1. A multi-stage vehicle detection system for side-by-side drive-thru configurations, said system comprising: at least one video camera for capturing video of a drive-thru of interest in a monitored area; and a plurality of modules that defines multiple virtual detection loops in said video and sequentially performs classification with respect to each virtual detection loop among said multiple virtual detection loops, starting from a virtual detection loop closest to an order point, and when a vehicle having a car ID is sitting in a drive-thru queue, so as to improve vehicle detection performance in automated post-merge sequencing.