The increasing progress of transportation systems has led to a drastic increase in the demand for smart systems to monitor traffic and street safety. One important information for such systems is the locations and number of specific types of vehicles, and it is goal of this Challenge to provide a comprehensive performance evaluation to state-of-the-art detection and counting algorithms. The challenge is based on the UA-DETRAC dataset, a real-world multi-object detection and multi-object tracking benchmark. The dataset is composed of traffic video sequences annotated with vehicle bounding boxes and trajectories at various challenging levels. The UA-DETRAC challenge will be held in conjunction with the International Workshop on Traffic and Street Surveillance for Safety and Security (T4S), and works with performance over the baseline thresholds are encouraged to be submitted and peer reviewed for acceptance.