Technical Report

NREL/TP-540-44134

December 2009

Twelve-Month Evaluation of 

UPS Diesel Hybrid Electric 

Delivery Vans

M. Lammert
National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393

303-275-3000 • www.nrel.gov

NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency and Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

Contract No. DE-AC36-08-GO28308

Technical Report

NREL/TP-540-44134

December 2009

Twelve-Month Evaluation of 

UPS Diesel Hybrid Electric 

Delivery Vans

M. Lammert

Prepared under Task No. FC08.3000
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. 

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infringe privately owned rights. Reference herein to any specific commercial product, process, or service by 

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recommendation, or favoring by the United States government or any agency thereof. The views and 

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i

Acknowledgments

This evaluation is funded through the Advanced Vehicle Testing Activity, which is managed by 

Lee Slezak within the U.S. Department of Energy (DOE) Office of Energy Efficiency and 

Renewable Energy. All publications regarding the United Parcel Service (UPS) hybrid delivery 

van evaluation will be posted on DOE’s Energy Efficiency and Renewable Energy Web site. See 

the Medium- and Heavy-Duty Vehicles section at the following link: 

http://www1.eere.energy.gov/vehiclesandfuels/avta/index.html. 

This evaluation, conducted at UPS, would not have been possible without the support and 

cooperation of many people. The author wishes to thank each of the following:

U.S. Department of Energy

Lee Slezak

UPS

Robert K. Hall

Bill Brentar

Eaton Corporation

Alex Stuckey
ii

List of Acronyms and Abbreviations

AVTA Advanced Vehicle Testing Activity

bhp brake horsepower

CO carbon monoxide

CO2 carbon dioxide

DOE U.S. Department of Energy

EGR exhaust gas recirculation

FT&E Fleet Test and Evaluation (NREL team) 

g/bhp-hr grams per brake horsepower hour

GPS global positioning system

GVWR gross vehicle weight rating

HC hydrocarbon

HVAC heating, ventilation, and air conditioning 

mpg miles per gallon

mph miles per hour

MY model year

NOx oxides of nitrogen

NREL National Renewable Energy Laboratory

PM particulate matter

ppm parts per million

ReFUEL Renewable Fuels and Lubricants (Laboratory)

rpm revolutions per minute 

THC total hydrocarbons

ULSD ultra-low-sulfur diesel

UPS United Parcel Service

VDC voltage direct current
iii

Executive Summary 

This 12-month evaluation is part of a series of evaluations from the U.S. Department of 

Energy (DOE). Using an established and documented evaluation protocol, DOE—

through the National Renewable Energy Laboratory (NREL)—has been tracking and 

evaluating new propulsion systems in transit buses and trucks for more than 10 years. 

The DOE/NREL vehicle evaluations are a part of the Advanced Vehicle Testing Activity 

(AVTA), which supports DOE’s Vehicle Technologies Program.

The role of AVTA is to bridge the gap between research and development and the 

commercial availability of advanced vehicle technologies that reduce petroleum use in 

the United States and improve air quality. The main objective of AVTA projects is to 

provide comprehensive, unbiased evaluations of advanced vehicle technologies in 

commercial use. Data are collected and analyzed for operation, maintenance, 

performance, costs, and emissions characteristics of both advanced-technology fleets and 

comparable conventional-technology fleets that are operating at the same site. AVTA 

evaluations enable fleet owners and operators to make informed vehicle-purchasing 

decisions.

This report focuses on a parallel hybrid-electric diesel delivery van propulsion system 

currently being operated by United Parcel Service (UPS). The propulsion system is an 

alternative to the standard diesel system and could enable reductions in emissions, 

primarily particulate matter and oxides of nitrogen (NOx), as well as reductions in 

petroleum use. Hybrid propulsion allows for increased fuel economy, which ultimately 

reduces petroleum use.

Evaluation Design

This 12-month evaluation used six P70H hybrids and six P70D standard diesels that are 

located in two UPS facilities in the Phoenix, Arizona, area. Dispatch and maintenance 

practices are the same at both facilities. GPS logging, fueling, and maintenance records 

are used to evaluate the performance of these hybrid step delivery vans.

In addition, a P100H hybrid and a P100D standard diesel were tested at NREL’s 

Renewable Fuels and Lubricants (ReFUEL) Research Laboratory. Testing was performed 

over multiple standard drive cycles—the Combined International Local and Commuter 

Cycle, the West Virginia University City cycle, and the Central Business District cycle—

to evaluate the fuel economy and emissions benefits gained through hybridization. The 

P100 chassis and engine combination is different from the one used in the P70 and has a 

higher gross vehicle weight (GVW), but it uses the same hybrid system as the P70’s.

Evaluation Results

The results and related discussions included here focus only on the selected facilities, the 

two P70 study groups, and the two P100 vehicles tested at the ReFUEL lab.

Delivery Van Use and Duty Cycle

The hybrids had an average monthly mileage rate that was 20% less than that of the 

diesel vans. The hybrids consistently were driven a fewer number of miles throughout the 
iv

evaluation period, but they also experienced extended downtime late in the year as a 

result of an accident and calibration issues. The hybrids spent more time idling and 

operating at slower speeds than the diesels did, and the diesels spent slightly more time 

operating at greater speeds; this accounted for much of the hybrids’ fewer monthly miles.

Fuel Economy

The 12-month average fuel economy for the hybrid vans is 13.1 mpg, 28.9% greater than 

the diesel van group’s 10.2 mpg. Figure ES-1 shows the average monthly miles per 

gallon for each van group and the cumulative average miles per gallon, as well.

Figure ES-1. Average monthly and cumulative fuel economy

Maintenance Costs

The total maintenance cost per mile of $0.140 for the hybrid vans was 8% less than the 

$0.152 for the diesel vans. The propulsion-related maintenance cost per mile of $0.034 

for the hybrid vans was 5% less than the $0.036 for the diesel vans. Using a t-test, 

researchers found neither difference to be statistically significant.

Reliability

The hybrid group had a cumulative average of 95.5% uptime over the 12-month study 

period, less than the diesel group’s cumulative average of 99.3% uptime. The hybrids 

experienced troubleshooting and recalibration issues related to prototype components that 

are primarily responsible for the lower uptime figures.

Laboratory Fuel Economy and Emissions Testing

The P100 hybrid vans consistently showed a 31%-37% fuel economy improvement over 

the conventional P100 vans on the three tested duty cycles. The hybrid vans showed 

improvement in some emissions, but the results varied significantly depending on the 

cycle being run. The hybrid vans showed an increase in NOx for all cycles. 

