  We analyze Lorentzian spacetimes subject to curvature-dimension bounds using
the Bakry-\'Emery-Ricci tensor. We extend the Hawking-Penrose type singularity
theorem and the Lorentzian timelike splitting theorem to synthetic dimensions
$N\le 1$, including all negative synthetic dimensions. The rigidity of the
timelike splitting reduces to a warped product splitting when $N=1$. We also
extend the null splitting theorem of Lorentzian geometry, showing that it holds
under a null curvature-dimension bound on the Bakry-\'Emery-Ricci tensor for
all $N\in (-\infty, 2]\cup (n,\infty)$ and for the $N=\infty$ case as well,
with reduced rigidity if $N=2$. In consequence, the basic singularity and
splitting theorems of Lorentzian Bakry-\'Emery theory now cover all synthetic
dimensions for which such theorems are possible. The splitting theorems are
found always to exhibit reduced rigidity at the critical synthetic dimension.
