Multi-stage vehicle detection systems and methods for side-by-side drive-thru configurations. One or more video cameras (or an image-capturing unit) can be employed for capturing video of a drive-thru of interest in a monitored area. A group of modules can be provided, which define multiple virtual detection loops in the video and sequentially perform classification with respect to each virtual detection loops among the 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.