UPS Fuel Economy Comparison

Monthly Average and Cummulative

8

10

12

14

16

Jan

08

Feb

08

Mar

08

Apr

08

May

08

Jun

08

Jul 08 Aug

08

Sep

08

Oct

08

Nov

08

Dec

08

Miles per gallon

Diesel group Hybrid Group

Diesel Cummulative Hybrid Cumulative

13.1 mpg

10.2 mpg
v

Table of Contents

Executive Summary......................................................................................................... iii

Evaluation Design ........................................................................................................... iii

Evaluation Results........................................................................................................... iii

Overview.............................................................................................................................1

Advanced Vehicle Testing Activity ..................................................................................1

Project Design and Data Collection ..................................................................................2

Host Site Profile—UPS, Phoenix, Arizona .......................................................................5

Evaluation Results .............................................................................................................5

Van Use .............................................................................................................................5

Van Duty Cycle .................................................................................................................7

Fuel Economy..................................................................................................................10

Maintenance Cost Analysis.............................................................................................12

Maintenance Costs...........................................................................................................13

Reliability ........................................................................................................................16

Batteries...........................................................................................................................17

Laboratory Fuel Economy and Emissions Testing.......................................................18

Test Plan ..........................................................................................................................18

Vehicle Specifications.....................................................................................................20

Laboratory Test Results...................................................................................................21

Status of UPS Hybrid Fleet .............................................................................................23

Conclusions.......................................................................................................................23

Contacts ............................................................................................................................25

Appendix: Laboratory Description and Test Methods................................................26

General Lab Description..................................................................................................26

Chassis Dynamometer.....................................................................................................26

Fuel Storage and Blending ..............................................................................................27

Fuel Metering and Conditioning .....................................................................................28

Air Handling and Conditioning.......................................................................................28

Emissions Measurement..................................................................................................28
1

Overview

Advanced Vehicle Testing Activity

The role of the Advanced Vehicle Testing Activity (AVTA) is to help bridge the gap between 

research and development (R&D) and commercial availability for advanced vehicle technologies 

that reduce petroleum use and meet air-quality standards. AVTA supports the U.S. Department 

of Energy’s (DOE) Vehicle Technologies Program by examining market factors and customer 

requirements and evaluating the performance and durability of alternative-fuel and advancedtechnology vehicles in fleet applications. The National Renewable Energy Laboratory’s (NREL)

Fleet Test and Evaluation (FT&E) team conducts evaluations primarily with support from 

AVTA, but also with support from other DOE programs focused on non-petroleum-based and 

advanced petroleum-based fuels.

The main objective of FT&E projects is to conduct comprehensive, unbiased evaluations of 

advanced-technology vehicles. Data collected and analyzed include the operations, maintenance, 

performance, cost, and emissions characteristics of advanced-technology vehicles and 

comparable conventional technology in fleets operating at the same site. The FT&E evaluations 

help fleet owners and operators make informed vehicle-purchasing decisions. The evaluations 

also provide valuable data to DOE about the maturity of the technology being assessed.

The FT&E team has been conducting several evaluations of advanced-propulsion heavy-duty 

vehicles (see Table 1). Information on these and other evaluations involving advanced 

technologies or alternative fuels, such as biodiesel and Fischer-Tropsch diesel, is available at 

www.nrel.gov/vehiclesandfuels/fleettest.

Table 1. FT&E Heavy-Duty Vehicle Evaluations

Fleet Location Vehicle Technology Evaluation Status

Long Beach 

Transit

Long Beach, 

CA

New Flyer 40-ft low 

floor transit bus Gasoline-electric series hybrid Completed in June 2008

Metro St. Louis, MO GILLIG 40-ft transit 

bus Biodiesel blend (B20) Completed in July 2008

New York 

City Transit

Manhattan, NY; 

Bronx, NY

Orion VII 40-ft transit 

bus

Series hybrid, BAE Systems 

HybriDrive® propulsion system 

(diesel), order of 200 (Gen II); 

order of 125 (Gen I)

Completed in 

January 2008

New York 

City Transit

Manhattan, NY; 

Bronx, NY

Orion VII 40-ft transit 

bus

Series hybrid, BAE Systems 

HybriDrive® propulsion system 

(diesel), order of 125; DDC S50G 

CNG engines

Completed in 

November 2006

Denver RTD Boulder, CO GILLIG 40-ft transit 

bus Biodiesel blend (B20) Completed in October 2006

King County 

Metro Seattle, WA New Flyer 60-ft articulated transit bus

Parallel hybrid, GM–Allison EP50 

System (diesel)

Completed in 

December 2006

IndyGo Indianapolis, IN Ebus 22-ft bus Series hybrid, Capstone 

MicroTurbine (diesel) Completed in 2005

Knoxville 

Area Transit Knoxville, TN Ebus 22-ft bus Series hybrid, Capstone MicroTurbine (propane) Completed in 2005

Norcal San Francisco, 

CA

Peterbilt/378,

Class 8 truck

Cummins Westport ISXG highpressure, direct- injection, liquefied natural gas (LNG) and diesel

Completed in 2004
2

Project Design and Data Collection

This report discusses a 12-month evaluation of six model year (MY) 2007 Freightliner P70H 

hybrids that were placed in service in Phoenix, Arizona, during the second half of 2007. These

hybrid vehicles are evaluated against six MY 2006 Freightliner P70D diesels that were placed in

service in Estrella, Arizona, during the first months of 2007. The diesel vans were chosen by 

using UPS’s database and comparing the average miles per day of the six hybrids to that of 

diesel vans that had the same size and cargo capability and that were located at the two facilities. 

All fueling and maintenance data are collected by UPS from its databases and were shared with 

NREL for this evaluation.

Figure 1. UPS hybrid van

Table 2 presents additional details on Eaton Corporation’s parallel hybrid system, and Figure 2

provides a schematic of the system.

Table 2. Hybrid Propulsion-Related Systems

Category Hybrid Van Description

Manufacturer/integrator Eaton Corporation

Transmission

Fuller medium-duty automated manual

6-speed

Prototype

Motor

Synchronous brushless, permanent magnet

Continuous power, 26 kW

Peak power, 44 kW

Energy storage

Lithium ion batteries

340 VDC

1.8 kWh total storage
3

Figure 2. Eaton hybrid system schematic

Figure 3 shows the primary hybrid components in the Eaton system.

Figure 3. Eaton hybrid system components

Figure 4 shows the primary hybrid components arranged in the undercarriage of a UPS delivery 

van.
4

Figure 4. Eaton hybrid system components on UPS undercarriage

UPS has custom delivery vans built to the company’s specifications. The P70 vehicles in this 

study are manufactured by Freightliner for UPS. Table 3 provides brief descriptions of the 

vehicle systems.

Table 3. Vehicle System Descriptions

Van Specification Hybrid Electric Vans Diesel Vans

Van manufacturer Freightliner Corp. Freightliner Corp.

Van model P70H step van P70D step van

Van model year 2007 2006

Engine manufacturer and model

Mercedes-Benz

MBE 904 4 cyl.

MY 2006

Mercedes-Benz

MBE 904 4 cyl.

MY 2006

Emissions equipment No DPFa No DPF

Retarder/regenerative braking Regenerative braking None

Air conditioning type None None

GVW 15,200 lb 14,360 lb a DPF = diesel particle filter 

Diesel Engine

Electric Motor

Transmission

Front of Vehicle

High Voltage AC Cables

(bright orange)

Power Electronics 

Carrier
5

Host Site Profile—UPS, Phoenix, Arizona

The host site consisted of the two UPS Arizona facilities—Phoenix and Estrella. Estrella is an 

expansion facility located about five miles west of the main Phoenix facility, and it became 

necessary as the Phoenix facility outgrew its footprint. Figure 5 is a site map showing the 

locations of the two facilities in the greater Phoenix area. The vehicles used for this evaluation 

are six hybrids from the Phoenix facility and six standard diesels from the Estrella facility. It was 

not necessary to modify the Phoenix facility in any way to implement the hybrid vehicles into the 

fleet. Drivers were given training on the operation of the hybrids, but no restrictions or special 

accommodations were made for their use; however, UPS did assign them to urban routes rather 

than rural routes to make the best use of the hybrid drive train. Dispatch and maintenance 

practices are the same at both facilities. The Phoenix facility has on-site fueling, and the vehicles 

are fueled by drivers as needed, using an internal fuel card system. The Estrella facility does not 

have on-site fueling; drivers fuel the vehicles at public stations using a corporate fuel card. In 

both cases the drivers need to log their fueling events on their electronic tablets, and the records 

are uploaded to a central database.

