You can model waiting room arrivals same way you can model server load - using the Poisson Distribution<p><a href="http://en.wikipedia.org/wiki/Poisson_distribution" rel="nofollow">http://en.wikipedia.org/wiki/Poisson_distribution</a><p>As long as you can calculate the expected number of people that arrive you can adjust your operations to handle the worst case as you define it to be (ie, do we want to handle 70% within an hour? 90% within 2 hours?, etc.)