Piezoelectric energy harvesting from traffic load has gained extensive attention for potentiality as a renewable energy source. In existing in situ experiments, generally only one vehicle is employed, while the wheel-path of the vehicle and embedded positions of piezoelectric energy harvester (PEH) units are both fixed. However, in an actual traffic condition, vehicles travel randomly along width of pavements, which means the wheel-path varies over time and among vehicles. In this study, an electromechanical model is established for the PEH units under actual traffic conditions with wheel-path distribution, and is validated with finite element analysis and experiments. Then the electrical performance of PEH units embedded at various locations along pavements’ lateral direction is investigated under various traffic speeds. It is found that the optimal lateral embedded locations of the PEH units should be adjusted according to the prescribed traffic speed of the roads. Specifically, PEH units should be embedded at the tire-road contact areas for road with low traffic speeds (<15 m/s), while they should be embedded at the center of the pavement with high traffic speeds (>25 m/s). These mathematical results may serve as guidelines for selecting optimal lateral embedded locations for PEH units embedded in pavements.