Figure 5. UPS Phoenix site map

Evaluation Results

Van Use

Figure 6 shows the average monthly miles driven per van for each van group with ±95% 

confidence interval lines. An accident involving one hybrid van that affected mileage 

accumulation during August and September was not included in the figure. The width of the 95% 

confidence interval gives some idea about how uncertain we are about the average. Van average 

usage did not change significantly during the first nine months of the evaluation period; the 

hybrids consistently were driven fewer miles throughout this period because of their shorter, 

Estrella

(Diesel)

Depot

Phoenix

(Hybrid)

Depot
6

more urban routes. In October and November, the hybrid group showed a dip in average usage 

and an increase in the 95% confidence interval due to calibration issues for three vans; the result

was that these vehicles were not available for service for extended periods of time. Starting in 

October, the diesel group experienced an increase in miles per van resulting from UPS’s

consolidation of routes.

Figure 6. Hybrid and diesel monthly mileage per van

Table 4 presents the average monthly mileage per van during the evaluation period for the two 

groups of vans. The hybrids had a monthly mileage accumulation rate that is 20% less than that 

of the diesel vans (1,403 miles versus 1,758 miles). The average monthly rate was affected by 

downtime because four hybrid vehicles had a combined 7 months of operation impacted by 

extended downtime, as described above. With those 7 months of operation removed, the hybrids 

averaged 93 miles per month more, which was 15% less than that of the diesel group. This lower 

rate could also indicate a more urban duty cycle with lower speeds and more stops per mile. Half 

of this difference is explained by the 7.5% fewer average miles per day driven by the hybrids, as 

discussed in the Van Duty Cycle section of this report. 

UPS Monthly Mileage Comparison

500

1000

1500

2000

2500

Jan-08

Feb-08

Mar-08Apr-08

May-08

Jun-08

Jul-08

Aug-08

Sep-08

Oct-08

Nov-08

Dec-08

Month

Miles per Van

Diesel Avg Mileage Diesel Avg Mileage + 95% CI Diesel Avg Mileage - 95% CI

Hybrid Avg Mileage Hybrid Avg Mileage + 95% CI Hybrid Avg Mileage - 95% CI
7

Table 4. Average Van Miles Driven per Month by Study Group

Van Duty Cycle

GPS data loggers were installed in two vans from each study group to obtain detailed 

information on the routes they were assigned to. Data were collected for one week of operation, 

providing 10 days of “typical” operation for each vehicle group. The data are not representative 

of the entire UPS fleet but only of the P70 vehicles operating out of these two depots. Figure 7

shows a GPS visualization of the routes of the four logged vans. The red and orange traces each 

show one day of the diesel van’s operations out of the Estrella depot. The blue and purple traces 

each show one day of the hybrid van’s operations out of the Phoenix depot. The exact routes 

vary daily, but the depictions shown are typical of a day of operation for that van, as captured by 

the GPS loggers. 

Van Number Start 

Mileage

End 

Mileage

Evaluated 

Miles

Miles per 

Delivery 

Day

Miles per 

Month

663982 59,305 77,899 18594 73.5 1,550

665020 42,559 65,834 23275 93.1 1,940

665044 30,682 51,526 20844 82.7 1,737

665086 32,085 55,248 23163 91.9 1,930

665087 43,875 65,412 21537 86.5 1,795

665150 32,335 51,470 19135 75.9 1,595

Diesel Average 40,140 61,232 21,091 84 1,758

Diesel Stdev 10,976 10,409 1,969 8 164

666131 11,813 24,210 12397 53.7 1,033

666132 15,711 34,997 19286 82.1 1,607

666133 15,598 34,834 19236 76.0 1,603

666139 15,899 32,902 17003 76.2 1,417

666142 14,212 30,224 16012 69.6 1,334

666145 13,732 30,823 17091 68.6 1,424

HybridAverage 14,494 31,332 16,838 71 1,403

Hybrid Stdev 1,583 4,009 2,539 10 212

Difference 25,646 29,900 4,254 13 354

% Difference 64% 49% 20% 15% 20%
8

Figure 7. Hybrid and diesel route visualization

Figure 8 shows the average time (as a percentage) that vans with GPS loggers spent at different 

vehicle speeds. The hybrids spent more time idling and operating at slower speeds than the 

diesels did, and the diesels spent slightly more time operating at higher speeds. 

• The hybrid vans spent 13% of their time at zero speed, about twice the idle time spent by 

the diesels (6.1%).

• The hybrid vans spent 20% of their time in the 0 to 10 mph range, 31% more than the 

diesels did (15%). 

• The hybrid vans spent 18% of their time in the 20-35 mph range, 32% less time than the 

diesels spent there (26%). 

• The hybrids spent 7.6% of their time in the 50-65 mph range, twice as much as the 

diesels did (3.7%). 

• The diesels spent significantly more time above 65 mph (5% vs. 1% for the hybrids). 

This was because the hybrids are speed-limited while the diesel vans are not. 

The greater time spent by the hybrids at slower speeds indicates a more urban duty cycle; had the 

diesel group driven the same exact duty cycle, they likely would have had lower fuel economy as 

a result. Both groups spent about 70% of their non-idle driving time at speeds less than 35 mph, 

indicating that both groups were on city/residential delivery routes. The higher average highway 

speed could also negatively impact the fuel economy of the diesel group as a result of higher 
9

aerodynamic drag. Both groups spent about 8.5% of their driving time at speeds above 50 mph, 

indicating they had similar distances to travel from depot to delivery zone. 

Figure 8. Hybrid and diesel duty cycle breakdown

Table 5 presents other duty-cycle statistics gathered from the GPS data logging. 

• The hybrids’ average driving speed of 22.3 mph was 7% lower than the diesels’ 24.1 

mph. 

• The hybrids averaged 94 stops per day, 90% more than the diesels’ 49 stops.

• The hybrids averaged 1.4 stops per mile, twice as many stops per mile as the diesels’ 0.7.

• The hybrids had 16.9 acceleration events per mile, 22% more than the diesels’ 13.8. 

• The hybrids had 15.8 deceleration events per mile, 19% more than the diesels’ 13.3. 

These statistics indicate that the hybrids were operating in a more dense urban delivery zone than 

the diesels were. The lower speeds and more stops per mile are in line both with the hybrids’ 

greater percent of time spent at speeds lower than 10 mph and the fewer miles driven per month. 

The 7.5% fewer average miles per day explains part of the 15% fewer miles per month 

mentioned in the Van Use section.

