Deadheads, which may conjure up images of revelers in tie dye, are legs driven by truckers with no cargo. Empty trucks on a return trip populate the roadways while pumping pollutants into the atmosphere. If a network could match needed shipments with these carriers on their return trips, deadheads could be eliminated. What is the potential environmental savings? One approach is to calculate how much carbon is being emitted by these empty trucks.
How many miles?
The Vehicle Inventory and Use Survey, last put out by the US Census Bureau in 2002, offers a breakdown of freight miles by cargo type. Some of the information pertinent to this calculation include the cargo type, annual mileage, and annual empty mileage.¹ Across all cargo types, it is estimated that there were nearly 29 billion empty miles.²
Despite the value of this information, 2002 was the last time this survey was undertaken due to funding cuts. The need for this dataset is evident as it is still being cited in federal studies today. The Bureau of Transportation Statistics, in its 2015 Freight Facts and Figures, calls for this survey to be restored and provides an update on a joint commission that would do so.
Public trucking companies are not obligated to report empty miles as part of its SEC filing, and private companies certainly have no incentive to report this metric. However, some of the largest carriers do provide this information. While anecdotal, these data points represent a significant portion of the fleet and serve as useful benchmarks. Werner Enterprises, a top ten US truckload carrier,³ reports between 12% and 13% empty miles annually in from 2014–2016.⁴ From J.B. Hunt’s reporting of total and loaded miles, its JBT (truckload) segment tallied 33 million empty miles, or 16% of its total.⁵ The largest truckload carrier, Swift Transportation, reports running 12.1% empty in both 2015 and 2016.⁶This percentage equates to over 122 million empty miles in 2016.
Further validation comes from the American Trucking Association, which reports 279.1 billion miles driven by all registered trucks in 2014. Combination trucks accounted for 61% of this portion or 169.8 billion miles. The Environmental Defense Fund estimates 15–25% of truck miles are empty. Using the low end of this range, assuming carriers operate with a deadhead rate of 15% of their total miles, yields 41.9 billion empty miles for all trucks and 25.5 billion empty miles for combination vehicles.
How much does an empty truck weigh?
Numerous variables and configurations result in a range for estimating the weight of an empty truck. Consider an actual deadhead trip with effects, not simply the manufacturer’s weight specification for the truck. Our case assumes a dry van truck. Contributing factors to the vehicle’s weight include cab choice (day, sleeper, or crew), engine size and model, number of axles, trailer and cargo securing equipment, and personal effects.
Tractors can weigh from 15,000 to over 20,000 pounds, again depending on many size and power choices. The trailer can also have a variety of lengths and axle options. Dry vans at 53 feet in length can weigh in at over 15,000 pounds, while lightweight options can weigh under 11,000 pounds. Shorter dry vans are lighter; 48 foot long dry vans can weigh under 10,000 pounds. While the heaviest tractor trailer configurations can approach 40,000 pounds empty, a conservative average tractor trailer empty weight of 28,750 pounds was used for this calculation.⁷
How much carbon is emitted?
Approximately 12% of diesel exhaust is carbon dioxide. Encompassing all medium and heavy duty diesel trucks, 369.4 million metric tons of carbon dioxide were emitted in 2015.⁸ EPA Smart Way reports 161.8 grams of carbon dioxide are released for every ton mile driven.⁹
Using the 2002 Vehicle Inventory and Use Survey mileage, carbon emissions are calculated in Table 1, below:
Sixty-seven million metric tons of carbon dioxide are emitted by empty trucks annually according to the calculation above. This amount represents the total carbon emissions across all cargo types. While the empty miles quantity is sourced from a 2002 value, according to the Bureau of Transportation Statistics, freight trucking miles have increased approximately 20% from 2002 to 2015.¹⁰
Using the ATA truck mileage of all registered trucks with the EDF estimated deadhead percentage, carbon emissions as calculated in Table 2:
The carbon emissions figure rises to over 97 million tons of carbon dioxide. This computed figure is across all registered truck types. This amount needs to be narrowed down to focus on emissions produced just by heavy trucks. Taking the mileage from combination trucks, reported by the ATA, yields the calculations shown in Table 3:
The 59 million metric tons of carbon dioxide is just from combination trucks. This refined figure gets closer to the quantity available to be reduced with improved class 8 truck deadhead operations.
There are alternative methods to calculate carbon emissions. One approach would be to determine the total diesel fuel consumption of class 8 trucks. Another would be to survey and calculate brake specific fuel consumption rates or overall efficiencies for truck engines. A third would be to determine the fuel consumption (miles per gallon) of empty class 8 trucks. Fuel consumption per truck is a function of several variables including weight, engine efficiency, tire pressure, air resistance, route elevation change, speed, and wind resistance. The range appears to be from 6 miles to 12 miles per gallon.
Other pollutants are present in diesel fuel. Through combustion, nitrogen, sulfur compounds, and particulates are emitted into the atmosphere. Technologies that treat diesel exhaust are in place. Further analysis to quantify the amounts of these exhaust components is warranted.
This study focused purely on empty trucks. Underutilized capacity of partially loaded trucks also represents a potential savings. Filling up space on trucks already traveling a route negates the need to employ another truck traveling in the same direction and will unlock further carbon savings potential.
1. US Census Bureau, 2002 Economic Census, Vehicle Inventory and Use Survey (December 2004). Retrieved from: https://www.census.gov/svsd/www/vius/2002.html
2. US Department of Transportation, Bureau of Transportation Statistics. (2016). 2015 Freight Facts and Figures.
3. Top 50 Trucking Companies of 2016: Reinventing the fundamentals Retrieved from: http://www.logisticsmgmt.com/article/top_50_trucking_companies_of_2016
4. Werner Enterprises, Inc.. (2017). Annual Report 2016. Retrieved from: http://investor.werner.com/ ﬁnancial-information/annual-reports/default.aspx
5. JB Hunt . (2017). Annual Report 2016. Retrieved from: http://www.jbhunt.com/company/ newsroom/presentations/
6. Swift Transportation, Inc.. (2017). Annual Report 2016. Retrieved from: http://investor. knight-swiftinc.com/sites/knighttrans.investorhq.businesswire.com/ﬁles/event/additional/ Final_Annual_Report_2016.pdf
7. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles, National Research Council of the National Academies, 2010.
8. US Environmental Protection Agency, US Transportation Sector Greenhouse Gas Emissions, 1990–2015.
9. U.S. Environmental Protection Agency’s Smartway Transport Partnership Program / Recommendations and Findings, Public Export, 2014.
10. Federal Motor Carrier Safety Administration, 2017 Pocket Guide to Large Truck and Bus Statistics, June 2017.