Evaluation of the Proposed SmartWay Fuel Efficiency Test Protocol 

for Medium- and Heavy-duty Vehicles 

 Report A: Conventional and Hybrid Utility Trucks 

ERMS Report No 08-38 

Prepared by 

Martha Christenson 

Emissions Research and Measurement Section 

Environment Canada 

Justin Greuel 

Office of Transportation & Air Quality 

U.S. Environmental Protection Agency 
NOTICE

________________________________________________________________

This report has not undergone detailed 

technical review by the Science and 

Technology Branch. The content does not 

necessarily reflect the views and policies of 

Environment Canada. Mention of trade names 

or commercial products does not constitute 

endorsement for use. 

This unedited version is undergoing a limited 

distribution to transfer the information to people 

working in related studies. This distribution is 

not intended to signify publication and if the 

report is referenced, the author should cite it as 

an unpublished report of the Directorate 

indicated below. 

Any comments concerning its content should 

be directed to: 

Environment Canada 

Air Quality Research 

Science and Technology Branch 

335 River Road 

Ottawa, Ontario, Canada K1A 0H3 

2
ACKNOWLEDGEMENTS 

The authors gratefully acknowledge the staff of the Emissions Research and 

Measurement Section of Environment Canada for undertaking the work 

described in this report, the U.S. Environmental Protection Agency’s Office of 

Transportation & Air Quality for recruiting the test vehicles and providing 

feedback and support throughout testing and reporting, Florida Power & Light for 

donating the two test vehicles, and Eaton Corporation for providing technical 

support. 

Funding for this project was provided by Environment Canada, and the Natural 

Resources Canada Program of Energy Research and Development: specifically 

the Electric Mobility Program. 

3
1.0 INTRODUCTION................................................................................................................... 5

2.0 VEHICLE INFORMATION.................................................................................................. 6

3.0 FUEL PROPERTIES.............................................................................................................. 7

4.0 PROCEDURE.......................................................................................................................... 7

4.1 DRIVING CYCLES...................................................................................................................... 7

4.2 DUTY LOAD CYCLES .............................................................................................................. 10

4.3 DYNAMOMETER SET-UP......................................................................................................... 11

5.0 DATA ACQUISITION AND ANALYSIS........................................................................... 15

6.0 RESULTS............................................................................................................................... 17

6.1 TARGET VS. ACTUAL DRIVE CYCLE AND DUTY CYCLE...................................................... 17

6.2 DRIVE CYCLE RESULTS ......................................................................................................... 19

6.3 DUTY CYCLE AND IDLE RESULTS........................................................................................... 24

6.4 SAMPLE SIZE CALCULATION AND STATISTICS .................................................................... 30

6.5 FUEL EFFICIENCY IMPROVEMENTS AND EMISSION REDUCTIONS ..................................... 31

6.6 COLD TEMPERATURE IMPACTS ............................................................................................ 35

7.0 CONCLUSIONS AND RECOMMENDATIONS .............................................................. 36

REFERENCES ............................................................................................................................ 38

APPENDIX A – VEHICLE SPECIFICATIONS ..................................................................... 40

4
1.0 INTRODUCTION 

The new SmartWay Fuel Efficiency Test Protocol [1] was developed by the U.S. 

EPA with the goal of providing a standardized, objective, consistent test 

procedure to measure the fuel consumption of medium and heavy duty vehicles 

used in on-road applications. The protocol is intended to be used on a voluntary 

basis to determine if vehicles meet SmartWay performance specifications. The 

procedure covers heavy duty vehicles as defined by 40 CFR §86.082-2 and 

§86.090-2. These vehicles are rated at over 8,500 lbs GVWR, or have a curb 

weight of more than 6,000 lbs, or have a basic vehicle frontal area of over of 45 

square feet. 

In addition to determining if vehicles meet SmartWay performance specifications, 

the new protocol provides a method for benchmarking new technologies and 

comparing vehicle designs within a given application. Existing certification 

requirements for heavy duty vehicle manufacturers are based on the U.S. EPA 

emission standards for engines (40 CFR Part 86, Subpart N) and do not take into 

account benefits from hybrid drive-trains or other efficient designs (improved 

aerodynamics, low rolling resistance tires etc.). 

The Emissions Research and Measurement Section (ERMS) of Environment 

Canada, in collaboration with the U.S. EPA, is providing input to the evaluation 

and refinement of the new SmartWay test protocol. The ERMS is performing the 

chassis dynamometer portion of the SmartWay Test Protocol at its test facility in 

Ottawa, ON, and providing feedback to the U.S. EPA on the draft protocol. Prior 

to these dynamometer tests, track tests (including road load measurements 

using coastdown techniques) were completed at the Aberdeen Test Center 

(ATC) in Aberdeen, Maryland. Vehicles covered by the draft protocol include both 

conventional and hybrid versions of utility trucks, transit buses, refuse haulers, 

class 8 line haul trucks, and parcel delivery trucks. Goals of this test program 

include: 

• Refinement of the SmartWay Test Protocol 

• Quantification of benefits provided by hybrid vehicles 

• Establishment of a relative equivalence between track and chassis 

dynamometer testing 

• Quantification of test to test variability 

• Evaluation of the proposed statistical methods 

• Determination of the impacts of PTO and auxiliary loads 

• Assessment of the adequacy of tolerances for target vs. actual trace 

speeds during chassis dynamometer testing 

• Characterization of typical CO2 emission rates 

The following report conveys results of the first round of testing conducted at the 

ERMS, and provides recommendations for future testing and refinements of the 

SmartWay Test Protocol. The draft protocol was used to conduct emissions and 

fuel consumption testing on two utility boom trucks in August and September, 

5
2008. The conventional vehicle was an International 4300 chassis with a Navistar 

DT466 engine, an Allison 5-speed automatic transmission, and an Altec L42A 

(42 ft) aerial boom. The hybrid vehicle had a similar chassis, engine, and boom, 

but incorporated an Eaton parallel hybrid electric system in place of the standard 

transmission. 

The SmartWay Test Protocol proposes use of the Composite International Truck 

Local Cycle and Commuter (CILCC) transient cycle for chassis dynamometer 

and track testing of utility boom trucks. The protocol acknowledges the need to 

account for power take-off (PTO) operational loads, but proposes no specific duty 

cycles for testing. For purposes of this test program, a 10-minute idle test was 

employed and EPA staff recommended two additional duty cycles developed for 

a similar study [3] at the Southwest Research Institute (SwRI). Additional testing 

was performed to evaluate system sensitivities on other standard drive cycles 

and cold climate performance. This included testing on the LA4 drive cycle at 

standard temperature (22o

C), and on the heavy duty UDDS drive cycle at both 

22oC and -7oC. Lastly, testing was conducted on a standard drive cycle with 10% 

road load reduction to evaluate the effects of potential variability in coastdown 

techniques. 

2.0 VEHICLE INFORMATION 

The vehicles tested were conventional and hybrid utility boom trucks, pictured in 

Figure 1. The trucks had similar chassis and hydraulic systems, but one had a 

conventional drive train, while the other used Eaton Corporation’s1 parallel hybrid 

electric drive train. Both vehicles were equipped with EGR and oxidation 

catalysts. Vehicle specifications are given in Appendix A. 

 Figure 1: Conventional and hybrid utility trucks 

 

1

 Further specifications on the hybrid system can be found in Eaton Publication EH-8E306A-CD 

at http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&dID=250730. All specifications are 

identical to the system tested with the exception of the high-voltage battery system. The system 

tested utilized nickel-metal hydride batteries instead of lithium ion batteries. 

6
3.0 FUEL PROPERTIES 

The fuel used was ULSD Type 2-D distillate (reference 40 CFR §86.1313-2007), 

and had the properties listed in Table 1. Fuel analysis was performed by the 

Alberta Research Council. 