UPS Phoenix

Diesel vs Hybrid delivery duty cycle

0

4

8

12

16

20

Zero Speed

0 - 5

 5 - 10 

 10 - 15 

15 - 20 20 - 25 25 - 30 30 - 35 35 - 40 40 - 4545 - 5050 - 55 55 - 60 60 - 65 65 - 70 

70+ 

Vehicle Speed (MPH)

% of Time

Diesel Average

Hybrid Average
10

Table 5. Drive Cycle Statistics from Vans with GPS Loggers from Each Study Group

Cycle Statistics

Diesel 

Average

Hybrid 

Average

Difference 

(Diesel -

Hybrid) % Difference

Distance traveled (miles) 73.7 68.2 5.5 -7.5%

Average speed over cycle (mph) 22.6 19.4 3.2 -14.3%

Average driving speed (mph) 24.1 22.3 1.8 -7.3%

Maximum speed (mph) 74.0 69.2 4.8 -6.5%

Time at idle (s) 732 1725 -993 136%

Maximum acceleration (ft/s2) 12.8 10.0 2.8 -21.8%

Maximum deceleration (ft/s2) -10.0 -10.9 0.9 9.1%

Acceleration (% of total cycle) 44.1 40.0 4.0 -9.2%

Deceleration (% of total cycle) 40.8 35.7 5.1 -12.4%

Average acceleration (ft/s2) 1.9 2.0 -0.1 3.8%

Average deceleration (ft/s2) -2.0 -2.2 0.2 7.5%

Number of acceleration events 1018.3 1150.2 -131.9 13.0%

Number of acceleration events per 

mile 13.8 16.9 -3.1 22.3%

Number of deceleration events 983.1 1077.9 -94.8 9.6%

Number of deceleration events per 

mile 13.3 15.8 -2.5 18.6%

Number of stops 49.2 93.9 -44.7 90.9%

Average duration of stop (s) 14.5 18.4 -3.9 27.3%

Number of stops per mile 0.7 1.4 -0.7 105.9%

Fuel Economy

UPS fuels its hybrids and diesels with standard ultra-low-sulfur diesel (ULSD), which has a 

sulfur content of less than 30 parts per million (ppm). From June through September, three diesel 

vans experienced spikes in their monthly fuel economy: 

• One van had 1 month of high fuel economy results

• One van had 2 months of high fuel economy results

• One van had 3 months of very high fuel economy results.

UPS confirmed that drivers failed to log fueling events during this period of time. In one case, an

impossible number of miles were accumulated without a recorded fueling event. The six suspect 

diesel-group vehicle months of fuel economy data have been removed from the total of 72 

diesel-group vehicle months of results presented in this report. As such, miles used are different 

for the calculation of diesel-group fuel economy than those reported in other sections of the 

report.

Table 6 shows the fuel consumption and economy data for each van in each study group. The

hybrid vans consumed 7,714 gallons of fuel over 101,025 miles for the 12-month period, 

resulting in an average fuel economy for the hybrid vans of 13.1 mpg, which was 28.9% greater 

than that of the diesel van group’s 10.2 mpg (P value = 0.0002).
11

Table 6. Hybrid and Diesel Van Fuel Use and Economy

Hybrid Vehicles

Van Miles

Gallons 

Consumed

Miles per 

Gallon

666131 12,397 989 12.5

666132 19,286 1,395 13.8

666133 19,236 1,455 13.2

666139 17,003 1,357 12.5

666142 16,012 1,281 12.5

666145 17,091 1,237 13.8

Hybrid Total 101,025 7,714 13.1

Diesel Vehicles

Van

Fuel Economy 

Miles

Fuel Economy 

Gallons 

Miles per 

Gallon

663982 15,590 1,463 10.7

665020 23,275 2,203 10.6

665044 19,052 1,819 10.5

665086 20,204 2,322 8.7

665087 21,537 2,181 9.9

665150 19,135 1,706 11.2

Diesel Total 118,793 11,694 10.2

Figure 9 shows the monthly miles per gallon for each van group and cumulative miles per gallon

for each van group. In this figure, the group is considered as a whole, and monthly miles per 

gallon are calculated by considering the sum of the miles and sum of the gallons for the group 

each month. This figure weights all vehicle miles equally and relates directly to the fleet’s actual 

fuel consumption.

Figure 9. Average monthly and cumulative fuel economy

UPS Fuel Economy Comparison

Monthly Average and Cumulative

8

10

12

14

16

Jan

08

Feb

08

Mar

08

Apr

08

May

08

Jun

08

Jul 08 Aug

08

Sep

08

Oct

08

Nov

08

Dec

08

Miles per Gallon 

Diesel group Hybrid Group

Diesel Cumulative Hybrid Cumulative

13.1 mpg

10.2 mpg
12

Figure 10 shows the average monthly miles per gallon for each group of vans with ±95% 

confidence interval lines. This figure considers each group as six individual vehicles and 

averages their monthly miles per gallon results. This figure weights each vehicle equally and 

better takes into account the effect of different duty cycles and miles per day on fuel economy. 

With a small sample size, one outlier can offset the average significantly. The width of the 95% 

confidence interval gives some idea about how uncertain we are about the average. By 

considering each vehicle as an individual and calculating a 95% confidence interval, it is 

possible to understand the consistency of the population’s fuel economy and gain a better 

understanding of how a larger population of vehicles would behave. The average miles per 

gallon results can be different from those obtained when considering the group as a whole, as in 

Figure 9, and in this study, both groups have 1%-2% higher monthly miles per gallon results 

with this calculation, with few exceptions.

Figure 10. Average monthly fuel economy

Maintenance Cost Analysis

This evaluation focuses on van operations spanning 12 of the first 18 months of operation for the 

hybrid vans. This snapshot does not yield enough capital and operating cost data to provide a 

complete understanding of the full life-cycle cost of the hybrid vans, however. Understanding

costs requires an examination of the purchase cost of the vans plus warranty and operation costs. 

Longer term maintenance activities, such as engine rebuilds or replacements and battery

replacements, also must be considered. Finally, it is critical that areas in which cost savings can 

be achieved (e.g., in brake repair) be examined. The intent of this evaluation, however, is to 

capture accurate actual capital and known operations costs associated with the hybrid and diesel 

vehicles for the selected period. This analysis is not predictive of maintenance costs assumed by 

UPS beyond the warranty period. The exact components and warranty periods—as negotiated by 

UPS, Eaton, and Freightliner—are contractual and confidential.

UPS MPG Comparison

5

8

11

14

17

20

Jan-08

Feb-08Mar-08Apr-08

May-08

Jun-08

Jul-08

Aug-08

Sep-08

Oct-08

Nov-08Dec-08

Month

Miles per Gallon

Diesel Avg MPG Diesel Avg MPG + 95% CI Diesel Avg MPG - 95% CI

Hybrid Avg MPG Hybrid Avg MPG + 95% CI Hybrid Avg MPG - 95% CI
13

The hybrid and diesel vans all are new enough that much of the maintenance is completed under 

warranty. All maintenance for the Eaton hybrid drive was done by Eaton mechanics. These 

maintenance costs are not included in the maintenance-cost analysis in this section. Not

accounting for warranty repairs in the evaluation of total maintenance cost does offer an 

incomplete picture of total maintenance cost. Even without warranty costs, however, this 

analysis reflects the actual cost to UPS during the period selected.

Maintenance costs were collected in the same manner for each study group. All work orders and 

parts information available were collected for the study vans, and the maintenance practices are 

the same for both diesel and hybrid study groups. The maintenance analysis discussions include 

only the maintenance data that were gathered during the evaluation period on the study group 

vans.

Maintenance Costs

This cost category includes the costs for parts and for labor, at $50 per hour; it does not include 

warranty costs. All costs related to an accident on a hybrid vehicle have been removed from this 

section as they do not represent the vehicle and powertrain comparison of interest. Cost per mile 

is calculated as follows.

Cost per mile = ((labor hours * 50) + parts cost)/mileage.

The labor rate has been set artificially at a constant rate of $50 per hour so other analysts can 

change this rate to one more similar to their own situations. This rate does not directly reflect 

UPS’s current hourly mechanic rate.

