current capacity pcb trace
There are at least two aspects: Maximum current capacity of a trace respectively overtemperature and acceptable resistance respectively voltage drop. In low voltage circuits, the second is usually defining the trace widths.
I suggest to calculate the trace resistances. In your example it's already 8 mohm with a 1 oz (35 µm) copper PCB, quite a lot to my opinion.
As a another point, the melting integral ∫I²dt of the trace should be suficiently higher than of the fuse protecting the circuit.