  The generalized harmonic representation of Einstein's equation is manifestly
hyperbolic for a large class of gauge conditions. Unfortunately most of the
useful gauges developed over the past several decades by the numerical
relativity community are incompatible with the hyperbolicity of the equations
in this form. This paper presents a new method of imposing gauge conditions
that preserves hyperbolicity for a much wider class of conditions, including as
special cases many of the standard ones used in numerical relativity: e.g.,
K-freezing, Gamma-freezing, Bona-Masso slicing, conformal Gamma-drivers, etc.
Analytical and numerical results are presented which test the stability and the
effectiveness of this new gauge driver evolution system.