Table 7 shows total and propulsion-related maintenance costs for the two study groups. The 

propulsion-related vehicle systems include the engine; transmission; electric propulsion; exhaust;

fuel; and nonlighting electrical, which includes general electrical, charging, cranking, and 

ignition. The propulsion-related maintenance cost per mile of $0.034 for the hybrid vans was 5% 

less than the $0.036 for the diesel vans. The total maintenance cost per mile of $0.140 for the 

hybrid vans was 8% less than the $0.152 for the diesel vans.

Table 7. Hybrid and Diesel Van Total and Propulsion Maintenance Costs

Study Group Miles Parts Cost

Labor 

Hours

Maintenance 

Cost

Cost per 

Mile ($/mile)

Hybrid total 101,025 $3,985 203.3 $14,148 $0.140

Hybrid propulsion-related 101,025 $38 69.0 $3,485 $0.034

Diesel total 126,548 $7,122 242.8 $19,260 $0.152

Diesel propulsion-related 126,548 $1,545 61.0 $4,594 $0.036

Included in the “total” maintenance cost data are tire replacements, which are a large part of the 

vehicle operating costs and are responsible for spikes in monthly total maintenance costs. 

Cumulative tire expenses are on the same level as cumulative propulsion-related costs for either 

drive train ($0.032/mile to $0.037/mile). Figure 11 shows total monthly and cumulative 

maintenance costs for the two study groups. Tire costs are responsible for most of the spike in 

March ($0.08/mile) for the hybrid group. A group of tire changes during the month of September 

($0.16/mile) is responsible for the spike during that month. While both study groups have similar 

tire replacement costs over the course of the year ($3,688 for hybrids vs. $4,041 for diesels), the 
14

hybrids seem to experience them in large groups that create spikes, while for the diesel group, 

the replacements are spread evenly over the course of the year. This is likely because the hybrids 

were all put in service during the same month in 2007, while the diesels were put in service over 

about 9 months in that same year. This resulted in a much higher standard deviation in evaluation 

start mileages and, as such, a wider range of tire wear-out events. The hybrids had a lower 

average evaluation start mileage; the range of start mileages was one-seventh that of the diesel 

group, as discussed in the Van Use section.

Table 8 shows a breakdown by individual van of the total cost per mile. Total maintenance cost 

per mile between the diesel and hybrid groups had no statistical significance (P value = 0.82). 

Propulsion maintenance cost per mile showed no statistically significant difference between the 

diesel and hybrid groups (P value = 0.95). Fuel cost per mile dominated the total cost per mile 

for both groups, and the fuel cost per mile was 22% less for the hybrid group (P value = 0.0008). 

As such, total cost per mile was 18% less for the hybrid group (P value = 0.0134). The 2008 

average price for diesel was $3.80/gallon, and this figure was used to calculate fuel cost per mile.

Table 8. Hybrid and Diesel Van Total Cost per Mile

Car PWRTRN

Mileage 

Total

Non-Prop Mnt 

($/mile)

 Prop Maint 

($/mile) 

 Fuel Cost 

($/mile) 

 Total Cost 

($/mile) 

663982 Diesel 18,594 $0.142 $ 0.077 $ 0.357 $ 0.576

665020 Diesel 23,275 $0.077 $ 0.032 $ 0.360 $ 0.468

665044 Diesel 20,844 $0.119 $ 0.038 $ 0.363 $ 0.519

665086 Diesel 23,163 $0.141 $ 0.023 $ 0.437 $ 0.601

665087 Diesel 21,537 $0.140 $ 0.017 $ 0.385 $ 0.542

665150 Diesel 19,135 $0.077 $ 0.038 $ 0.339 $ 0.454

Total Diesel 126,548 $0.116 $ 0.036 $ 0.374 $ 0.526

666131 Hybrid Diesel 12,397 $0.112 $ 0.061 $ 0.303 $ 0.476

666132 Hybrid Diesel 19,286 $0.064 $ 0.020 $ 0.275 $ 0.358

666133 Hybrid Diesel 19,236 $0.087 $ 0.020 $ 0.287 $ 0.394

666139 Hybrid Diesel 17,003 $0.089 $ 0.024 $ 0.303 $ 0.416

666142 Hybrid Diesel 16,012 $0.145 $ 0.067 $ 0.304 $ 0.515

666145 Hybrid Diesel 17,091 $0.149 $ 0.029 $ 0.275 $ 0.453

Total Hybrid Diesel 101,025 $0.106 $ 0.034 $ 0.290 $ 0.430

Total Cost per Mile Comparison
15

Figure 11. Total maintenance cost per mile

Figure 12 shows monthly and cumulative propulsion-related maintenance costs for the two study 

groups. The hybrid spike during October and November is due to Eaton recalibration activities

and is responsible for raising the hybrid cumulative propulsion-related maintenance cost per mile 

to parity with that of the diesel group. Three of the hybrid units were experiencing faults related 

to the calibration of a prototype parking pawl in use on these vans. While Eaton covered the

costs for materials, UPS technicians spent time troubleshooting and working with Eaton, and 

these hours generated the spike in propulsion maintenance cost per mile.

Figure 12. Propulsion maintenance cost per mile 

Total Maintenance Cost per Mile

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Jan08Feb08Mar08Apr08May08Jun08Jul08Aug08Sep08Oct08Nov08Dec08

$/mile

Diesel Cumulative Average Diesel Hybrid Cumulative Average

Diesel group Diesel Hybrid Group

$0.140

$0.152

Propulsion Maintenance Cost per Mile

$0.00

$0.02

$0.04

$0.06

$0.08

$0.10

$0.12

Jan08Feb08Mar08Apr08May08Jun08Jul08Aug08Sep08Oct08Nov08Dec08

$/mile

Diesel Group Diesel Hybrid Group

Diesel Cumulative Average Diesel Hybrid Cumulative Average
16

Figures 13 and 14 show a breakdown of total and propulsion-related maintenance costs per mile 

for the diesel and hybrid study groups, respectively. Note the similar percentage breakdowns for 

each category, which indicates that the hybrid drivetrain is not driving maintenance costs any 

more than the standard conventional drivetrain. Also note that for both study groups, the 

complete propulsion system costs an amount similar to the tire-related costs for the group. 

Propulsion system and tire-related costs were 19% and 17%, respectively, for the diesel group 

and 20% and 21%, respectively, for the hybrid group.

Figure 13. Propulsion maintenance cost per mile (diesels)

Figure 14. Propulsion maintenance cost per mile (hybrids)

Reliability

UPS records instances in which a vehicle is not available to load in the morning, as scheduled. 

Scheduled maintenance events of any kind do not get recorded in this way. During this 12-month 

evaluation, there were 253 operational days available for deliveries. That is a total of 1,518 days 

for each study group of six vans. Both groups had a comparable number of missed operational 

Diesel Maintenence Cost per Mile

 Brakes

4%

 Tires

17%

 Other

59%

 Engine

4%

 Transmission

6%

 Electrical

7%

 Batt/chrg sys

1%

Other

19%

 Exhaust

0%

 Fuel System

2%

Total Propulsion

Hybrid Maintenence Cost per Mile

 Tires

21%

 Other

59%

 Engine

6%

 Transmission

7%

 Electrical

4%

 Batt/chrg sys

0%

Other

20% Fuel System

2%

 Exhaust

0%

 Brakes

1%

Total Propulsion
17

days during the first 6 months of the evaluation. In August one of the hybrid vehicles was 

involved in an accident, which caused it to miss 29 operational days during August and 

September. A combined 55 operational days were missed during October and November while

Eaton was troubleshooting faults related to a prototype parking pawl on three of the hybrid units. 

