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Chapter 6 Safety, Energy, and Environmental Implications of Freight Transportation

Growing demand for freight transportation heightens concerns about its safety, energy consumption, and environmental impacts.  While safety in all freight modes continues to be monitored actively, the availability of energy consumption data has declined with the discontinuation of the Vehicle Inventory and Use Survey.


While the amount of freight transportation activity has increased, the total number of freight related transportation fatalities declined by 30.2 percent from 1990 to 2013. The truck, rail, and waterborne freight modes substantially reduced fatalities over that period. Large trucks accounted for 88.0 percent of all freight transportation fatalities. The vast majority of truck- related highway fatalities involved passenger vehicles.

Table 6-1. Fatalities by Freight Transportation Mode:  1990, 2000, and 2010-2013

Figure 6-1. Fatality Rates for Select Transportation Modes:  1990-2013

From 1990 through 2013, the overall rate of highway fatalities per vehicle-miles of travel (vmt) declined by 47.4 percent as the highway modes, except for motorcycles, showed across-the- board reductions. Fatalities per vmt for large-truck occupants decreased by 47.9 percent.

Table 6-2. Injuries by Freight Transportation Mode:  1990, 2000, and 2010-2013

Large trucks have accounted for nearly all (95.8 percent) freight transportation-related injuries, but the number of injuries has dropped by 41.8 percent since 1990.

Table 6-3. Hazardous Materials Transportation Incidents:  1990, 2000, 2010-2014

Because most hazardous materials are transported by truck, the majority of incidents related to the movement of hazardous materials occur on highways or in truck terminals. A very small share of hazardous materials transportation incidents are the result of a vehicular crash or derailment (referred to as “accident related”). Approximately 2.0 percent of incidents were accident related in 2014, but they accounted for 80.9 percent of all property damage. Most hazardous materials incidents occur because of human error or package failure, particularly during loading and unloading.

Table 6-4a. Commercial Motor Carrier Compliance Reviews by Safety Rating:  2013 and 2014

Federal and state governments conducted 7,666 safety compliance reviews that resulted in a formal safety rating in 2014. Of that total, only about 5.7 percent of motor carriers received an unsatisfactory rating.

Table 6-4b. Commercial Motor Carrier Compliance Reviews by Type:  2011-2014

Federal and state governments also conduct shipper, cargo tank facility, and onsite comprehensive safety analysis reviews.  More than 14,900 reviews were conducted in 2014.

Table 6-5. Roadside Safety Inspection Activity Summary by Inspection Type:  2000, 2010, 2013, and 2014

About one-fifth of all roadside inspections of commercial vehicles resulted in a vehicle being placed out of service (OOS) for a serious violation. A lower share of driver and hazardous materials inspections resulted in OOS orders. In 2014, 5.0 percent of driver inspections and 4.0 percent of hazardous materials inspections resulted in an OOS orders.


From 2007 to 2013, increases in fuel costs, a slight decrease in the number of trucks on the road, and improved energy efficiency affected the number of gallons of fuel burned by commercial trucks. Truck fuel consumption declined by 8.3 percent, from 47.2 to 43.3 billion gallons. Fuel use in Class I freight railroads declined by 9.2 percent, from 4.1 billion gallons in 2007 to 3.7 billion gallons in 2013.

Table 6-6. Fuel Consumption by Transportation Mode:  2007, 2009, and 2011-2013

Table 6-7. Energy Consumption by Select Freight Transportation Mode:  2007, 2009, and 2011-2013

In 2013, trucking accounted for a large majority of freight transportation energy consumption, followed by water, a distant second.

Table 6-8. Single-Unit Truck Fuel Consumption and Travel:  2007-2013

Miles per gallon for single-unit trucks (based on total travel and fuel consumption) remained relatively stable over the 2007 to 2013 period. From 2007 through 2012, single-unit trucks traveled fewer miles overall and averaged fewer miles per vehicle, resulting in reduced fuel consumption. In 2013, these trends were reversed as single-unit trucks traveled more miles overall and more miles per vehicle than the previous year, resulting in more fuel consumed.

Table 6-9. Combination Truck Fuel Consumption and Travel:  2007-2013

Miles per gallon for combination trucks (based on total travel and fuel consumption) also declined slightly between 2007 and 2013. From 2007 through 2012, vehicle-miles traveled by combination trucks declined by about 20.6 billion (about 11.2 percent). In 2013, this trend was reversed as combination trucks traveled more miles overall than the previous year, resulting in more fuel consumed.

