

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:	Comparison of GEM Drive Cycle Weightings and Fleet Data
Provided by Utility Trailer Manufacturing Co. in Public Comments

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 Utility Trailer Manufacturing
Co. (Utility) that suggested the speed distribution used to evaluate
trailer performance in GEM is not representative of real-world
operation.  Utility obtained “real-world speed data from four
fleets” and noted that two were “long-haul, nationwide carriers”
and two were “regional fleets for food-service customers”.  Utility
provided detailed speed data including percent of time spent at idle and
18 speed increments for three fleets and a general description of the
fourth fleet.  This memo includes our evaluation of the speed data
provided for the three fleets.  We are unable to address the more
general information provided for the fourth fleet.   Utility claims that
this fleet’s data confirms only small gains are achieved at high
speeds, but the comment simply noted the total mileage and indicated
that about 94% of the fuel was consumed at speeds below 55 mph, without
any additional details.  

The first four columns of   REF _Ref455477832 \h  Table 1  (light gray)
reproduce the three fleets’ speed data provided by Utility in its
comments.  Note that these data include time at idle.  However, the
trailer does not impact CO2 or fuel consumption when the vehicle is in
idle.  No additional energy is required to pull the payload, or overcome
drag and rolling resistance when the vehicle is not in motion.  With the
exception of technologies related to the transport refrigeration unit
(TRU) of refrigerated trailers, which is out of scope of this
rulemaking, the agencies are not aware of any trailer technologies that
increase or reduce fuel use when the vehicle is idling.  Therefore, we
do not consider idle when we estimate our per-vehicle performance for
compliance using GEM.  Additionally, the data was provided as percent
time at a given speed.  GEM’s drive cycle weightings are
distance-based, and considers the amount of distance traveled at each
speed instead of time at each speed.  To ensure we are making an
appropriate apples-to-apples comparison between the data provided and
our current GEM drive cycle weightings, we converted Utility’s data to
reflect the format required by GEM.  The results are shown in the last
three columns of   REF _Ref455477832 \h  Table 1  and the intermediate
calculations are available in the attached Excel spreadsheet.  

Table   SEQ Table \* ARABIC  1   Speed Data for Three 53-Foot Box Van
Fleets 

Cruising Speed 

(mph)	% Time at Speed*	% Distance at Speed**

	Fleet 1	Fleet 2	Fleet 3	Fleet 1	Fleet 2	Fleet 3

0.0	38.57%	14.70%	20.26%	0.0%	0.0%	0.0%

2.5	2.37%	1.76%	2.33%	0.2%	0.1%	0.1%

7.5	2.38%	2.39%	3.60%	0.6%	0.4%	0.6%

12.5	1.53%	1.48%	2.80%	0.6%	0.4%	0.8%

17.5	1.13%	1.05%	1.81%	0.6%	0.4%	0.8%

22.5	1.03%	1.04%	1.50%	0.8%	0.5%	0.8%

27.5	1.13%	1.13%	1.07%	1.0%	0.7%	0.7%

32.5	1.23%	1.18%	2.80%	1.3%	0.8%	2.2%

37.5	1.47%	1.29%	1.38%	1.8%	1.1%	1.2%

42.5	2.35%	1.71%	1.60%	3.2%	1.6%	1.6%

47.5	1.78%	2.50%	1.14%	2.7%	2.6%	1.3%

52.5	4.35%	6.37%	1.50%	7.4%	7.3%	1.9%

55.0	3.15%	6.78%	4.05%	5.6%	8.2%	5.4%

57.5	4.25%	10.29%	3.74%	7.9%	12.9%	5.2%

59.5	10.62%	12.41%	3.74%	20.5%	16.1%	5.3%

61.5	19.63%	12.10%	5.00%	39.2%	16.3%	7.4%

63.5	1.68%	11.64%	15.60%	3.5%	16.2%	23.8%

65.0	1.35%	10.19%	25.71%	2.9%	14.5%	40.1%

70.0	0.00%	0.00%	0.38%	0.0%	0.0%	0.6%

*    Speed data provided by Utility in public comments

**  Utility’s speed data converted to GEM’s distance-based format

Utility’s comment also included a graph that compared the three fleets
speed to the three drive cycles in GEM that is copied in   REF
_Ref455481260 \h  Figure 1 .  Utility cited a disconnect between the GEM
drive cycles and the real-world data provided.  However, as mentioned
previously, the data provided in the comment was time-based and it is
not appropriate to compare time-based data to GEM’s distance-based
drive cycle weightings.  In   REF _Ref455481739 \h  Figure 2 , the
agencies used the converted “% Distance at Speed” data from   REF
_Ref455477832 \h  Table 1  and recreated the comparison of   REF
_Ref455481260 \h  Figure 1  with consistent units for the data.

While Utility’s comment suggested that GEM “dramatically exceeds
what the real-world data shows”,   REF _Ref455481739 \h  Figure 2 
shows that the difference is not as drastic when consistent units are
used.  In fact, the GEM model appears to overestimate the distance
traveled at speeds lower than 30 mph compared to the real-world data
provided.  Utility also noted that the weighted average speed for GEM is
62 mph, but the fleet data was between 30 mph and 45 mph.  However, when
considering distance-based speeds, the average speed for the three
fleets is actually 58 mph. 

Figure   SEQ Figure \* ARABIC  1   Percent of Time at Speed Figure
Copied Directly from Utility’s Public Comments

 

Figure   SEQ Figure \* ARABIC  2   Percent of Distance at Speed
Comparison of GEM’s Long Haul Drive Cycle Weightings and Utility’s
Fleet Data from Public Comments Converted to Distance-Based Units

The agencies acknowledge that the current GEM weighting for percent of
distance at 65 mph is greater than is seen in these three fleets and
that devices evaluated at 65 mph would not perform as well for these
fleets.  However, GEM’s fraction of 55 mph is lower, yet aerodynamic
devices are nearly as effective at 55 mph compared to 65 mph (about a
20% difference).  It may be more effective to consider low and high
speed operation to evaluate whether the GEM drive cycle weightings are
appropriate.  If we create two bins of speed with 55 mph as the
demarcation,   REF _Ref455491937 \h  Figure 3  shows that the three
fleet’s data provided by Utility, which includes at least one regional
food service fleet, is much more similar to the GEM drive cycles.  

 

 

Figure   SEQ Figure \* ARABIC  3   Percent of Distance at Speed when
Speed Data is Combined into Low and High Speed Bins

These results suggest that the fleet data provided by Utility is not
substantially different than the current GEM drive cycle weightings. 
The results indicate that the fleets are not traveling a majority of
their miles at speeds that would have minimal benefit from the
technologies that are the basis of the Phase 2 trailer program; the data
generally indicates the reverse. Additionally, while there are some
differences in the fraction of distance at 65-mph, there is no
indication that the data from these three fleets is representative of
nationwide tractor-trailer operation.  Therefore, the agencies do not
believe that these limited data justify new drive cycle weightings for
the Phase 2 trailer program.  

Attachment:  MemoAttachment_DriveCycleComparison_Utility.xlsx

Comparison of GEM Drive Cycle Weightings and Fleet Data Provided in
Public Comments, Page   PAGE  4  of   NUMPAGES   4 