The diesel study group missed a total of 10 operational days during the 12-month study period,

while the hybrid group missed 68 operational days for the reasons mentioned above (excluding 

the accident). Table 9 breaks down the monthly and cumulative uptime percent for each group. 

Figure 15 shows the monthly and cumulative uptime for each group as a percentage of the total 

available delivery days. The 29 days missed because of an accident are not included in Table 9 or 

Figure 15 because that event was outside normal van and powertrain operations.

Table 9. Hybrid and Diesel Van Cumulative Missed Operating Days

Figure 15. Cumulative uptime

Batteries

The Eaton system uses lithium ion batteries supplied by Hitachi for energy storage. They have a 

capacity of 1.8 kWh and operate at a nominal voltage of 340 VDC. These batteries were not 

available to NREL during the evaluation period for detailed evaluation. The batteries are 

included in the power electronics carrier (PEC). Eaton’s records indicate one PEC was replaced 

because of water intrusion during an atypical monsoon flood event. UPS records indicate 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Diesel Monthly % uptime 100% 99.2% 97.6% 100% 100% 100% 96.2% 100% 100% 99.3% 100% 100%

Hybrid Monthly % uptime 100% 100% 97.6% 100% 100% 100% 100% 98.4% 100% 65.9% 85.2% 100%

Diesel Cumulative % uptime 100% 99.6% 99.0% 99.2% 99.4% 99.5% 99.0% 99.1% 99.2% 99.2% 99.3% 99.3%

Hybrid Cumulative % uptime 100% 100% 99.2% 99.4% 99.5% 99.6% 99.7% 99.5% 99.6% 96.0% 95.1% 95.5%

Cumulative Uptime

90%

92%

94%

96%

98%

100%

1 2 3 4 5 6 7 8 9 10 11 12

Month

% Uptime

Diesel Cumulative % uptime

Hybrid Cumulative % uptime
18

preventive efforts to seal the PEC air filter on the hybrids, and these costs are captured as part of 

the maintenance cost analysis under the “electrical” heading. No record of a battery failure or a 

cell failure exists. The service life of the battery is estimated by Eaton at 7 years.

Laboratory Fuel Economy and Emissions Testing

This work comprises chassis dynamometer testing of two UPS delivery vehicles. The remainder 

of this document includes the test plan and results from vehicle testing performed at NREL's 

ReFUEL Research Laboratory. The ReFUEL laboratory description, experimental setup, and 

test procedures can be found in the appendix.

Test Plan

Tests were performed on one 2007 hybrid electric Workhorse P100 delivery van and one 

conventional 2007 Workhorse P100 delivery van during May and June 2007 to determine 

emissions and fuel economy benefits of the hybrid electric powertrain being evaluated at UPS. 

The tests were conducted over three driving cycles: the Combined International Local and 

Commuter Cycle (CILCC), the West Virginia University City (WVU City) cycle, and the 

Central Business District (CBD) cycle. Vehicle exhaust emissions and fuel consumption were 

measured for repeated test conditions. The speed/time traces of each cycle are shown in Figures 

16, 17, and 18.

Figure 16. CILCC trace

Combined International Local and Commuter Cycle 

(CILCC)

0

10

20

30

40

50

60

0 500 1000 1500 2000 2500 3000 3500

Time (s)

Speed (mph)
19

Figure 17. WVU City trace

Figure 18. CBD trace

West Virginia University City Cycle

(WVU City)

0

5

10

15

20

25

30

35

40

0 500 1000 1500

Time (s)

Speed (mph)

Central Business District Cycle

(CBD)

0

5

10

15

20

25

0 100 200 300 400 500 600

Time (s)

Speed (mph)
20

The test vehicles were installed on the chassis dynamometer shown in Figure 19. All sensors 

were monitored and recorded continuously by the ReFUEL data acquisition system throughout 

each test cycle run, unless otherwise noted.

Figure 19. UPS P100 van on NREL’s ReFUEL dynamometer

Vehicle Specifications

Table 10 shows test vehicle information. Due to timing and test vehicle availability, the tests 

were conducted on Workhorse P100 chassis with VT275 engine—not the same chassis or engine 

evaluated in this report at the Phoenix location but still the same hybrid system. While the 

chassis and engine are different, the Eaton hybrid system is the same as the one used on the 

P70H chassis. P100 vans are not necessarily assigned to the same type of routes as the P70 vans 

discussed in the rest of the report.

Table 10. Test Vehicle Information

Engine Transmission GVWR

Test 

Weight

AfterTreatment Fuel Chassis

Conventional 

P100

International 

VT275

Allison 

Automatic

23,500 

lb

17,500 

lb

N/A Diesel Workhorse 

P100

Hybrid P100 International 

VT275

Eaton Parallel 

Hybrid 

Autoshift

23,500 

lb

17,500 

lb

N/A Diesel Workhorse 

P100
21

Laboratory Test Results

All fuel economy and emissions results are averaged from three test runs of each cycle. Fuel 

economy results for the vans are shown in Table 11. The hybrid vans showed a 31%-37% 

improvement in fuel economy over the conventional vans on the tested duty cycles.

Table 11. Fuel Economy of Hybrid and Diesel Van on Various Cycles on Chassis Dynamometer 

Emissions results for carbon dioxide (CO2), oxides of nitrogen (NOx), total hydrocarbons (THC), 

carbon monoxide (CO), and particulate matter (PM) are shown in Table 12. Results that are not 

statistically significant at the 95% confidence level appear in the gray areas. The hybrid vans 

showed some improvement in emissions, but the results varied significantly depending on the 

cycle being run. This variation is not unexpected, because the engines operate at different load 

points with and without the hybrid system. The engine in the hybrid vehicle has not been 

calibrated for hybrid operation. More consistent improvement in emissions may be possible with 

hybrid-specific engine calibrations. Heavy-duty engines are certified with an engine certification 

test but are not certified in chassis. 

Table 12. Average Values for Emission Results of Hybrid and Diesel Vans on Specified Cycles

Figure 20 shows emissions and fuel consumption results on the CILCC duty cycle. The hybrid 

unit produced 25% less CO2, 14% fewer THC, 29% less CO, and 55% fewer PM emissions than 

the diesel unit did. The hybrid also showed a 29% increase in NOx, as well as a 31% 

improvement in fuel economy over the cycle.

CILCC WVU City CBD

Conventional P100 

(mpg) 9.1 6.87 6.83

Hybrid P100 (mpg) 11.99 9.38 9.16

Fuel Economy (mpg) % 

increase w/hybrid 31% 37% 34%

P Value 0.0010 0.0014 0.0024

Diesel Hybrid Hybrid

% diff

P 

Value

Diesel Hybrid Hybrid

% diff

P 

Value

Diesel Hybrid Hybrid

% diff

P 

Value

CO2 

(gram/mile

)

1026 773 -25% 0.0005 1333 933 -30% 0.0001 1396 1017 -27% 0.0021

NOx 

(gram/mile

)

7.52 9.69 29% 0.0014 9.22 10.42 13% 0.0137 10.56 10.56 NS 0.98

THC 

(gram/mile

)

1.47 1.27 -14% 0.0413 3.85 3.27 NS 0.48 1.34 1.17 NS 0.61

CO 

(gram/mile

)

7.59 5.38 -29% 0.0025 14.31 12.07 -16% 0.0097 8.31 8.80 NS 0.13

PM 

(gram/mile

)

0.142 0.064 -55% 0.0148 0.120 0.214 NS 0.15 0.116 0.114 NS 0.37

*NS - % difference is not reported because the P Value indicates the difference is not statistically significant at the 95% confidence level.

