Weigh-in-motion sensor (200) comprising a beam (104) with a load-bearing top surface (110), and including a base wall (208) and a cover (210) with a cavity (116) therebetween. A sensing package (106) is disposed within the cavity (116) and is under pre-load between the cover (210) and the base wall (208). The sensing package (106) comprises a piezoelectric element (228) disposed in a guide (238) and interposed between an upper or first electrode (224) and a lower or second electrode (226). Insulators (244, 246) are interposed between the respective electrodes (224, 226) and the cover (210) and the base wall (208). An aperture (248) is formed within the base wall (208) and a fastener (244) is disposed in the aperture (248) and in contact with a substrate (229) to impose a preload on the sensing package (106). The fastener (244) has a diameter (D1) which is larger than a transverse dimension (D2) of the piezoelectric element (228) (e.g., about 10 percent larger) to provide an improved degree of beam stress reduction without sacrificing sensor measurement sensitivity.