The Federal Motor Carrier Safety Administration (FMCSA) Hazardous Material Routes were developed using the 2004 First Edition TIGER/Line files. The routes are described in the National Hazardous Material Route Registry (NMHRR). The on-line NMHRR linkage is http://hazmat.fmcsa.dot.gov/nhmrr/index.asp With the exception of 13 features that were not identified with the Tiger/Lines, Hazmat routes were created by extracting the TIGER/Line segments that corresponded to each individual route. Hazmat routes in the NTAD, are organized into 3 database files, hazmat.shp, hmroutes.dbf, and hmstcnty.dbf. Each record in each database represents a unique Tiger/Line segment. These Tiger/Line segments are grouped into routes identified as character strings in the ROUTE_ID field in the hmroutes.dbf table. The route name appearing in the ROUTE_ID is assigned by FMCSA and is unique for each State [this sentence could be deleted - it doesn't add a lot to it]. The hmstcnty.dbf table allows the user to select routes by State and County. A single shapefile, called hazmat.shp, represents geometry for all routes in the United States.
