  We study BV solutions for a $2\times2$ system of hyperbolic balance laws. We
show that when initial data have small total variation on $(-\infty,\infty)$
and small amplitude, and decay sufficiently fast to a constant equilibrium
state as $|x|\rightarrow\infty$, a Cauchy problem (with generic data) has a
unique admissible BV solution defined globally in time. Here the solution is
admissible in the sense that its shock waves satisfy the Lax entropy condition.
We also study asymptotic behavior of solutions. In particular, we obtain a time
decay rate for the total variation of the solution, and a convergence rate of
the solution to its time asymptotic solution. Our system is a modification of a
Keller-Segel type chemotaxis model. Its flux function possesses new features
when comparing to the well-known model of Euler equations with damping. This
may help to shed light on how to extend the study to a general system of
hyperbolic balance laws in the future.
