A 4.5 degree grade is actually a 7.59% grade, REALLY STEEP!
For continuous running should be 1 1/2% to 2 1/2% grade (1 1/2 inch rise in 100 inches, etc.).
For a line to a storage area up to 4% would work but with speed restrictions and good visibility.
Also side to side track protection would also be in order! Russ