run just one service pattern, all while having a top speed of 120km/h and an average speed of >50km/h
Railway in general (excluding Line-of-sight based light rail and trams) can move stupendous amounts of people at full speed really quickly due to signaling and mass transit inherently being more efficient in general
Most of the time and places a city doesn’t need that capacity. Since your rail cannot get the garbage from my house, or my new bed to the house, we need roads as well. Thus for most a bus running in mixed traffic (remember most roads do not have heavy traffic!) is good enough and a lot cheaper. Where you need capacity a train is really good, but you don’t need it.
That said I support trains in a lot more places because trains can run fully automated and thus in the real world can achieve the high frequency people need to choose transit even when a car isn’t a problem to own (they can afford it and there is no traffic). This is however just a stop gap since self driving buses don’t exist (yet?). In most “first world” countries cost of labor is high and automated trains are thus useful in places where a bus could do the job.