Table 1: Fuel Properties 

U.S. EPA ULSD #2D

Density (kg/m3@15°C) 845.9 

Specific Gravity (kg/L, 60/60°F) 0.8463 

Gravity deg API=141.5/SG-131.5 35.7 

Cetane Number (ASTM D613) 44.9 

Carbon (wt%) 86.24 

Hydrogen (wt%) 13.41 

Nitrogen (ppm) 3.66 

Total Sulfur % (max) 0.000011

Total Sulfur (ppm) 11 

Volume % Aromatics 28.3 

% Olefins 3.4 

% Saturates 68.3 

Flashpoint, min 0C 68 

Cloud Point max °C -22 

Kinematic Viscosity, Centistokes 2.455 

Net Heating Value (btu/lb) 18313 

Net Heating Value MJ/kg 42.6 

IBP (initial boiling point) 125.3 

10% 188.4 

50% 261.2 

90% 329 

End Point 389 

4.0 PROCEDURE 

Three driving cycles, two duty load cycles, and a 10-minute idle test were 

employed to investigate fuel consumption and emission rates of the utility trucks. 

Cold temperature impacts were examined on select cycles for both hybrid and 

conventional trucks. 

4.1 Driving Cycles 

Characteristics of each driving cycle are given in Table 2 and the cycles are 

described in the following sections. 

7
Table 2: Driving Cycle Characteristics 

Ave 

Speed 

(mph) 

Stdev. 

Speed 

Max 

Speed 

(mph) 

Max 

Accel. 

(mph/s) 

Max 

Decel 

(mph/s) 

Total time 

(s) 

Idle time 

(s) 

Total 

Dist. 

(mi) 

No. of 

Idle 

Periods

LA4 19.6 14.7 56.7 3.3 -3.3 1370 260 7.45 18 

HD UDDS 18.84 19.84 58 4.19 -4.51 2121 706 11.1 27 

CILCC 13.89 12.4 55 2.5 -2.5 3192 562 12.32 25 

Combined International Local and Commuter Cycle (CILCC): 

The CILCC was developed by the U.S. Department of Energy’s National 

Renewable Energy Laboratory, Eaton Corporation, and International Truck and 

Engine Corporation. The CILCC speed vs. time sequence is given in Figure 2. 

This cycle is currently recommended in the SmartWay Test Protocol draft 

document for utility service truck testing. The cycle has an average speed of 13.9 

mph, a maximum speed of 55 mph, and covers a distance of 12.3 mi with 25 

stops. 

CILCC Driving Cycle

0

10

20

30

40

50

60

0 500 1000 1500 2000 2500 3000

Time (sec)

Speed, mph

Figure 2: CILCC Speed vs. Time Schedule 

LA4 Cycle:

The LA4 drive cycle (also known as the Urban Dynamometer Driving Schedule or 

UDDS) was developed by the U.S. EPA to simulate low speed urban driving with 

mild accelerations, and is currently used as part of the Federal Test Procedure 

for determining light-duty vehicle emissions compliance in North America. The 

cycle has an average speed of 19.6 mph and a maximum speed of 56.7 mph. 

The speed vs. time schedule is shown in Figure 3. 

8
LA4 Driving Cycle

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400

Time (sec)

Speed, mph

Figure 3: LA4 Speed vs. Time Schedule 

Heavy-Duty UDDS

The heavy-duty urban dynamometer driving cycle (HD UDDS) was developed by 

the U.S. EPA for heavy duty vehicle chassis dynamometer testing, and is the 

basis for the FTP transient engine dynamometer cycle. It has an average speed 

of 18.9 mph and maximum speed of 58 mph. The HD UDDS speed vs. time trace 

is shown in Figure 4. 

9
HD UDDS

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200

Time (sec)

Speed, mph

Figure 4: HD UDDS Speed vs. Time 

4.2 Duty Load Cycles 

Two hydraulic load cycles were recommended by U.S. EPA staff to evaluate 

emissions and fuel consumption during operation of the hydraulic lift arm. The 

pressure vs. time schedules are shown in Figure 5 and Figure 6 and have been 

sourced from a SwRI study [3]. 

Attempts were made to attain the required pressures by raising the lift arm using 

the boom operator hand controls and rotating it for the specified times. To 

achieve the lower pressure at the end of Duty Cycle B, low-idle mode was used 

on the conventional truck. This was not available for the hybrid truck, and 

therefore the lowered pressure at the end of Duty Cycle B was not possible. In 

the previous study at SwRI, an auxiliary circuit was connected to the truck’s 

hydraulic tool connection port to artifically load the system, and this allowed for 

consistent and accurate loading. Such a circuit is specialized and is not currently 

available at most emission test facilities. 

10
Duty Load A

0

500

1000

1500

2000

2500

0 500 1000 1500 2000

Time (sec)

Pressure (PSI)

Figure 5: Duty Cycle A 

Duty Load B

0

500

1000

1500

2000

2500

0 500 1000 1500 2000

Time (sec)

Pressure (PSI)

Figure 6: Duty Cycle B 

4.3 Dynamometer Set-up 

Vehicles were tested on a single roll chassis dynamometer system with a 0.61m 

(24 inch) diameter roll. Before testing, it was necessary to override the hybrid 

vehicle’s anti-lock brake system (ABS) fault codes for driving on the two-wheel 

(single roll) dynamometer. Otherwise, the vehicle’s ABS would interpret nonrotation of the front set of wheels as a malfunctioning system. This would 

inadvertently affect normal operation of the remaining vehicle systems, including 

11
engine transmission and the regenerative braking system. It was also necessary 

to disable augmented braking on the dynamometer in order to accurately 

simulate inertia and road load during braking and allow for proper functioning of 

the regenerative braking system. The inertia weight and road loads were 

simulated during testing using a 400 Hp direct current motor. The chassis 

dynamometer inertia weights were set at 20,242 lbs for the conventional truck 

and 23,062 lbs for the hybrid truck. The truck weights were provided by the U.S. 

EPA based on the actual weights taken at each wheel. A fixed speed fan was 

used to provide engine cooling air. 

On-road coast downs had previously been performed in accordance with SAE 

J2263 on a 3 mile test track at the Aberdeen Test Center (ATC) in Aberdeen, 

Maryland. Although the procedure recommends coasting down from 71.5 mph to 

9.3 mph, the maximum speed was only 65 mph because the test vehicles were 

speed governed at this speed. It should be noted that J2263 is traditionally used 

for determining road load of light-duty vehicles and its use may be questionable 

for heavy-duty applications. Prior to conducting coast down runs for the hybrid 

truck, EPA confirmed with Eaton that regenerative braking would not be active 

while the transmission was in neutral. 

The ERMS was provided with data for five coast downs in each direction for each 

vehicle. Dynamometer target coefficients were derived from the resulting speedtime data, and dynamometer set coefficients were obtained by performing coast 

downs on the chassis dynamometer according to SAE J2264. Target and set 

coefficients, as defined in SAE J2264 §3.12 with units changed to HP @ 50 mph, 

are provided in Table 3. 

Table 3: Road load coefficients (HP @ 50mph) 

Coefficients A B C 

Target 22.2 0 39 Conventional 

Set 5.742 -5.493 37.566 

Target 26.9 0 39 Hybrid Set 8.776 -4.949 37.948 

Speed vs. time for each of the on-road coast downs is shown in Figure 7, along 

with the corresponding dynamometer speed–time data generated after 

dynamometer calibration according to SAE J2264. On-road, the speeds were 

relatively consistent from run to run between 65 and 30 mph. Between 30 and 15 

mph, the conventional vehicle slowed more quickly than the hybrid vehicle. In 

fact, the deceleration rate of the hybrid vehicle decreased substantially between 

30 and 20 mph. Below approximately 15 mph, however, the hybrid’s speed 

dropped quickly and the hybrid came to rest, on average, more rapidly than the 

conventional vehicle. This contradicts the SwRI study [3], where the hybrid took 

longer to coast down than did the conventional vehicle. 

