Risky steering operations are detected based on the relationship between the radius of road curvature and road design speed defined in the road construction ordinance. Vehicle motion while steering is approximated as a circular motion, and the vehicle trajectory radius is estimated from lateral acceleration and vehicle velocity captured with a drive recorder based on a circular motion equation. Steering operation behaviors are evaluated for 203 drivers. Experimental results show that the percentages of risky steering operations estimated for individual drivers correlate with driver risk evaluation scores given by a risk consulting expert. We also observed situations of risky steering by recording video along with driving data using a data collection vehicle.