The objective of this study was to assess the magnitude of overheight vehicle collisions with highway bridges that caused structural damage, injuries, and sometimes even fatalities at both the Maryland and the national levels. The seriousness of the collisions was exemplified by a case in 1999 in which a truck hauling an overheight excavator struck and collapsed a pedestrian bridge over the Baltimore Beltway, killing one motorist and injuring three others. Statistics on overheight collisions in Maryland were collected from overheight vehicle detector records, the statewide accident database, and bridge inspection reports. An analysis of the data revealed that the frequency of overheight accidents reported in Maryland increased by 81% between 1995 and 2000. Of the 1,496 bridges susceptible to impact by overheight vehicles statewide, 309 (20%) have been struck, with 58 (4%) having required repairs. No nationwide databases on overheight collisions exist, so a survey was sent to each state to collect national statistics. Of the 29 states responding, 18 (62%) indicated that they consider overheight collisions to be a significant problem, but few were able to provide hard data.