12
0

10

20

30

40

50

60

70

80

-10 40 90 140 190 240 290 340 390 440 490

Time [s]

Speed [mph]

Hy Run 1

Hy Run 2

Hy Run 3

Hy Run 4

Hy Run 5

Hy Run 6

Hy Run 7

Hy Run 8

Hy Run 9

Hy Run 10

Conv. Run 1

Conv. Run 2

Conv. Run 3

Conv. Run 4

Conv. Run 5

Conv. Run 6

Conv. Run 7

Conv. Run 8

Conv. Run 9

Conv. Run 10

Hybrid Dyno Speed

Conv. Dyno Speed

Figure 7: Speed vs. time for coast-downs on-road, and on the chassis dynamometer 

Road load (Figure 8) was higher for the hybrid compared to the conventional 

vehicle. At 60 mph, the road load experienced by the hybrid was 5.5 HP higher 

than for the conventional truck. The difference between target road load power 

and the dynamometer power setting provides an indication of the parasitic power 

losses in the vehicle drive train. 

13
0

20

40

60

80

100

120

0 10 20 30 40 50 60 7

Speed [mph]

HP

0

Hybrid Target RL

Hybrid Dyno Settings

Conv. Target RL

Conv. Dyno Settings

Figure 8: Road load targets and dynamometer settings 

Figure 9 shows road load versus speed curves for the hybrid utility truck. The 

“Road Load Used” curve represents the road load experienced by the truck 

during testing. This curve is based on an average of all 10 on-road coast downs. 

To illustrate the variability in the on-road coast down data, the minimum and 

maximum road-load curves calculated from individual on-road coast downs are 

shown. 

The “10% Reduced Road Load” curve, shown in light blue, is a curve calculated 

based on a 10% reduction in each road load coefficient of the “Road Load Used” 

curve. This should represent, approximately, the road load experienced by the 

utility truck during the “10% Reduced Road Load” tests performed on the hybrid 

utility truck. It should be noted that the 10% reduction was only applied to the set 

coefficients, so the curve shown in Figure 9 may slightly over-estimate the 

reduction in road-load experienced by the truck during testing. 

14
0

20

40

60

80

100

120

0 10 20 30 40 50 60 7

Speed [mph]

HP

0

Road Load Used

Minimum Road Load

Maximum Road Load

10% Reduced Road Load

Figure 9: Road load variability for hybrid utility truck 

5.0 DATA ACQUISITION AND ANALYSIS 

An SAE J1939 compliant Nexiq USB-Link and Eaton Service Ranger software 

were provided by Eaton for recording hybrid battery state of charge (SOC) data. 

In order to measure hydraulic pressure, a pressure transducer (model PX35D0-

3KGV with serial number 39246) was connected to the truck’s hydraulic tool 

connection port located near the boom operator hand controls (see Figure 10). 

Prior to use the transducer was calibrated by Omegadyne Inc. between 0 and 

3000 PSI. 

15
Figure 10: Hydraulic tool port 

The total exhaust stream produced by each truck was collected and diluted using 

a constant volume sampling (CVS) dilution system with a total dilute exhaust 

volume of 2000 scfm. The dilution air was taken from the test cell and was 

conditioned by HEPA filtration for removal of particulate matter. The total volume 

of raw exhaust was transferred from each truck to the CVS through a 6 inch 

diameter flexible, stainless steel pipe that was insulated. The raw exhaust was 

then diluted with laboratory air and the mixture directed through a critical flow 

venturi. During the exhaust emissions test continuously proportioned samples of 

the dilute exhaust mixture and the dilution air were collected and stored in 

sample bags for analysis. 

Table 4 summarizes the exhaust sample collection and analysis method for each 

compound. 

Table 4: Exhaust Sample Collection and Analysis 

Compound Analysis Method Sample Collection 

Carbon Dioxide Non-Dispersive Infrared 

Detection (NDIR) 

Continuous Collection (Dilute Exhaust 

Only) 

As well as TedlarTM Bag 

Carbon Monoxide Non-Dispersive Infrared 

Detection (NDIR) 

Continuous Collection (Dilute Exhaust 

Only) 

As well as TedlarTM Bag 

Oxides of Nitrogen Heated Chemiluminescence 

Detection 

Continuous Collection (Dilute Exhaust 

Only) 

As well as TedlarTM Bag 

Total Hydrocarbons Heated Flame Ionization 

Detection (FID) 

Continuous Collection (Dilute Exhaust 

Only) 

16
As well as TedlarTM Bag 

Methane and Light 

Hydrocarbons 

Gas Chromatography Tedlar TM Bag 

Aldehydes High Performance Liquid 

Chromatography (HPLC) 

Sep-Pak silica cartridges coated with 

2,4- 

dinitrophenylhydrazine (2,4-DNPH) 

Total Particulate 

Matter Mass 

Gravimetric EMFAB Filter 

6.0 RESULTS 

6.1 Target vs. Actual Drive Cycle and Duty Cycle 

Actual dynamometer speeds were well within the tolerances based on regression 

analysis as specified in SAE J2711. An example of the “driven” versus 

“commanded” speed regression is given in Figure 11. The hybrid truck lagged 

during the second hill of the LA4, and could not meet the acceleration 

requirement. The speed, however, remained within the tolerances. 

y = 0.9859x

R2

 = 0.9925

0

10

20

30

40

50

60

0 10 20 30 40 50 6

Commanded Speed [MPH]

Driven Speed [MPH]

0

Figure 11: Example of "commanded" versus "driven" speed on the CILCC 

On the duty cycles, it was difficult to achieve consistent and controlled hydraulic 

loading according to the prescribed schedule. Examples of the pressures 

obtained on Duty Cycle B are given in Figures 12 and 13. Maximum pressures 

17
occasionally reached 1900 PSI as required by the time vs. pressure schedule, 

but were typically between 1400 and 1700 PSI. Also, it was not possible to 

generate the lower pressure at the end of Duty Cycle B with the hybrid because 

the “low-idle” option was not available. These differences must be taken into 

account when comparing results to those of the SwRI utility truck tests [3], where 

an auxiliary hydraulic loading tool was used to simulate operation of the lift arm in 

a controlled manner. 

Duty B - Conventional

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 200 400 600 800 1000 1200 1400 1600 1800

Time [sec]

Pressure [PSI]

Run 1

Run 2

Run 3

Cycle

Figure 12: Target vs. Actual Duty Cycle B Conventional 

18
Duty B - Hybrid

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 200 400 600 800 1000 1200 1400 1600 1800

Time [sec]

Pressure [PSI]

Run 1

Run 2

Run 3

Cycle

Figure 13: Target vs. Actual Duty Cycle B Hybrid 

6.2 Drive Cycle Results 

Emissions and fuel consumption results for the drive cycles are given in the 

following Tables and Figures. State of charge (SOC) at the start and end of each 

test, as well as the battery net energy change (NEC), total cycle energy (TCE) 

and the NEC/TCE ratio are also provided in the tables. For the drive cycles, the 

NEC/TCE was always within the SAE J2711 tolerance of 1%, and therefore no 

fuel consumption or emission rate corrections were made. 

Table 5: Emissions and Fuel Consumption over the CILCC 

 CO 

(g/mi) 

Nox 

(g/mi) 

HC 

(g/mi) 

PM 

(g/mi) 

CO2 

(g/mi) 

FC 

(L/100km) 

FC 

(mpg) 

NEC/TCE 

(%) 

TCE 

(kWh) 

Batt. 

