AbstractIn this paper, we propose a lane change decision scheme using only commercial, automotive radar sensors with “DRiving Environment Assessment and decision Making (DREAM) index.” First, the index associated with a risk situation is assessed by the concept of a dynamic occupancy grid zone. The predefined distance of the local area was set to conform to the international standard of a steering function. Also, the risk assessment was predictively conducted using modeling of the relative motion with a target vehicle. Second, the index associated with a cooperative driving concept of the surrounding vehicles is proposed. To estimate the relative acceleration which is not directly measured by radar, we designed a discrete‐time state estimator. We executed scenario‐based experiments with test vehicles in a high‐speed circuit to validate the decision scheme. Through the experiments, we observed that the DREAM index could make effective decisions, and the lane change maneuverings were performed successfully in real‐world tests.