Central quotients of biautomatic groups

The quotient of a biautomatic group by a subgroup of the center is shown to be biautomatic. The main tool used is the Neumann-Shapiro triangulation of $S^{n-1}$, associated to a biautomatic structure on ${\Bbb Z}^n$. As an application, direct factors of biautomatic groups are shown to be biautomatic.