NEC 

(kWh) 

SOC 

Start 

(%) 

SOC 

End 

 (%) 

Warm Up 2.58 11.10 0.19 na 1368.09 31.7 7.4 - - - - - 

Run 1 2.33 7.96 0.22 0.065 1232.21 28.6 8.2 - - - - - 

Run 2 2.42 7.86 0.17 0.070 1179.80 27.4 8.6 - - - - - 

Run 3 2.41 8.54 0.25 0.064 1225.26 28.4 8.3 - - - - - 

AVE 2.38 8.12 0.21 0.066 1212.42 28.13 8.4 - - - - - 

CILCC 

Conv. 

COV (%) 2 5 19 5 2 2 2 - - - - - 

Warm Up 4.91 5.00 0.34 na 1138.85 26.5 8.9 -0.24 52.07 -0.13 47.6 40.8 

Run 1 2.01 6.22 0.28 0.099 1076.31 25.0 9.4 -0.05 49.52 -0.02 40.8 39.6 

Run 2 1.93 6.37 0.29 0.083 1069.03 24.8 9.5 0.00 48.85 0.00 39.6 39.6 

Run 3 1.99 6.08 0.28 0.088 1058.67 24.6 9.6 0.02 48.09 0.01 39.6 40.0 

AVE 1.98 6.22 0.28 0.090 1068.00 24.78 9.49 

CILCC 

Hybrid 

COV (%) 2 2 3 9 1 1 1 

19
Table 6: Emissions and fuel consumption over the UDDS 

 CO 

(g/mi) 

Nox 

(g/mi) 

HC 

(g/mi) 

PM 

(g/mi) 

CO2 

(g/mi) 

FC 

(L/100

km) 

FC 

(mp

g) 

NEC/ 

TCE 

(%) 

TCE 

(kWh) 

Batt. 

NEC 

(kWh) 

SOC 

start 

(%) 

SOC 

end 

(%) 

Warm Up 0.45 9.03 0.24 na 1424.48 33.0 7.1 - - - - - 

Run 1 1.55 6.97 0.19 0.133 1363.59 31.6 7.4 - - - - - 

Run 2 1.53 6.56 0.19 0.115 1326.39 30.7 7.7 - - - - - 

Run 3 1.48 6.59 0.17 0.130 1338.65 31.0 7.6 - - - - - 

AVE 1.52 6.70 0.18 0.126 1342.88 31.1 7.6 - - - - - 

UDDS 

Conv. 

22o

C 

COV (%) 2 3 6 8 1 1 1 - - - - - 

Warm Up 1.43 5.79 0.24 0.16 1217.60 28.2 8.3 0.30 49.10 0.15 40.8 48.8 

Run 1 1.43 6.02 0.22 0.13 1232.73 28.6 8.2 0.00 49.89 0.00 48.8 48.8 

Run 2 1.40 5.91 0.20 0.13 1254.61 29.1 8.1 0.00 50.85 0.00 50.8 50.8 

AVE 1.41 5.97 0.21 0.130 1243.67 28.81 8.16 

UDDS 

Hybri

d 

22o

C 

COV (%) 2 1 7 2 1 1 1 

Table 7: Emissions and fuel consumption over the LA4 cycle 

 CO 

(g/mi) 

Nox 

(g/mi) 

HC 

(g/mi) 

PM 

(g/mi) 

CO2 

(g/mi) 

FC 

(L/100

km) 

FC 

(mpg) 

NEC/TCE 

(%) 

TCE 

(kWh) 

Battery 

NEC 

(kWh) 

SOC 

start 

(%) 

SOC 

end 

(%) 

Warm Up 1.70 7.63 0.29 na 1370.0 31.8 7.4 - - - - - 

Run 1 1.57 6.78 0.22 0.119 1334.2 30.9 7.6 - - - - - 

Run 2 1.53 7.30 0.22 0.108 1335.8 30.9 7.6 - - - - - 

AVE 1.55 7.04 0.22 0.113 1335.0 30.93 7.6 - - - - - 

LA4 

Conv. 

COV (%) 2 5 0 7 0 0 0 - - - - - 

Warm Up 1.55 7.55 0.25 na 1256.9 29.1 8.1 1.05 37.01 0.39 36.8 57.6 

Run 1 1.46 7.78 0.22 0.107 1243.6 28.8 8.2 0.25 33.54 0.08 53.6 58.0 

Run 2 1.37 7.84 0.21 0.102 1219.7 28.3 8.3 0.00 33.20 0.00 57.6 57.6 

Run 3 1.37 7.84 0.21 na 1219.7 28.3 8.3 0.00 32.88 0.00 57.6 57.6 

AVE 1.40 7.82 0.22 0.105 1227.7 28.44 8.27 

LA4 

Hybrid 

COV (%) 4 0 2 3 1 1 1 

20
Table 8: Emissions and fuel consumption over the UDDS at -7o

C 

 CO 

(g/mi) 

Nox 

(g/mi) 

HC 

(g/mi) 

PM 

(g/mi) 

CO2 

(g/mi) 

FC 

(L/100km) 

FC 

(mpg) 

NEC/TCE 

(%) 

TCE 

(kWh) 

Battery 

NEC 

(kWh) 

SOC 

start 

(%) 

SOC 

end 

(%) 

Warm Up 3.34 14.31 0.44 na 1604.72 37.2 6.3 - - - - - 

Run 1 1.96 6.59 0.29 0.098 1394.65 32.3 7.3 - - - - - 

Run 2 1.98 6.73 0.28 0.085 1383.46 32.1 7.3 - - - - - 

Run 3 1.98 6.35 0.27 0.085 1359.47 31.5 7.5 - - - - - 

AVE 1.98 6.56 0.28 0.089 1379.19 31.97 7.4 - - - - - 

UDDS 

Conventional 

-7o

C 

COV (%) 1 3 5 9 1 1 1 - - - - - 

Warm Up 2.36 6.92 0.52 na 1352.16 31.4 7.5 -0.04 55.89 -0.02 50.8 49.6 

Run 1 1.55 6.74 0.26 0.09 1249.89 29.0 8.1 0.09 50.78 0.04 49.6 52.0 

Run 2 1.61 6.64 0.26 0.08 1217.17 28.2 8.3 -0.06 49.34 -0.03 51.6 50.0 

AVE 1.58 6.69 0.26 0.084 1233.53 28.59 8.23 

UDDS Hybrid 

-7o

C 

COV (%) 3 1 0 9 2 2 2 

Table 9: Emissions and fuel consumption with 10% reduction in road load over the UDDS 

 CO 

(g/mi) 

Nox 

(g/mi) 

HC 

(g/mi) 

PM 

(g/mi) 

CO2 

(g/mi) 

FC 

(L/100km) 

FC 

(mpg) 

NEC/TCE 

(%) 

TCE 

(kWh) 

Battery 

NEC 

(kWh) 

SOC 

start 

(%) 

SOC 

end 

(%) 

Warm Up 1.39 5.90 0.23 0.115 1130.66 26.2 9.0 -0.44 46.09 -0.20 57.6 46.8 

Run 1 1.40 5.94 0.22 0.102 1124.90 26.1 9.0 0.13 45.77 0.06 46.8 50.0 

Run 2 1.41 5.79 0.22 0.098 1133.01 26.3 9.0 -0.06 46.10 -0.03 49.6 48.0 

AVE 1.40 5.87 0.22 0.100 1128.96 26.16 8.99 

Hybrid 

10% 

reduced 

load 

COV (%) 1 2 1 3 1 1 1 

21
0

5

10

15

20

25

30

35

CILCC UDDS LA4

Fuel Consumption (L/100km)

Conventional Hybrid

Hybrid Reduced Road Load Conventional -7C

Hybrid -7C

NA NA NA NA

Figure 14: Average fuel consumption ± 1 standard deviation on CILCC, UDDS, and LA4 

drive cycles 

0

0.5

1

1.5

2

2.5

3

CILCC UDDS LA4

Emission Rate (g/mi)

