1. A method comprising: determining, by one or more computing devices, an initial estimate for a location of an edge of a lane marker bounding a lane of a roadway; generating, by the one or more computing devices, a set of possible estimates for the location of the edge based on an offset distance and the initial estimate; selecting, by the one or more computing devices, a most likely estimate of the set of possible estimates based on sensor data collected for the roadway; and fitting, by the one or more computing devices, the sensor data to a model describing a location and shape of the edge.