Posts that are people just losing their mind over an interface change is what is ridiculous. Just because you don't know what you are doing doesn't make the new way any worse than the old one. How simple can this be?
Click the Add button (just like before)
Choose from the list of allowed items (just like before)
Drag slider to desired amount.
Done - car is now full. If you want the load copied to other like cars hit the icon for that on the right - CAKE.
if you want to add more available commodities to this car or others just add to what this car can support. This can also be copied to like cars.
This isn't really all that different than the "old" way except that you can adjust the levels with a slider. The real drawback to this new way is that it doesn't show multiple queues very well but its certainly not unusable

.