Conventional Hybrid

Hybrid Reduced Road Load Conventional -7C

Hybrid -7C

NA NA NA NA

Figure 15: Average CO emission rate ± 1 standard deviation on CILCC, UDDS, and LA4 

drive cycles 

22
0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

CILCC UDDS LA4

Emission Rate (g/mi)

Conventional Hybrid

Hybrid Reduced Road Load Conventional -7C

Hybrid -7C

NA NA NA NA

Figure 16: Average HC emission rate ± 1 standard deviation on CILCC, UDDS, and LA4 

drive cycles 

0

1

2

3

4

5

6

7

8

9

CILCC UDDS LA4

Emission Rate (g/mi)

Conventional Hybrid

Hybrid Reduced Road Load Conventional -7C

Hybrid -7C

NA NA NA NA

Figure 17: Average NOx emission rate ± 1 standard deviation on CILCC, UDDS, and LA4 

drive cycles 

23
0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

CILCC UDDS LA4

Emission Rate (g/mi)

Conventional Hybrid

Hybrid Reduced Road Load Conventional -7C

Hybrid -7C

NA NA NA NA

Figure 18: Average PM emission rate ± 1 standard deviation on CILCC, UDDS, and LA4 

drive cycles 

6.3 Duty cycle and idle results 

Emission rates and fuel consumption results for Duty Cycles A and B, as well as 

the 10 minute idle tests, are shown in the following tables. During the duty load 

cycles, the hybrid battery regularly depleted to approximately 22% SOC as 

electrical energy was used to operate the hydraulic lift arm. Once the SOC 

reached this lower limit, the engine turned on and the battery was charged to 

approximately 69% SOC. As a result of this large swing in SOC, the battery NEC 

for the duty load cycle was as high as 3.4% of the total cycle energy. SOC 

corrections were performed according to SAEJ2711, and the linear “best fits” are 

plotted in Figures 20-25. The corrected values are presented in the tables below, 

except in cases where the coefficient of determination (R2) was less than 0.8. 

This was the case for the CO and PM emission rates on each duty cycle. It is 

interesting to note that both THC and NOx emission rates appear to increase 

with greater electrical energy use. Unfortunately, of the three Duty Cycle A 

repeats and three Duty Cycle B repeats, only one test ended with a negative 

battery NEC (battery depletion). Both negative and positive battery NEC results 

are required for linear interpolation (as opposed to extrapolation) of the zero net 

energy change result. In future, because interpolated data is generally more 

robust than extrapolated data, greater care should be taken to ensure both 

negative and positive NEC on the duty cycle repeats. 

24
Considering that the net energy change was not always well correlated to the 

emission rate, and that sometimes trends were not as expected, it may not 

always be appropriate to assume a linear relationship between emission rate and 

net energy change. While higher fuel consumption may contribute to a higher 

emission rate, other factors such as temperatures of engine and emission control 

technologies, and efficient operation of the engine will also play a role. While 

hybrid systems may reduce emissions through reduced fuel consumption, 

emissions may increase due to other factors, and the relationship may not 

always be linear. In such cases, the coefficient of determination may be low and 

the SOC correction is not possible. 

Table 10: Emissions and Fuel Consumption over Duty Cycle A 

 CO 

(g/hr) 

Nox 

(g/hr) 

HC 

(g/hr) 

PM 

(g/hr) 

CO2 

(g/hr) 

FC 

(kg/h) 

NEC/ 

TCE (%) 

TCE 

(kWh) 

Battery 

NEC 

(kWh) 

SOC 

start 

SOC 

end 

Run 1 40.40 103.70 1.88 0.37 9606.88 3.046 - - - - - 

Run 2 38.62 111.46 4.46 0.40 9481.94 3.009 - - - - - 

Run 3 38.58 110.20 5.40 0.54 9384.02 2.979 - - - - - 

AVE 39.2 108.45 3.91 0.44 9490.95 3.01 - - - - - 

Conventional 

COV (%) 3 4 47 21 1 1 - - - - - 

Run 1 7.04 16.28 1.26 0.00 2226.52 0.706 -0.16 4.59 -0.01 24.4 24.0 

Run 2 7.04 14.16 0.50 0.00 2466.68 0.781 2.84 4.74 0.13 60.8 68.0 

Run 3 7.24 15.16 0.76 0.00 2610.32 0.826 2.67 4.77 0.13 58.0 64.8 

AVE 7.11b 16.2a 1.23a 0.00b 2247.4a 0.71a

Hybrid 

COV (%) 2 7 46 8 8 8 

a

corrected emission rate, bcorrection required but not possible 

Table 11: Emissions and Fuel Consumption over Duty Cycle B 

 CO 

(g/hr) 

Nox 

(g/hr) 

HC 

(g/hr) 

PM 

(g/hr) 

CO2 

(g/hr) 

FC 

(kg/h) 

NEC/TCE 

(%) 

TCE 

(kWh) 

Battery 

NEC 

(kWh) 

SOC 

start SOC end 

Run 1 38.42 91.92 5.88 0.50 8883.60 2.822 - - - - - 

Run 2 37.90 91.56 5.88 0.72 8795.22 2.794 - - - - - 

Run 3 37.58 93.32 5.82 0.86 9122.54 2.896 - - - - - 

AVE 37.97 92.27 5.86 0.69 8933.79 2.84 - - - - - 

Conventional 

COV (%) 1 1 1 26 2 2 - - - - - 

Run 1 6.40 24.96 1.22 0.00 2128.34 0.674 1.22 4.90 0.06 63.6 66.8 

Run 2 6.34 19.00 0.92 0.00 2464.46 0.780 3.10 4.83 0.15 58.0 66.0 

Run 3 6.50 16.34 0.94 0.00 2472.66 0.783 3.43 4.80 0.16 34.0 42.8 

AVE 6.41b 29.67a 1.39a 0.00b 1925.4a 0.61a

Hybrid 

COV (%) 1 22 16 7 8 8 

a

corrected emission rate, bcorrection required but not possible 

25
Table 12: Emissions and fuel consumption during a 10 minute idle 

 Temp CO (g/hr) Nox(g/hr) HC 

(g/hr) 

PM 

(g/hr) 

CO2 

(g/hr) 

FC 

(L/hr) 

FC 

(kg/h) 

NEC/ 

TCE 

(%) 

TCE 

(kWh) 

Battery 

NEC 

(kWh) 

SOC 

start 

SO

C 

en

d 

Conv. 22C 17.65 114.12 0.97 0.283 6060.72 2.266 1.918 - - - - - 

Hybrid 22C 18.83 93.94 1.61 0.000 5095.03 1.908 1.615 0.00 3.18 0.00 38.0 38.

0 

Conv. -7C 40.23 85.16 2.70 0.682 5016.93 1.893 1.602 - - - - - 

Hybrid -7C 45.64 68.98 3.99 0.001 4340.25 1.646 1.393 0.00 2.74 0.00 38.8 38.

8 

Duty Cycles and Idle

0

2

4

6

8

10

12

CO/10 Nox/10 HC PM Fuel

Consumption

emission rate [g/hr]

fuel consumption [kg/hr]

Duty A Conv.

Duty B Conv.

Idle Conv.

