  We study a model of semi-flexible self-avoiding trails, where the lattice
paths are constrained to visit each lattice edge at most once, with
configurations weighted by the number of collisions, crossings and bends, on a
Husimi lattice built with squares. We find a rich phase diagram with five
phases: a non-polymerised phase (${\bf NP}$), low density (${\bf P1}$) and high
density (${\bf P2}$) polymerised phases, and, for sufficiently large stiffness,
two additional anisotropic (nematic) (${\bf AN1}$ and ${\bf AN2}$) polymerised
phases within the ${\bf P1}$ phase. Moreover, the {\bf AN1} phase which shows a
broken symmetry with a preferential direction, is separated from the ${\bf P1}$
phase by the other nematic ${\bf AN2}$ phase. Although this scenario is similar
to what was found in our previous calculation on the Bethe lattice, where the
${\bf AN-P1}$ transition was discontinuous and critical, the presence of the
additional nematic phase between them introduces a qualitative difference.
Other details of the phase diagram are that a line of tri-critical points may
separate the ${\bf P1}-{\bf P2}$ transition surface into a continuous and a
discontinuous portion, and that the same may happen at the ${\bf NP}-{\bf P1}$
transition surface, details of which depend on whether crossings are allowed or
forbidden. A critical end-point line is also found in the phase diagram.
