This unpublished report describes a one-year study aimed at evaluating low-cost sensors in a dense network of near-road monitoring sites in the San Francisco Bay area. The overarching goal was to evaluate the ability of low-cost sensors to characterize traffic-related air pollution. The specific aims were to (1) colocate and compare low-cost sensors with regulatory instruments and (2) evaluate the ability of the low-cost sensors to characterize variations in traffic-related air pollution that are associated with different traffic counts. The topic of the study is of interest since the development and use of low-cost air pollution sensors are progressing rapidly, and these sensors have the potential to transform the way air pollution research is conducted.