UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2565 PLYMOUTH ROAD

ANN ARBOR, MICHIGAN 48105-2498

OFFICE OF

AIR AND RADIATION

                                                                        
          	     

MEMORANDUM

SUBJECT:	Truck and Trailer Roof Height Match Analysis

FROM:		Amy Kopin

TO:		The Docket

DATE:		August 9, 2010

The aerodynamic performance of a combination truck is dependent on many
factors, including tractor and trailer size and design, the gap between
the tractor and trailer, vehicle speed, the height difference between
the cab and trailer roofs, and many others.  To assess the aerodynamic
performance of combinations trucks more accurately, certain aspects of
the truck need to be defined, including the use of a standardized
trailer during testing.  We are proposing that the standardized trailer
be determined by the roof height definition of the regulatory
subcategories, including low, mid, and high roof designs.  

Many tractors have roof fairings installed to improve aerodynamic
performance.  The height of the roof fairing is designed to minimize the
height differential between the tractor and typical trailer to maintain
a smooth, attached airflow over the vehicle and reduce the air flow
disruption, or drag.  Low roof tractors are designed to carry
platform-type trailers, which can include flatbed or low-boy trailers. 
Mid roof tractors are designed to carry tanker-type trailers, which can
include liquid and other bulk trailers.  High roof tractors are designed
to pull box-type trailers, which can include dry van trailers and
refrigerated van trailers.  However, we recognize that during actual
operation tractors may pull trailers that do not provide the optimal
roof height that matches the tractor and reduces drag.  In this
memorandum, this situation will be referred to as a “mismatch.”  In
order to assess how often truck and trailer mismatches are found, we
conducted a study based on observations of traffic across the U.S.  The
purpose of this memo is to describe how this study was carried out, and
to present the results.

The intent of the study was to sample traffic in various locations
throughout the U.S.   Originally, it was thought that truck weigh
stations might provide good sources of this information, however, the
best way to assess the height match of tractors and trailers currently
in use would be through individual counts in person, and there was not
sufficient data from truck stops to determine the trailer height.  To
avoid the need to physically travel to different sites across the
country to count trucks, which would be cost prohibitive, we determined
it was possible to sample traffic through the use of traffic cameras. 
Nearly every state has a number of traffic cameras available for public
viewing.  Some states offer a large number of available cameras for
their drivers and visitors to view; Figure 1 shows an example of the
numerous available traffic cameras in Oregon.

Figure   SEQ Figure \* ARABIC  1  Example of Available Cameras - Oregon

Source: http://www.tripcheck.com/Pages/CamerasEntry.asp

In many cases, cameras are close enough to the road to easily determine
if the tractor and trailer roof heights match; only cameras offering
these close-up views were used in this study.  Each camera used in this
study was carefully selected to provide a clear view of the truck and
trailer roof height; an example is shown below in   REF _Ref268011000 \h
 Figure 2 .  Cameras were observed between 9 AM and 6 PM as long as
clear pictures could be observed (i.e. sufficient daylight was available
to see the truck and trailer roofs and/or clement weather conditions
were present that did not obscure camera views).  Data was taken in the
last week of January, 2010 and continued through the first week of
February, 2010.  The data was taken such that at least one hundred
consecutive truck and trailer combinations were recorded from each
camera 

Figure   SEQ Figure \* ARABIC  2   Sample Image from an Oregon Camera

The study sampled images from 33 real-time traffic cameras, collecting
data on more than 4,000 tractor-trailer combinations.  Where possible,
traffic passing in both directions was used in this study.  The process
consisted of keeping count of whether or not the tractor and trailer
roof height profiles matched.  A combination was considered to be a
match if the height of the tractor roof was within a few inches of the
height of the trailer roof, for example: if a tall trailer was hauling a
tall container (as shown in   REF _Ref268011000 \h  Figure 2 ), a medium
roof tractor was hauling a tanker, and a low roof tractor was hauling a
flatbed trailer.  If the combination didn’t match, a note was made as
to what the combination was (e.g. high roof tractor with flatbed, etc.) 
Notes were also made if a tractor was empty (not hauling a trailer) or
was hauling an empty flatbed trailer.  The locations used in this study
cover 22 states across the United States, and a number of main highways,
see   REF _Ref268012020 \h  Figure 3 .  Across this broad geographic
range, we found that the cameras are located within predominately
well-populated areas, since the primary intent of these cameras is for
the public to have access to real-time traffic congestion data, which is
typically not a problem in less well-populated areas.