Table 6-10. Energy Intensities of Domestic Freight Transportation Modes:  2007-2013

Energy intensity is the amount of energy used to produce a given level of output or activity, in this case vehicle-miles and ton-miles. In recent years the energy intensity of trucking has remained relatively stable, while rail and water have improved slightly.


Air quality is affected by vehicle emissions. Compared with gasoline-fueled cars and trucks, diesel-fueled heavy trucks emit small amounts of carbon monoxide (CO) but larger amounts nitrogen oxides (NOx). However, since 2000 the rate of NOx emission from diesel-fueled heavy-duty trucks declined by 63.1 percent.

Table 6-11. Estimated National Average Vehicle Emissions Rates of Heavy-Duty and Light-Duty Vehicles:  2000, 2010, 2014, and 2015

Table 6-12. Freight Nitrogen Oxides (NOx) and Particulate Matter (PM-10) Emissions by Single-Unit and Combination Trucks:  2000, 2010, 2015, 2020, and 2030

Trucks are the largest contributor to freight emissions nationally. The U.S. Environmental Protection Agency estimates that trucks will produce nearly 2.4 million tons of NOx in 2015. Substantial reductions in freight-related NOx emissions have been made since the U.S. Environmental Protection Agency required the use of ultra-low sulfur diesel fuel in heavy-duty trucks and other diesel-powered highway vehicles beginning in 2006.  Between 2000 and 2015, NOx emissions from single-unit and combination trucks decreased by 61.7 percent.  PM-10 emissions declined by 66.5 percent over the same period.  Truck-related NOx and PM-10 emissions are projected to further decline by 87.5 percent and 49.6 percent, respectively, from 2015 to 2030.

Table 6-13. U.S. Greenhouse Gas Emissions by Economic End-Use Sector:  1990, 2005, and 2010-2013

In addition to CO, NOx, and particulate matter emissions, the transportation sector releases large quantities of greenhouse gases (GHGs), such as carbon dioxide (CO2), methane, nitrous oxide, and hydrofluorocarbons.  When emissions from electricity are distributed among end-use sectors, transportation is responsible for about 27 percent of all greenhouse gases emitted in the United States in 2013.  The industrial sector produces the largest amount of GHG emissions (28.8 percent). 

Table 6-14. U.S. Transportation Sector CO2 Emissions from Fossil Fuel Combustion by Fuel Type:  1990, 2005, and 2010-2013

Carbon dioxide accounts for nearly all of the transportation sector’s GHG emissions, primarily from the combustion of fossil fuels. Almost all of the energy consumed by the sector is petroleum-based and includes motor gasoline, diesel fuel, jet fuel, and residual oil.  Gasoline-fueled passenger cars and light-duty trucks are responsible for about 59.7 percent of transportation sector CO2 emissions while the combustion of diesel fuel in medium- and heavy-duty trucks and jet fuel in aircraft produced much of the rest. 

From 1990 to 2013, transportation sector CO2 emissions as a percent of the U.S. total was between 31.5 and 33.3 percent

Table 6-15.  U.S. Greenhouse Gas Emissions from Domestic Freight Transportation:  1990, 2005, and 2010-2013

Since 1990, the rate of growth of greenhouse gas emissions from freight sources has been more than six times as fast as that for passenger travel. Trucking accounted for 77.1 percent of freight emissions followed by freight rail, a distant second. 

Table 6-16. Medium- and Heavy-Duty Truck Greenhouse Gas Emissions:  1990, 2005, and 2010-2013

Between 1990 and 2013, medium- and heavy-duty truck emissions rose by 76.4 percent, the largest percentage increase of any major transportation mode.   An increase in truck freight movement is largely responsible for the rise in emissions over the last two decades.

Table 6-17. Number and Volume of Oil Spills In and Around U.S. Waterways:  1990, 2000, and 2012-2014

Water quality is affected by oil spills from vessels and pipelines transporting crude oil and petroleum products and by facilities, such as offshore drilling units and platforms. In 2014, vessel-related spills accounted for 40.9 percent of total gallons spilled.  While the amount of oil spilled each year varies considerably, U.S. Coast Guard data show an overall decrease in spills since 1990.