The paper deals with analytical and experimental study to determine the cause of transverse crack patterns on two parallel seven-span haunched steel-girder bridges. Major cracks are concentrated between the beginning and the middle of the third span. The crack patterns are symmetric with respect to the fourth span and can be found on both bridges. Diagnostic tests were performed with crawling-speed and high-speed trucks. The measured distribution factors are consistently more uniform than code-speciยฎed values and the impact factors are smaller than speciยฎed values. Tests on concrete cores indicated that the water/cement ratio is higher than code speciยฎed ratio and that the strength of concrete is greater than speciยฎed. Three-dimensional ยฎnite-element analysis indicated that stresses in the slab due to live load do not match with existing crack patterns. However, the analysis of the concrete pouring sequence showed that maximum concrete stresses are large and the locations correspond to those of the most severe slab cracking. Therefore, it is concluded that the bridge deck slab cracks resulted primarily from the deck pouring sequence, combined with concrete shrinkage. Since the primary causes of cracks are not active anymore, an epoxy injection method has been recommended to seal cracks.