

U.S. DEPARTMENT OF TRANSPORTATION

NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION

1200 NEW JERSEY AVENUE SE.

WASHINGTON DC, 20590	UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF AIR AND RADIATION

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2000 TRAVERWOOD DRIVE

ANN ARBOR, MI  48105-2498



July 18, 2016

MEMORANDUM

SUBJECT:	Evaluation of 50-Foot Trailer Length Demarcation to Distinguish
between Long and Short Box Vans

FROM:	Jessica Brakora, Engineer, Assessment and Standards Division

Office of Transportation and Air Quality

TO:	Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for
Medium- and Heavy-Duty Engines and Vehicles - Phase 2 - Dockets
NHTSA-2014-0132 and EPA-HQ-OAR-2014-0827



The agencies received public comments from California Air Resources
Board (CARB) and the Union of Concerned Scientists (UCS) requesting that
we change our proposed demarcation between “short” and “long”
box vans from 50-feet in length to 47-feet.  They argued that 48-foot
trailers should not be included in the short box van subcategories,
because they perform more similarly to long box vans and do not operate
in tandem, which allows manufactures to install rear aerodynamic
devices, such as tails.  This memo summarizes our evaluation of 48-foot
trailer performance, annual vehicle miles traveled, and potential
contribution to CO2 and fuel consumption reductions.

The agencies evaluated the aerodynamic performance of 48-foot box vans
in Chapter 2.10.2.1.2.6 of the RIA.    REF _Ref455506983 \h  Figure 1 
compares the performance of four dry van lengths.  The day cab (DC)
tractor is the same for the 28-foot, 48-foot, and 53-foot trailers
shown.  The 33-foot van was modeled with a MY 2014 sleeper cab in a
separate test set.  We are including the 33-foot results in the plot for
qualitative assessment.  You can see that the individual devices do not
show a consistent trend in performance based on trailer length, but
there is a noticeable trend of increased performance with increased
length for combinations of devices.  These results do suggest that the
shorter 28-foot surrogate test trailer will underestimate performance
for 48-foot trailers in its regulatory subcategory and that a 48-foot
trailer may be capable of much higher performance.  However, as
proposed, the shorter 28-foot trailer provides a conservative estimate
of performance for longer trailers in the short box van subcategories.
As a result, the agencies can be reasonably sure that most of the
trailers in the in the short box van subcategory will meet or exceed the
required performance when similar technologies applied to the 28-foot
trailer are modified to fit 48-foot trailers.  If 48-foot trailers were
included in the long box van category, manufacturers could not simply
modify technologies from long trailers; 48-foot trailers would require
additional technologies to meet the standard.

Figure   SEQ Figure \* ARABIC  1   Comparison of Aerodynamic Performance
of Devices on Several Dry Van Lengths; 2012 DC is a 6x4 Day Cab Tractor,
and 2014 SC is a 6x4 Sleeper Cab (Copy of Figure in Chapter 2.10 of the
RIA)

Another aspect to consider is the annual mileage of 48-foot trailers. 
The agencies evaluate short box van performance using short-haul drive
cycles, because we believe these trailers are more likely to travel
shorter distances and accumulate fewer miles at high speed where
aerodynamic technologies are the most effective.  The agencies
investigated “primary trip length” results from the 2002 Vehicle
Inventory and Use Survey database to determine the distribution of box
van trailers of different lengths in short- and long-haul applications.
A majority of 53-foot box vans are distinctly long-haul, but less than
30 percent of 48-foot to 52-foot vans travel more than 500 miles per
trip. Additionally, some fraction of that 30 percent is likely to be the
51-foot and 52-foot trailers that are considered long box vans in this
rulemaking.  While the fraction of box vans meeting long-haul criteria
increases if the distinguishing mileage is changed to 200 miles per trip
(  REF _Ref455508871 \h  Figure 3 ), the majority of vans in the 48-foot
to 52-foot category would still be classified short-haul.  Finally, CARB
noted in their public comment that 48-foot trailers makes up about six
percent of the overall van registrations, and only a portion of those
trailers are 48-foot.  Even if an aerodynamic improvement of up to nine
percent was possible for these trailers, the five percent additional
benefit compared to the short box van standard would only translate to
less than a half-percent reduction in CO2 and fuel consumption from
trailers. 

 

Figure   SEQ Figure \* ARABIC  2   VIUS Primary Trip Length Data for Box
Vans of Different Lengths Distinguishing Short- and Long-Haul by 500
Miles per Trip 

 

Figure   SEQ Figure \* ARABIC  3   VIUS Primary Trip Length Data for Box
Vans of Different Lengths Distinguishing Short- and Long-Haul by 200
Miles per Trip

While 48-foot vans are aerodynamically similar to longer vans and
capable of adopting additional technologies, the agencies do not believe
aerodynamic performance potential alone justifies a change in our
proposed 50-foot demarcation for long and short box vans in the Phase 2
trailer program.  48-foot vans are more likely to travel fewer annual
miles and their shorter trips indicate they are likely traveling at
slower average speeds.  These slower speeds would result in lower
real-world performance, yet these trailers would need to adopt
additional technologies compared to a 53-foot trailer in order to meet
the same long box van standards.  In addition, 48-foot trailers are
estimated to make up less than 10 percent of the van trailer population
and the additional CO2 and fuel consumption benefits would be a
relatively small improvement with more stringent standards.  The
agencies do not believe that standards predicated on the use of more
effective aerodynamic technologies on 48-foot vans will provide a
substantial enough additional reduction in CO2 emissions and fuel
consumption to justify more stringent standards for those trailers. 
For these reasons, the agencies are maintaining the proposed 50-foot
demarcation between long and short box vans.   

 

Attachment:  MemoAttachment_50ft_LengthDemarcation.xlsx

 10 U.S. Census Bureau.  2002 Economic Census – Vehicle Inventory and
Use Survey.  2002. Available at:
https://www.census.gov/prod/ec02/ec02tv-us.pdf 

Evaluation of 50-Foot Trailer Length Demarcation, Page   PAGE  3  of  
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