Gigantic arms are not feasible because of how torque and leverage work.
As your arm gets longer, it has to get stronger, thus heavier, thus requiring larger motors, and anchored to the ground better. After a handful of meters, robot arms can’t hold themselves up, let alone carry a useful tool.
There are multiple meter long robot arms for lifting big things in factories but they are enormous, enormously expensive, and consume enormous power.
But here’s a delightful concept that sidesteps this, by making the arm weigh nothing:
This could simultaneously absolve the need for autonomous vehicles, because whenever you need to go somewhere, you could just make the giant arm put you there.
That's called a train. It's great. You can read a book while you are transported, it uses very little power to get you there, it can be 0 emission, there are no traffic jams. Sadly it's not fashionable cause you can't show off how wealthy you are by using it.
Why not both? You could have each train actually be an array of arms that reach out and pick people up and move them along their route. The arms wouldn't have to be as long since the train is moving along the rail, and a select number of arms could be reserved for first class passengers.
In the US, most tracks prioritize freight traffic over passenger rail. And there is a tremendous amount of freight traffic. There may not often be traffic jams, but when you are diverted to side track to wait and allow a priority freight train through, it's not uncommon to wait a very long time (I've been delayed more than an hour on the 3 hour train ride from Portland to Seattle).
There are also huge bottlenecks in US track infrastructure that absolutely do lead to traffic jams - perhaps most infamously in New York City. Vetoing the addition of 6 additional tracks through NYC is one of the reason Chris Christie was so hated.
It's faster than flights on short (<3 hour) routes because you don't have the whole security theatre thing. Also train stations are in the city center usually and airports are in the outskirts.
