  Features of a topological phase, and edge states in particular, may be
obscured by overlapping in energy with a trivial conduction band. The
topological nature of such a conductor, however, is revealed in its transport
properties, especially in the presence of disorder. In this work, we explore
the conductance behavior of such a system with disorder present, and contrast
it with the quantized conductance in an ideal 2D topological insulator. Our
analysis relies on numerics on a lattice system and analytics on a simple toy
model. Interestingly, we find that as disorder is increased from zero, the edge
conductivity initially falls from its quantized value; yet as disorder
continues to increase, the conductivity recovers, and saturates at a value
slightly below the quantized value of the clean system. We discuss how this
effect can be understood from the tendency of the bulk states to localize,
while the edge states remain delocalized.
