Aspects of the disclosure relate generally to detecting the edges of lane lines. Specifically, a vehicle driving on a roadway may use a laser to collect data for the roadway. A computer may process the data received from the laser in order to extract the points which potentially reside on two lane lines defining a lane. The extracted points are used by the computer to determine a model of a left lane edge and a right lane edge for the lane. The model may be used to estimate a centerline between the two lane lines. All or some of the model and centerline estimates, may be used to maneuver a vehicle in real time and also to update or generate map information used to maneuver vehicles.