Idle Conv. -7C

Duty A Hybrid

Duty B Hybrid

Idle Hybrid

Figure 19: Duty cycle and idle results, SOC corrected as necessary 

26
Duty Cycle Fuel Consumption Correction

y = 0.0007x + 0.7122

R2

 = 0.8255

y = 0.0011x + 0.6107

R2

 = 0.9878

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

-50 0 50 100 150 200

NEC (Wh)

Fuel Consumption (kg/hr)

Duty A FC

Duty B FC

Linear (Duty A FC)

Linear (Duty B FC)

Figure 20: Duty cycle fuel consumption correction 

Duty CO2 Consumption Correction

y = 2.2076x + 2247.4

R2

 = 0.8291

y = 3.4473x + 1925.4

R2

 = 0.9876

0

500

1000

1500

2000

2500

3000

-50 0 50 100 150 200

NEC (Wh)

Emission Rate (g/hr)

Duty A CO2

Duty B CO2

Linear (Duty A CO2)

Linear (Duty B CO2)

Figure 21: Duty cycle CO2 emission rate correction 

27
Duty Cycle CO Correction

y = 0.0007x + 7.0505

R2

 = 0.2106

y = 0.0004x + 6.3649

R2

 = 0.0742

6.20

6.30

6.40

6.50

6.60

6.70

6.80

6.90

7.00

7.10

7.20

7.30

-50 0 50 100 150 200

NEC (Wh)

Emission Rate (g/hr)

Duty A CO

Duty B CO

Linear (Duty A CO)

Linear (Duty B CO)

Figure 22: Duty cycle CO emission rate correction 

Duty Cycle THC Correction

y = -0.0046x + 1.2315

R2

 = 0.9146

y = -0.0029x + 1.3891

R2

 = 0.9635

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

-50 0 50 100 150 200

NEC (Wh)

Emission Rate (g/hr)

Duty A HC

Duty B HC

Linear (Duty A HC)

Linear (Duty B HC)

Figure 23: Duty cycle HC emission rate correction 

28
Duty Cycle NOx Correction

y = -0.012x + 16.215

R2

 = 0.8154

y = -0.0768x + 29.67

R2

 = 0.9702

0.00

5.00

10.00

15.00

20.00

25.00

30.00

-50 0 50 100 150 200

NEC (Wh)

Emission Rate (g/hr)

Duty A NOx

Duty B NOx

Linear (Duty A NOx)

Linear (Duty B NOx)

Figure 24: Duty cycle NOx emission rate correction 

Duty Cycle PM Correction

y = -1E-07x + 0.0002

R2

 = 0.4245

y = -1E-07x + 0.0002

R2

 = 0.3172

0.0E+00

2.0E-05

4.0E-05

6.0E-05

8.0E-05

1.0E-04

1.2E-04

1.4E-04

1.6E-04

1.8E-04

2.0E-04

-50 0 50 100 150 200

NEC (Wh)

Emission Rate (g/hr)

Duty A PM

Duty B PM

Linear (Duty A PM)

Linear (Duty B PM)

Figure 25: Duty cycle PM emission rate correction 

29
6.4 Sample Size Calculation and Statistics 

The criterion for determining that a vehicle meets the SmartWay performancebased designation is an 80% probability that the results exceed the fuel efficiency 

designation by an amount equal to the lower tail of the 95% confidence interval of 

the test measurements. Where low emission reductions / fuel efficiency 

improvements are expected and/or measurements have high variability, more 

test repeats will be required. 

Appendix I of the SmartWay test protocol draft gives a method for calculating an 

appropriate sample size for detection of a specified emission reduction or fuel 

efficiency improvement. The sample size requirement is highly dependent on the 

variability in the data. The coefficients of variance (COVs) obtained in this study 

over repeats of each test condition are summarized in Table 13. When an SOC 

correction was performed and the coefficient of determination was greater than 

0.8, COVs were calculated using the standard error determined from the 

regression analysis. These are shown in bold. When the overall pollutant 

emission rate was low, as was the case for PM and HC on some cycles, the 

relative uncertainty in the measurement was increased, resulting in a higher 

COV. 

Table 13: Coefficients of variance (%) summary 

CO NOx HC PM CO2 FC FE 

CILCC 2 5 19 5 2 2 2 

UDDS 2 3 6 8 1 1 1 

LA4 2 5 0 7 0 0 0 

UDDS Cold 1 3 5 9 1 1 1 

Duty A 3 4 47 21 1 1 na 

Conv. 

Duty B 1 1 1 26 2 2 na 

CILCC 2 2 3 9 1 1 1 

UDDS 2 1 7 2 1 1 1 

LA4 4 0 2 3 1 1 1 

UDDS Cold 3 1 0 9 2 2 2 

Duty A 2 7 31 8 8 8 na 

Hybrid 

Duty B 1 15 13 7 4 4 na 

Given the actual coefficients of variance observed in this test program, the 

minimum emission reductions and fuel efficiency improvements that could be 

detected using three test repeats are given in Table 15. This table will be useful 

in designing test plans, assuming future COVs are similar to those observed in 

this study. Where an emission reduction or fuel efficiency improvement is 

expected to be lower than the table value, it would be wise to plan to conduct 

more test repeats to ensure statistical significance. For instance, if a technology 

is expected to reduce the HC emission rate by less than 25% on the CILCC, 

more than three test repeats will be needed in order to detect the reduction with 

the desired confidence level. 

30
Table 14: Minimum reductions and improvements with 80% probability of detection at the 

95% confidence level using 3 repeats 

Minimum reduction detectable (%) 

Minimum 

improvement 

detectable 

(%) 

CO NOx HC PM CO2 FC FE 

CILCC 6 9 25 18 5 5 5 

UDDS 5 6 15 12 4 4 4 

LA4 9 9 4 12 2 2 2 

UDDS Cold 5 6 8 20 4 4 4 

Duty A 6 14 62 29 14 14 na 

Duty B 3 37 22 33 8 8 na 

6.5 Fuel Efficiency Improvements and Emission Reductions 

Fuel efficiency improvements and emission reductions (Table 16, Figures 26-30) 

provided by the hybrid power train were most pronounced during the duty load 

cycles. Emissions of CO, CO2, NOx, and HC were reduced by 74 to 100 % and 

fuel consumption was reduced by 74%. This reduction is lower than the 87% and 

91% improvements reported by SwRI [3]. It should be noted that, as described in 

Section 6.1, the load vs. time schedule was not followed precisely. The auxiliary 

hydraulic circuit used by SwRI was able to follow the schedule more accurately. 

Fuel efficiency improvements and emission reductions were less distinct on the 

driving cycles. Of the driving cycles, the CILCC provided for the greatest fuel 

efficiency improvement, with the hybrid showing a fuel efficiency increase of 13% 

over the conventional truck. Again, this is lower than the improvement observed 

in the SwRI study [3]. On the UDDS and LA4 cycles, fuel efficiency 

improvements were 8% and 10% respectively. 

Emission reductions on the driving cycles were varied, and in fact, the hybrid 

often showed emission increases over the conventional truck. These are shown 

in the tables below in bold red type as negative reductions. It is important to note 

that in almost all cases where the hybrid system appeared to cause emission 

increases, the increase was insignificant. This is best illustrated in Figures 26 to 

30, which show the fuel efficiency improvements and emission reductions 

bracketed by upper and lower bounds of the 90% confidence interval, based on a 

two-tailed t-test. Negative emission reductions almost always have a confidence 

interval that crosses zero (no impact of hybrid system). Exceptions are the THC 

and PM emission rates over the CILCC, where the hybrid system did cause an 

increased emission rate. 

31
Table 16 gives the lower bound of the 95% confidence interval based on a onetailed t-test as described in Appendix J of the draft SmartWay test protocol. 

The final rows in Table 16 and 17 are not a comparison between conventional 

and hybrid systems, but between UDDS tests on the hybrid truck with the 

appropriate road load settings, and with a 10% reduced road load. When road 

load was reduced by 10%, fuel efficiency was improved by 10%. The change in 

road load had essentially no impact on the emission rates of CO, NOx and HC. 

The PM emission rate, however, was reduced by 23% due to the lower road 

load. 

