Systems and methods for estimating lane geometry are disclosed herein. One embodiment receives sensor data from one or more sensors; detects a road agent based on the sensor data; detects, based on the sensor data, that the road agent has performed a lane shift from a first lane of a roadway to a second lane of the roadway; and estimates a boundary line between the first lane of the roadway and the second lane of the roadway based, at least in part, on the detected lane shift.