Figure   SEQ Figure \* ARABIC  3  Location of Cameras Where Traffic was
Observed

Based on the data gathered, approximately 95% of trucks were
“matched” per our definition (e.g. box trailers were pulled by high
roof tractors and flatbed trailers were pulled with low roof tractors). 
In general, the occurrence of a truck being lower than the trailer (e.g.
day cab and tall container) was over seven times as likely as a truck
being higher than the trailer (e.g. high roof truck and flatbed
trailer).  The amount of mismatch varied depending on the type of
location surveyed, for example over 99% of the tractors were in matched
configurations in Indiana at the I-80/I-94/I-65 interchange, which is
representative of long-haul operation.  On the other hand, in metro New
York City, the match percentage was just over 90%, in which case every
mismatched combination consisted of a day cab and a tall container,  
REF _Ref268012257 \h  Figure 4  shows the approximate locations of these
traffic cameras.

Figure   SEQ Figure \* ARABIC  4  Map of Lowest and Highest Mismatch
Percentage Found in this Study

 In addition, this study also looked at the number of trucks without
trailers or trucks hauling empty flatbeds, although the number of empty
box trailers is unknown.  It was found that of all the data included in
this study (match and mismatch counts) that approximately 3% of the
tractors were traveling without a trailer or with an empty flatbed; the
ratio between no trailer and empty flatbed trailer was approximately 50
percent.

References:

State	Website

Alabama	  HYPERLINK "http://www.dot.state.al.us/"  www.dot.state.al.us 

Arizona	  HYPERLINK "http://www.az511.gov/"  www.az511.gov 

California	  HYPERLINK "http://video.dot.ca.gov/" 
http://video.dot.ca.gov 

Colorado	  HYPERLINK "http://www.cotrip.org/"  www.cotrip.org 

Delaware	  HYPERLINK "http://www.deldot.gov/"  www.deldot.gov 

Florida	  HYPERLINK "http://www.fl511.com/"  www.fl511.com 

Iowa	  HYPERLINK "http://hb.511ia.org/main.jsf" 
http://hb.511ia.org/main.jsf 

Kansas	  HYPERLINK "http://www.kcscout.net/"  http://www.kcscout.net 

Kentucky/Ohio	  HYPERLINK "http://www.artimis.org/camaccess1.html" 
www.artimis.org/camaccess1.html 

Maine	http://maineturnpike.com/traffic_cams/traffic_cams.php

Massachusetts	  HYPERLINK "http://www1.eot.state.ma.us/" 
http://www1.eot.state.ma.us/ 

Michigan	  HYPERLINK
"http://mdotwas1.mdot.state.mi.us/public/drive/rtt.cfm" \l "1" 
http://mdotwas1.mdot.state.mi.us/public/drive/rtt.cfm#1 

Minnesota	http://www.dot.state.mn.us/tmc/trafficinfo/cameras_map.html

Mississippi	  HYPERLINK "http://www.mstraffic.com/"  www.mstraffic.com 

New York	  HYPERLINK "http://cameras.nysdot.gov/" 
http://cameras.nysdot.gov/ 

New York	  HYPERLINK "http://peacebridge.com/"  http://peacebridge.com 

North Carolina	  HYPERLINK
"http://www.greensboro-nc.gov/departments/GDOT/trafficinfo/" 
http://www.greensboro-nc.gov/departments/GDOT/trafficinfo/ 

Ohio	  HYPERLINK "http://buckeyetraffic.org/"  http://buckeyetraffic.org


Oklahoma	  HYPERLINK "http://www.oktraffic.org/"  www.oktraffic.org 

Oregon	  HYPERLINK "http://www.tripcheck.com/"  http://www.tripcheck.com


Tennessee	  HYPERLINK "http://www.tdot.state.tn.us/tdotsmartway/" 
http://www.tdot.state.tn.us/tdotsmartway/ 

Texas	  HYPERLINK "http://amaits.dot.state.tx.us/AMA-ITS/default.htm" 
http://amaits.dot.state.tx.us/AMA-ITS/default.htm 

Texas	  HYPERLINK "http://www.transguide.dot.state.tx.us/" 
www.transguide.dot.state.tx.us 