Table 15: Emission reductions and fuel efficiency improvements 

Emission and Fuel Consumption Reductions 

Fuel 

Efficiency 

Improvement 

Cycle CO NOx HC PM CO2 FC FE 

CILCC 0.17 0.23 -0.34 -0.35 0.12 0.12 0.13 

UDDS 0.07 0.11 -0.13 -0.03 0.07 0.07 0.08 

LA4 0.10 -0.11 0.01 0.08 0.08 0.08 0.09 

Duty A 0.82 0.86 0.84 1.00 0.74 0.74 na 

Duty B 0.83 0.78 0.82 1.00 0.74 0.74 na 

UDDS -7degC 0.20 -0.02 0.09 0.05 0.11 0.11 0.12 

Hybrid with 10% Road Load 

Reduction 0.00 0.02 -0.08 0.23 0.09 0.09 0.10 

Table 16: Lower bound of the 95% confidence interval on emission reductions and fuel 

efficiency improvements 

Emission and Fuel Consumption Reductions 

Fuel 

Efficiency 

Improvement 

Cycle CO NOx HC PM CO2 FC FE 

CILCC 0.14 0.18 -0.56 -0.53 0.08 0.08 0.10 

UDDS 0.04 0.06 -0.31 -0.17 0.05 0.05 0.04 

LA4 0.04 -0.32 -0.03 -0.24 0.06 0.06 0.07 

Duty A 0.81 0.85 0.76 1.00 0.71 0.71 na 

Duty B 0.81 0.73 0.79 1.00 0.73 0.73 na 

UDDS -7degC 0.11 -0.06 0.01 -0.18 0.07 0.07 0.01 

Hybrid with 10% Road Load 

Reduction -0.07 -0.03 -0.36 0.18 0.04 0.04 0.04 

32
Fuel Efficiency Improvement

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Fuel Efficiency Improvement Ratio

CILCC UDDS LA4 Duty B Duty A UDDS 

-7degC

-10% 

load

Figure 26: Fuel efficiency improvement with 90% confidence interval 

CO Emission Rate Reduction

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Emission Reduction Ratio

CILCC UDDS LA4 Duty B Duty A UDDS 

-7degC

-10% 

load

Figure 27: Reduction in CO emission rate with 90% confidence interval 

33
THC Emission Rate Reduction

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Emission Reduction Ratio

CILCC UDDS LA4 Duty B Duty A UDDS 

-7degC

-10% 

load

Figure 28: Reduction in THC emission rate with 90% confidence interval 

NOx Emission Rate Reduction

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Emission Reduction Ratio

CILCC UDDS LA4 Duty B Duty A UDDS 

-7degC

-10% 

load

Figure 29: Reduction in NOx emission rate with 90% confidence interval 

34
PM Emission Rate Reduction

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Emission Reduction Ratio

CILCC UDDS LA4 Duty B Duty A UDDS 

-7degC

-10% 

load

Figure 30: Reduction in PM emission rate with 90% confidence interval 

6.6 Cold Temperature Impacts 

Cold temperature impacts were examined over the heavy duty UDDS. Tests 

were performed at 22oC and -7oC, and all tests were preceded by a warm-up HD 

UDDS. The effects are displayed in Figure 31. The cold ambient temperature 

had no significant impact on fuel consumption or CO2 emission rate after warmup. There were, however, significant effects on pollutant emission rates. At cold 

ambient temperature the CO emission rate increased by 30% for the 

conventional truck, and by 12% for the hybrid truck. The THC emission rate 

increased by 54% for the conventional truck, and by 24% for the hybrid truck. 

The NOx emission rate increased by 12% for the hybrid, but showed no change 

for the conventional vehicle. The PM emission rate was decreased at cold 

ambient temperature relative to standard temperature. It should be noted that 

with only two UDDS test repeats on the hybrid at each temperature, the 90% 

confidence intervals on the THC and PM emission rates were particularly wide. 

More repeats are needed in future. 

35
Emission Increases at -7o

C Ambient Temperature

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

Emission Increase

Conventional

Hybrid

CO NOx THC PM CO2

Figure 31: Cold temperature impacts on pollutant emission rates (with 90% confidence 

interval) 

7.0 CONCLUSIONS AND RECOMMENDATIONS 

Benefits of Hybrid Technology

Benefits of adopting this hybrid system, based on tests conducted according to 

the proposed SmartWay test protocol, include: 

During CILCC driving; 

(1) a fuel efficiency improvement of 13 ± 3% 

(2) a CO2 emission rate reduction of 12 ± 4% 

(3) a NOx emission rate reduction of 23 ± 5% 

(4) a CO emission rate reduction of 17 ± 3% 

and during hydraulic loading; 

(1) a fuel consumption reduction of 74 ± 3% (duty A) and 74 ± 2% (duty B) 

(2) a CO2 emission rate reduction of 74 ± 3% (duty A) and 74 ± 2% (duty B) 

(3) a NOx emission rate reduction of 86 ± 1% (duty A) and 78 ± 6% (duty B) 

(4) a CO emission rate reduction of 82 ± 1% (duty A) and 83 ± 1% (duty B) 

(5) a THC emission rate reduction of 84 ± 9% (duty A) and 82 ± 4% (duty B) 

(6) a PM emission rate reduction of 100% 

Clearly, the benefits of hybrid technology are considerable, and of greatest 

magnitude during hydraulic loading duty operation. There were, however, several 

36
instances where the hybrid technology showed a disadvantage relative to the 

conventional system. The hybrid system caused THC and PM emission rates to 

increase during driving by 34% ± 22% and 35% ± 18% respectively. It is 

important to note that emission rates are dependent not only on the amount of 

fuel consumed, but on the engine temperature and operation of after-treatment 

technologies. In future, more test repeats should be used to reduce the width of 

the confidence interval on THC and PM emission rates. 

While the CILCC is currently the recommended test cycle of the proposed 

SmartWay Test Protocol, other drive cycles may yield significantly different 

results. For example, the fuel efficiency improvement on the UDDS was 8% ± 

4%, and on the LA4 it was 10% ± 2%. These improvements are less substantial 

than those of the CILCC. 

Test to test variability and statistics

A table of coefficients of variance was presented in Section 6.4. These COVs can 

be used to determine the required number of driving test repeats for a given 

expected fuel efficiency improvement and emission reduction. The net electrical 

energy changes on the drive cycles were within the SAE J2711 tolerance, and 

thus corrections were not required. 

Unlike for the drive cycles, the net electrical energy changes were highly 

elevated on the duty cycles as the battery charged to approximately 69% and 

depleted to 22%. For cycles with these high net energy changes, where SOC 

correction is required, the standard error on the reported value must be 

determined from regression analysis. It is recommended that such a method be 

described in the statistics section of the SmartWay Protocol. 

Typical CO2 Consumption Rate

The CO2 emission rates of both conventional and hybrid trucks under the various 

driving conditions are given in Table 17. 

 Table 17: CO2 Emission Rate Summary 

CILCC 

(g/mi) 

HD 

UDDS 

(g/mi) 

LA4 

(g/mi) 

HD 

UDDS 

-7degC 

(g/mi) 

Duty A 

(g/hr) 

Duty B 

(g/hr) 

Conventional 1212 1343 1335 1379 9491 8934 

Hybrid 1068 1244 1228 1234 2247a 1925a

 a SOC corrected 

These emission rates can be used to help characterize the typical CO2 emission 

rates of conventional and hybrid utility trucks. 

Cold Temperature Impacts

Because all tests were performed after a warm-up cycle, the -7o

C ambient 

temperature had little effect on fuel efficiency. There were, however, substantial 

37
impacts on emission rates of CO, and NOx. More repeats are needed in future to 

reduce the width of the confidence interval on THC and PM emission impacts. 

