Cygan et al.'s planar linear arboricity conjecture

Let $G$ be a planar graph with maximum degree $\Delta\ge 5$. The linear arboricity ${\rm la}(G)$ is the minimum number of linear forests whose union is the edge set of $G$.

Planar Linear Arboricity Conjecture. For every planar graph $G$ of maximum degree $\Delta\ge 5$,

$${\rm la}(G)=\left\lceil \tfrac{\Delta}{2} \right\rceil.$$

The conjecture extends the known result for planar graphs of maximum degree at least $9$ and would imply the Vizing Planar Graph Conjecture for maximum degree at least $6$, which remains open only when $\Delta=6$.