Austin has an internal system. The key is to get the externally sourced materials as close as possible to where you need them on the assembly line. When you make big, fat manufacturing buildings it's hard to get all the material (raw or finished goods) to where they need to be if you unload only at the perimeter. Hence an internal delivery system 'tricks' the factory into thinking it's thinner than it really is.
I need that same system to trick my body into being thinner than it is...
If I may add to this.
1) Putting the part on the car is the only value added assembly step.
2) Shuttling parts out of trucks and into storage locations and out of storage locations (with dynamic locations, no-less) and then to the assembly lines involves sizable investment of all sorts - before you even put the part on the car!
3) If the robot that is putting the part on the car can pull it off of the truck directly, huge investments can be avoided.
There is also an entire industry dedicated to feeding and orienting parts so that a robot can pick them up. Or using sophisticated 3D vision to get a robot to pick a part out of a bunch of randomly oriented parts delivered in a bushel basket.
The part being made in the supplier's factory is not made in random orientation. It is made in a specific orientation. If you can maintain that orientation through the transportation/delivery process the orientation problem comes pre-solved. Robot picks the part off a tray and puts it on the car.
Trucks start to look like beer trucks with side access. You do a lot of work specifying exactly how you want things delivered, and ask your suppliers to preserve orientation rather than play 52 card pick up every time they ship you something, but you end up way ahead.
If the trucks are electric, you can drive/index them through an enclosed space.
The speed, quality and cost of this approach is twice as good. [Just count the number of times you do not move a part. 2 or 3 to 1 less motion.]
This shows up as fundamentally lower COGS which gives the business room to maneuver. Can lower price to take share at will. Nobody else can follow. It lets you write your own ticket.