Aspects of the disclosure relate generally to detecting lane markers. More specifically, laser scan data may be collected by moving a laser along a roadway. The laser scan data may include data points describing the intensity and location information of objects within range of the laser. Each beam of the laser may be associated with a respective subset of data points. For a single beam, the subset of data points may be further divided into sections. For each section, the average intensity and standard deviation may be used to determine a threshold intensity. A set of lane marker data points may be generated by comparing the intensity of each data point to the threshold intensity for the section in which the data point appears and based on the elevation of the data point. This set may be stored for later use or otherwise made available for further processing.