Road Load Impacts

When road load was reduced by 10%, fuel efficiency was improved by 10%. The 

change in road load did not have a significant impact on the emission rates of 

CO, NOx and HC. The PM emission rate, however, was reduced by 23% due to 

the lower road load. This result offers insight into the consequences of any 

inaccuracies in the coast down procedure. 

Recommendations

It is recommended that the following changes/additions be made to the 

SmartWay Test Protocol: 

(1) Considering the varying results obtained under different driving conditions, 

care should be taken when selecting the drive cycle to ensure it is 

representative of real world operation. Because the CILCC is 53 minutes 

long and repetitive, it is difficult for one driver to perform the minimum 4 

repeats (warm-up/practice + 3 repeats). It is the ERMS’s recommendation 

that the cycle be used for dynamometer testing only until better data 

(perhaps from real world logging of vehicle operation) becomes available. 

(2) Indicate specifically that augmented braking should be disabled for 

dynamometer testing of hybrid vehicles. 

(3) When testing on a two-wheel (single roll) dynamometer, ABS fault codes 

should be disabled. 

(4) A note addressing the use of regression analysis to determine standard 

error when SOC correction is required should be added to the statistical 

methods proposed in the protocol. 

During the second round of testing, it is recommended that the following changes 

be made to the program: 

(1) Minimum of three repeats always in order to reduce the width of the 

confidence interval 

(2) Direct measurement of current (and possibly voltage) from the hybrid 

battery in order to verify the SOC readings from the J1939 device. 

(3) Reduced temperature of -18o

C to investigate sensitivity of emissions and 

fuel consumption to cold climate 

(4) On-road coast down data with resolution of 0.1 mph, and all coast downs 

to a speed less then 5.0 mph if possible. 

Additional changes to the program may be made upon recommendation by the 

U.S. EPA. 

REFERENCES 

[1] United States Environmental Protection Agency, “SmartWay Fuel 

Efficiency Test Protocol for Medium and Heavy Duty Vehicles, Working 

Draft”, EPA420-P-07-003. (November 2007). 

38
[2] Society of Automotive Engineers, “Recommended practice for measuring 

fuel economy and emissions of hybrid-electric and conventional heavyduty vehicles” Surface Vehicle Recommended Practice No. SAE - J2711, 

(2002). 

[3] Southwest Research Institute, “Emissions and Fuel Economy Testing of 

Three Utility Trucks”, SwRI Project No. 03.11602, (2007). 

39
Appendix A – Vehicle Specifications 

Table A-1: Conventional Utility Truck 

ITEM DATA

ERMS Vehicle ID#: ER2008-038 

VEHICLE VIN 1HTMMAAL67H320541 

VEHICLE TYPE Utility Truck 

VEHICLE MANUF AND MAKE International 

VEHICLE MODEL 4300SBA 4X2 

NUMBER OF AXLES 2 (1 Front, 1 Rear) 

NUMBER OF DRIVE AXLES 1 (Rear) 

TRANS TYPE AND # OF GEARS Alison 5-Speed Automatic Transmission 

VEHICLE BUILD DATE Jan. 9, 2006 

GVWR 25,999 

EXHAUST PIPE DIAMETER 4” 

STARTING ODOMETER 14,200 

ENGINE FAMILY ON LABEL 6NVXH0466AEA 

ENGINE MANUFACTURER Navistar 

ENGINE MODEL D210 

SERIAL NUMBER 466MM2U2101062 

ENGINE BUILD DATE n/a 

HP RATING ON LABEL 210 

RATED SPEED 2300 

TORQUE RATING 520 

TORQUE SPEED 1400 

EMISSION CONTROLS Electronic Injection, EGR, Oxidation Catalyst 

MAKE AND DESCRIPTION OF BODY Altec L42A Aerial Boom 

OTHER BODY INFORMATION Boom Platform Capacity - 400 lbs 

OTHER BODY INFORMATION Boom Platform Height - 42 ft 

OTHER BODY INFORMATION Max. Hydraulic System Pressure Setting - 3000 PSI

OTHER BODY INFORMATION Throttle Controls - High Idle, Low Idle 

AMOUNT OF PAYLOAD n/a 

TOTAL WEIGHT OF VEHICLE AND BODY 20,242 

FUEL DESCRIPTION ULSD 

VEHICLE SPEED GOVERNED Yes, 65 MPH 

Tire Tread Depth (measured from outside --> in) 

 Section 1 Left Front 11, 14, 11 

 Right Front 10, 11, 12 

 Left Rear 12, 11, 15, 14, 13, 12 

 Right Rear 11, 10, 12, 12, 11, 10 

 Section 2 Left Front 14, 12, 15 

 Right Front 14, 11, 12 

 Left Rear 12, 11, 12, 13, 13, 11 

 Right Rear 11, 10, 14, 12, 10, 9 

 Section 3 Left Front 11, 11, 11 

 Right Front 14, 11, 12 

 Left Rear 11, 11, 14, 13, 12, 10 

 Right Rear 11, 11, 12, 12, 12, 11 

40
Table A-2: Hybrid Utility Truck 

ITEM DATA

ERMS Vehicle ID#: ER2008-039 

VEHICLE VIN 1HTMMAANX6H152743 

VEHICLE TYPE Utility Truck 

VEHICLE MANUF AND MAKE International 

VEHICLE MODEL 4300SBA 4X2 

NUMBER OF AXLES 2 (1 Front, 1 Rear) 

NUMBER OF DRIVE AXLES 1 (Rear) 

TRANS TYPE AND # OF GEARS Fuller 6-Speed Automated Manual Transmission 

VEHICLE BUILD DATE Apr. 19, 2005 

GVWR 25,999 

EXHAUST PIPE DIAMETER 4” 

STARTING ODOMETER 23,738 

ENGINE FAMILY ON LABEL 5NVXH0466AEA 

ENGINE MANUFACTURER Navistar 

ENGINE MODEL D225CFF 

SERIAL NUMBER 1858217C1 

ENGINE BUILD DATE n/a 

HP RATING ON LABEL 225 

RATED SPEED 2300 

TORQUE RATING 560 

TORQUE SPEED 1400 

EMISSION CONTROLS Electronic Injection, EGR, Oxidation Catalyst 

MAKE AND DESCRIPTION OF BODY Altec L42A Aerial Boom 

OTHER BODY INFORMATION Boom Platform Capacity - 300 lbs 

OTHER BODY INFORMATION Boom Platform Height - 42 ft 

OTHER BODY INFORMATION Max. Hydraulic System Pressure Setting - 3000 PSI

OTHER BODY INFORMATION Throttle Controls - High Idle, Electric PTO 

AMOUNT OF PAYLOAD n/a 

TOTAL WEIGHT OF VEHICLE AND BODY 23,062 

FUEL DESCRIPTION ULSD 

VEHICLE SPEED GOVERNED Yes, 65 MPH 

Tire Tread Depth (measured from outside --> in) 

 Section 1 Left Front 15, 17, 15 

 Right Front 15, 14, 16 

 Left Rear 14, 12, 14, 15, 14, 15 

 Right Rear 8, 9, 10, 6, 5, 6 

 Section 2 Left Front 18, 16, 17 

 Right Front 19, 14, 19 

 Left Rear 14, 13, 13, 15, 15, 13 

 Right Rear 12, 10, 12, 5, 6, 6 

 Section 3 Left Front 19, 18, 19 

 Right Front 14, 14, 18 

 Left Rear 13, 13, 14, 15, 15, 14 

 Right Rear 11, 10, 12, 6, 6, 5 

Vehicle Vendor Contact Claude Masters (561-722-2776) 

Hybrid Drive Train Manufacturer Eaton Corporation 

Type of RESS 340 V DC NiMH Battery 

Regenerative Braking Electric Motor / Generator via Driveshaft 

Special features Hydraulic Boom Arm 

41