CILCC WVU City CBD
22

Figure 20. UPS P100 CILCC results

Figure 21 shows emissions and fuel consumption results on the WVU City cycle. The hybrid unit 

produced 30% less CO2, 16% less CO, and 13% more NOx. The hybrid had a 37% improvement 

in fuel economy over this cycle. There was no statistically significant difference in THC or PM 

emissions.

Figure 21. UPS P100 WVU City results

CILCC Results

0

4

8

12

16

Nox THC CO PM Fuel

Economy

CO2

(kg/mile)

Emissions (g/mile) Fuel Economy (Miles/Gallon)

Diesel

Hybrid

WVU City Results

0

4

8

12

16

Nox THC CO PM Fuel

Economy

CO2

(kg/mile)

Emissions (g/mile) Fuel Economy (Miles/Gallon)

Diesel

Hybrid

+29%

-55%

-14%

-29%

+31%

-25%

+13%

NA

-16%

NA

+37%

-30%
23

Figure 22 shows emissions and fuel consumption results on the CBD duty cycle. The hybrid unit 

produced 27% less CO2 than the diesel did and showed a 34% improvement in fuel economy 

over this cycle. There was no statistically significant difference in THC, CO, PM or NOx.

Figure 22. UPS P100 CBD results

Status of UPS Hybrid Fleet

UPS has been satisfied with the performance of the original 50 (prototype) hybrid electric vans 

over the first year of service. UPS has ordered an additional 200 hybrids to be deployed in 2009 

with additional features and updates.

Conclusions

• Monthly (and cumulative) miles per van for the hybrids were 20% lower than they were 

for the diesels as a result of a more urban duty cycle and lower uptime related to 

troubleshooting and recalibrating prototype components.

• Miles per operational day were 15% lower for the hybrids than they were for the diesels. 

This indicates that the hybrids were assigned more urban routes with more stops per mile 

and more time spent at slow speeds. 

• Fuel economy of the hybrid group was 28.9% greater than that of the diesel group. Had 

the diesel group been operating on the same duty cycle as the hybrids, the improvement 

might have been greater.

• There was no statistically significant difference between the diesel and hybrid groups for 

total maintenance cost per mile (P value = 0.82).

• There was no statistically significant difference between the diesel and hybrid groups for 

propulsion maintenance cost per mile (P value = 0.95).

CBD Results

0

4

8

12

16

Nox THC CO PM Fuel

Economy

CO2

(kg/mile)

Emissions (g/mile) Fuel Economy (Miles/Gallon)

Diesel

Hybrid

NA

NA

-27%

NA +34%

NA
24

• Total operating costs per mile for the hybrids were 15% less than those for the diesels 

(assuming $3.80/gal).

• Emissions testing generally showed a decrease in CO2, THC, CO, and PM but an increase 

in NOx.

• Laboratory fuel economy testing showed a 31% to 37% improvement for the hybrids 

over the diesels.
25

Contacts

U.S. Department of Energy

Energy Efficiency and Renewable Energy

Vehicle Technologies Program

Lee Slezak

Manager, Advanced Vehicle Testing Activity

Phone: 202-586-2335

E-mail: lee.slezak@ee.doe.gov

National Renewable Energy Laboratory

Mike Lammert

Project Engineer

Phone: 303-275-4067

E-mail: michael.lammert@nrel.gov

Kevin Walkowicz

Advanced Vehicle Testing Activity Lead

Phone: 303-275-4492

E-mail: kevin.walkowicz@nrel.gov

United Parcel Service 

Robert K. Hall

Director, Maintenance & Engineering, International Operations

Phone: 404-828-6556

E-mail: rhall@ups.com

Bill Brentar

Automotive Area Manager, Great Basin & Desert Mountain, Pacific Region

Phone: 602-233-4153

E-mail: bbrentar@ups.com

Eaton Corporation

Alex Stuckey

Special Projects Engineering

Phone: 269-342-3105

E-mail: AlexBStucky@Eaton.com
26

Appendix: Laboratory Description and Test Methods

General Lab Description 

The vehicles were tested at the ReFUEL Laboratory, which is operated by NREL and located in 

Denver, Colorado. The lab includes a heavy-duty vehicle (chassis) test cell and an engine 

dynamometer test cell with emissions measurement capability. Regulated emissions 

measurements are performed using procedures consistent with SAE J2711. Instrumentation and 

sensors at the laboratory are maintained with National Institute of Standards and Technology

(NIST)-traceable calibration. Test procedures, calibrations, and measurement accuracies are 

maintained to meet the requirements outlined in the current Code of Federal Regulations (CFR)

title 40, section 86, subpart N. Data acquisition and combustion analysis equipment are used to 

measure vehicle performance and emissions. Other capabilities of the laboratory include systems 

for sampling and analyzing unregulated emissions, on-site fuel storage and fuel blending 

equipment, high-speed data acquisition hardware and software to support in-cylinder 

measurements, and fuel ignition quality testing. Instrumentation and sensors at the laboratory are 

maintained with NIST-traceable calibration.

Chassis Dynamometer

The ReFUEL Chassis Dynamometer is installed in the main high-bay area of the laboratory. The 

roll-up door to the high bay is 14 ft x 14 ft, high enough to accept all highway-ready vehicles 

without modification. The dynamometer is installed in a pit below the ground level, such that the 

only exposed part of the dynamometer is the top of the 40-in.-diameter rolls. Two sets of rolls 

are installed, so that twin-axle tractors can be tested. The distance between the rolls can be varied 

between 42 in. and 56 in. The dynamometer will accommodate vehicles with a wheelbase 

between 89 in. and 293 in. The dynamometer can simulate up to 80,000-lb vehicles at speeds up 

to 60 mph. 

The chassis dynamometer, illustrated in Figure A-1, is composed of three major components: the 

rolls, which are in direct contact with the vehicle tires during testing; the direct current (DC) 

electric motor (380 hp absorbing/360 hp motoring) dynamometer; and the flywheels. 

The rolls are the means by which power is absorbed from the vehicle. The rolls are attached to 

gearboxes that increase the speed of the central shaft by a factor of 5. The flywheels, mounted on 

the back of the dynamometer, provide a mechanical simulation of the vehicle inertia. 

The electric motor is mounted on trunnion bearings and is used to measure the shaft torque from 

the rolls. The energy absorption capability of the dynamometer is used to apply the “road load,”

which is a summation of the aerodynamic drag and friction losses that the vehicle experiences in 

use, as a function of speed. The road load may be determined experimentally if data are available 

or estimated from standard equations. The electric dynamometer is also used to adjust the 

simulated inertia, either higher or lower than the 31,000-lb base dynamometer inertia, as the test 

plan requires. The inertia simulation range of the chassis dynamometer is 8,000–80,000 lb. The 

electric motor may also be used to simulate grades and provide braking assist during 

decelerations. 

The test vehicle is secured with the drive axles over the rolls. A driver’s aid monitor in the cab is 

used to guide the vehicle operator in driving the test trace. A large fan may be used to cool the 

vehicle radiator during testing. The chassis dynamometer is supported by 72 channels of data 
27

acquisition in addition to the emissions measurement, fuel metering, and combustion analysis 

subsystems. 

