Level 4 is steering wheel mandatory. Level 5 is steering wheel optional.
Geofencing is part of the criteria, but a car that can only drive in the USA but can’t drive in Europe still qualifies as level 5.
Similarly a car that refuses to drive in a blizzard but can do everything else is level 5. Being able to drive at night or moderate rain is mandatory however.
That said, there is plenty of slightly different definitions thrown about. I am sure someone is going to argue a car needs to be able to drive in any country to qualify etc etc.
Edit: To be clear existing self driving taxi services aren’t level 5 services with existing restrictions, but the car is physically capable of much more than it’s being used for. It can operate at night and in the rain etc they are however being extremely cautious.
Steering wheel doesn't matter, despite the cute mnemonic.
Level 4 cars need a steering wheel to be generally useful. But a limited vehicle like a taxi doesn't need a wheel, no matter whether it's 4 or 5.
I agree with the rest of what you said. Geofencing entire continents isn't about driving ability, and blizzards are an acceptable human-level restriction.
“For vehicles designed to be solely operated by an ADS, manually operated driving controls are logically unnecessary.29 To account for this, the NPRM proposed a regulatory scheme in which the affected standards would not assume that a vehicle will always have a driver’s seat, a steering wheel and accompanying steering column, or just one front outboard passenger seating position.”
They are apparently allowing level 4 Taxi to be considered full ADS even if they have additional “Stowed controls” options.
These levels come from the US’s National Highway Traffic Safety Administration formal definition in 2013. It’s been updated a few times since then with SAE introducing an extra level in 2014, but the point was really a formal definition for regulation.
No, that's what level 4 means. Level 3 can rely on having a driver to switch to, level 4 can't.
The difference between 4 and 5 is that 4 can park and give up under arbitrary circumstances, while 5 has to be able to keep going almost always.