  A practical autonomous driving system urges the need to reliably and
accurately detect vehicles and persons. In this report, we introduce a
state-of-the-art 2D object detection system for autonomous driving scenarios.
Specifically, we integrate both popular two-stage detector and one-stage
detector with anchor free fashion to yield a robust detection. Furthermore, we
train multiple expert models and design a greedy version of the auto ensemble
scheme that automatically merges detections from different models. Notably, our
overall detection system achieves 70.28 L2 mAP on the Waymo Open Dataset v1.2,
ranking the 2nd place in the 2D detection track of the Waymo Open Dataset
Challenges.