The dynamometer is capable of simulating vehicle inertia and road load during drive cycle 

testing. When the vehicle is jacked up off the rolls, an automated dynamometer warm-up 

procedure is performed daily, prior to testing, to ensure that parasitic losses in the dynamometer 

and gearboxes have stabilized at the appropriate level to provide repeatable loading. An unloaded 

coast-down procedure is also conducted to confirm that inertia and road load are being simulated 

by the dynamometer control system accurately. Between test runs, a loaded coast-down 

procedure is performed to further ensure the stability of vehicle and dynamometer parasitic 

losses and accurate road load simulation during testing.

Figure A-1. Chassis dynamometer schematic

Fuel Storage and Blending

There are buildings designed specifically for safely storing and handling fuels at the ReFUEL 

facility. The fuel storage shed is 8 ft x 26 ft and holds up to 48 drums (55 gal. each). Features 

include heating/cooling, secondary containment to 25% of capacity, continuous ventilation, 

explosion-proof wiring/lighting, and a dry chemical fire suppression system. 

The fuel blending shed is 8 ft x 14 ft and has a nominal storage capacity of 24 drums. It has all of 

the features of the storage shed plus explosion-proof electrical outlets for powering accessories. 

The fuel blending can be performed on a gravimetric or volumetric basis, with capability for both 

large-scale (L/kg) and small-scale (cc/g) measurements. 

A fuel line inside a sealed conduit delivers the fuel from the supply drum to the fuel 

metering/conditioning system inside the ReFUEL laboratory, eliminating the need for bulk fuel 

storage inside the laboratory. Another fuel line in the same conduit delivers waste fuel back to 

the fuel blending shed for storage (waste fuel is generated only when a fuel changeover requires 

a flush of the system). 
28

Fuel Metering and Conditioning

The fuel metering and conditioning system (Figure A2) supports test work for both the engine and the 

chassis dynamometers. The meter measures volumetric 

flow to an accuracy of ±0.5% of the reading, with a 

manufacturer’s stated reproducibility of 0.2%. An inline sensor measures the density with an accuracy of 

±0.001 g/cc, allowing an accurate mass measurement 

over the test cycle even if the density of the fuel blend 

is not known prior to testing. 

Air Handling and Conditioning

Dilution air and the air supplied to the test engine or vehicle for combustion are derived from a 

common source, a roof-mounted system that conditions the temperature of the air and humidifies 

as needed to meet desired specifications. The system can also pressurize the incoming air to 

simulate sea level combustion. This gives the lab the ability to simulate any altitude between sea 

level and 5280 ft. This air is passed through a HEPA filter, in accordance with 2007 CFR 

specifications, to eliminate background particulate matter as a source of uncertainty in particulate 

measurements. The average inlet air temperature to the vehicle is maintained within a window of 

75°F ± 4°F for all test runs, and average humidity is controlled to 75 grains/lb (absolute) ± 4 

grains/lb. 

Emissions Measurement

The ReFUEL Laboratory’s emissions measurement system supports both the engine and chassis 

dynamometers. It is based on the full-scale exhaust dilution tunnel method with a constant 

volume sampling (CVS) system for mass flow measurement. The system is designed to comply 

with the requirements of 2007 CFR, title 40, part 86, subpart N. Exhaust from the engine or 

vehicle flows through insulated piping to the full-scale 18-in.-diameter stainless steel dilution 

tunnel. A static mixer ensures thorough mixing of exhaust with conditioned, filtered, dilution air 

prior to sampling of the dilute exhaust stream to measure gaseous and particulate emissions.

A system with three venturi nozzles (Figure A-3) is employed 

to maximize the flexibility of the emissions measurement 

system. Featuring 500 cubic feet per minute (cfm), 1000 cfm, 

and 1500 cfm venturi nozzles and gas-tight valves, the system 

flow can be varied from 500 cfm to 3000 cfm flow rates in 

500 cfm increments. 

This allows the dilution level to be tailored to the engine 

size being tested (whether on the engine stand or in a 

vehicle), maximizing the accuracy of the emissions measurement equipment. 

The gaseous emissions bench is a Pierburg model AMA-2000 (Figure A-4, center). It features 

continuous analyzers for THC, NOx, CO, CO2, and O2. The system also features auto-ranging, 

automated calibration, zero check, and span check features as well as integrating functions for 

calculating cycle emissions. It communicates with the ReFUEL data acquisition systems through 

a serial interface. 

 Figure A-2. Pierburg fuel metering system

Figure A-3. Venturi nozzles
29

There are two heated sample trains for gaseous 

emissions measurement: one for HC and another for 

the other gaseous emissions. The NOx and HC 

measurements are performed on a wet basis, while CO, 

CO2, and O2 are measured on a dry basis. Sample 

probes are located in the same plane in the dilution 

tunnel. 

The particulate matter sample control bench, shown in

Figure A-4, is managed by the ReFUEL data acquisition 

system through a serial connection. It maintains a 

desired sample flow rate through the particulate matter 

(PM) filters in proportion to the overall CVS flow, in 

accordance with the CFR. Stainless steel filter holders, 

designed to the 2007 CFR requirements (Figure A-5, 

center), house 47-mm-diameter Teflon membrane 

filters through which the dilute exhaust sample flows. 

The PM sampling system is capable of drawing a 

sample directly from the large full-scale dilution tunnel or utilizing secondary dilution to achieve 

the desired temperature, flow, and concentration characteristics. A cyclone separator, as 

described in the CFR requirements, is employed to mitigate tunnel PM artifacts.

A dedicated clean room/environmental chamber (Figure A-5, left) is inside the ReFUEL facility. 

It is a Class 1000 clean room with precise control over the temperature and humidity (±1°C for 

temperature and dew point). This room is used for all filter handling, conditioning, and weighing.

The microbalance (Figure A-5, right) for weighing PM filters has a readability of 0.1 μg (a CFR 

requirement) and features a barcode reader for filter identification and tracking and a computer 

interface for data acquisition. The microbalance is installed on a specially designed table to 

eliminate variation in the measurement due to vibration. The microbalance manufacturer 

(Sartorius) was consulted on the design of the clean room, to ensure that the room air flow would 

be compatible with the microbalance.

Figure A-5. Class 1000 clean room, filter housing, and microbalance

Figure A-4. Emissions bench
F1147-E(10/2008)

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1. REPORT DATE (DD-MM-YYYY)

December 2009

2. REPORT TYPE

Technical Report

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Twelve-Month Evaluation of UPS Diesel Hybrid Electric Delivery 

Vans

5a. CONTRACT NUMBER

DE-AC36-08-GO28308

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

M. Lammert

5d. PROJECT NUMBER

NREL/TP-540-44134

5e. TASK NUMBER

FC08.3000

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401-3393

8. PERFORMING ORGANIZATION

REPORT NUMBER

NREL/TP-540-44134

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NREL

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National Technical Information Service

U.S. Department of Commerce

5285 Port Royal Road

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14. ABSTRACT (Maximum 200 Words)

This 12-month evaluation is part of a series of evaluations from the U.S. Department of Energy. Through the National 

Renewable Energy Laboratory (NREL), DOE has been tracking and evaluating new propulsion systems in transit 

buses and trucks. This report focuses on a parallel hybrid-electric diesel delivery van propulsion system operated by 

United Parcel Service. The propulsion system is an alternative to the standard diesel system and could enable 

reductions in emissions, primarily particulate matter and oxides of nitrogen, as well as reductions in petroleum use. 

Hybrid propulsion allows for increased fuel economy, which ultimately reduces petroleum use.

15. SUBJECT TERMS

fuel economy; fuel savings; emissions reduction; hybrid electric diesel trucks; medium duty hybrid vehicles; United 

Parcel Service; NREL

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