The conjecture that every 3-edge-connected graph has Frank number at most 3

Let $G$ be a $3$-edge-connected graph. Its Frank number $f(G)$ is the minimum number of orientations needed so that every edge is deletable in at least one of them. Frank-number conjecture. Every $3$-edge-connected graph $G$ satisfies

$$f(G)\leq 3.$$

The paper proves the general upper bound $f(G)\leq 7$, obtains $f(G)=3$ for the Petersen graph, and gives improved bounds for more restricted graph classes. Improving the general bound to $3$ remains open.