|Mode of transportation||Percentage of Tons|
|Other and unknown modes||0.4|
NOTES: The total includes shipments via the air mode. However, an individual estimate for the air mode cannot be published because it does not meet the standard for release due to variability.
SOURCE: Research and Innovative Technology Administration and U.S. Census Bureau, 2007 Commodity Flow Survey, Hazardous Materials, Table 1c, available at http://www.bts.gov/publications/commodity_flow_survey/.