I am trying to import the National Bridge Inventory Lat/Long data into ArcGIS. But when I do it with WGS 1984 Geographic coordinate system, they don't match with the base maps. I don't where I am going wrong. To convert the Lat/Long values I am using the ddMMSSHH concept.
At the top of the page linked to in the comment and now question is a line "Recording and Coding Guide for the Structure Inventory and Appraisal of the Nations Bridges" with a pdf and doc format link. This document includes the metadata for each field in the data, and it confirms mkennedy's interpretation that it's (D)DDMMSS.ss and assumes positive west longitudes (the specified format doesn't allow for signs). They don't, however, specify a datum reference though they do mention 'for GPS use'. The original WGS84 and NAD83 are extremely similar for North America, depending on your accuracy requirements.