  We study a single station two-stage reneging queue with Poisson arrivals,
exponential services, and two levels of exponential reneging behaviors,
extending the popular Erlang A model that assumes a constant reneging rate. We
derive approximate analytical formulas representing performance measures for
our two-stage queue following the Markov chain decomposition approach. Our
formulas not only give accurate results spanning the heavy-traffic to the
light-traffic regimes, but also provide insight into capacity decisions.
