US Hazardous Materials Routes

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.

In order for the public to be able to view the Hazardous Material Routes reported to FMCSA, the data is being released in ESRI shapefile format for use in a GIS system.

The data provided is in the native Latitude/Longitude coordinate
system inherited from the TIGER/Line data.

Accuracy is inherited from the TIGER/Line files:
The Census Bureau uses Global Positioning System (GPS) coordinates at road centerline intersections to evaluate the horizontal spatial accuracy of source files that may be used to realign road features in the TIGER database and test the horizontal spatial accuracy of the road features in the TIGER/Line files.  The test compares a survey-grade GPS coordinate to its associated road centerline intersection in the TIGER file.  The test is based upon an independent collection of GPS coordinates for a random sample of road intersections from a centerline file that meet certain criteria. The points are referred to as the sample points and are gathered through a private contractor working for the Census Bureau.  Since
the collection method uses survey-quality GPS-based field techniques, the resulting control points are considered "ground truth" against which the TIGER road centerline intersection coordinates are compared. The distances between the coordinates are calculated and the Census Bureau determines the Circular Error 95% (CE95).  That is, the accuracy of the file in meters with 95% confidence.  The CE95 can be calculated from the mean and standard deviation by using the formula: mean of differences plus (2.65 times the standard deviation). CE95 results reported for each file tested are determined using a spreadsheet with embedded statistical formula.  The use and applicability of the spreadsheet and its embedded formula have been verified by Census Bureau statisticians.  The basis of the calculation is the use of the root mean square error (RSME).  This is the method as stated in the U.S. Government's Federal Geographic Data Committee
Standard FGDC-STD-007.3-1998, Geospatial Positioning Accuracy Standards.
Part 3: National Standard for Spatial Data Accuracy.  The results of using this measure of accuracy are in compliance with Federal Spatial Data requirements.
In terms of the Census Bureau application, the dataset coordinate values
are those taken from the centerline file and the coordinate values from
an independent source of higher accuracy are those acquired through the
Census Bureau's contractor. Refer to the 2004 First Edition TIGER/Line metadata for each county or statistically equivalent entity for information on the spatial accuracy of features in that county. Please note that the horizontal spatial
accuracy, where reported, refers only to the realigned road features identified as matched to the positionally accurate source file with that accuracy.  It is not the spatial accuracy of the TIGER/Line file as a whole.