NEPI Working Paper

What Set of Conditions Would Make the 

Business Case to Convert Heavy Trucks to 

Natural Gas? – a Case Study

Anna Lee Deal

May 1, 2012
Abstract

Benefits to national security, the trade deficit, and the environment of a nation that uses natural gas 

trucks are attractive to society, but it is the trucking industry who would make the capital investment 

and take on the risk of this transition. We ask the question: "What set of conditions would make the 

business case to convert to natural gas trucks?" As a case study, we developed a financial model that 

takes into account the economic and operational factors of converting a heavy truck fleet to 

compressed (CNG) and liquefied (LNG) natural gas. Lynden Inc,. a Pacific Northwest - Alaska based 

trucking company, participated in this process and provided financial modeling and operational insight 

from a trucking industry perspective. This paper provides a detailed overview of what it means to run 

heavy trucks on natural gas and a summary of the economic and operational factors that a trucking 

company must consider. We modeled for three of Lynden's operations: pick-up and delivery (CNG), farm 

pick up (CNG and LNG), and line haul (LNG spark and HDPI engines) to look for the minimum number of 

annual miles per truck needed for an investment in natural gas trucks to be economically attractive. At 

today's fuel prices, conditions are right for many high mileage (>70,000 miles per truck per year) fleets 

to begin testing natural gas trucks where fuel is available. If those tests are successful, then fleets will 

begin to purchase new natural gas trucks as old diesel trucks are retired. Some significant barriers still 

remain to the mainstream adoption of natural gas trucks, but barriers related to fueling infrastructure 

and available engines are beginning to see major breakthroughs. Policy incentives that address 

remaining barriers can help accelerate this transition and make natural gas attractive to lower mileage 

fleets.
iii

Summary

This is an exciting time for heavy-duty natural gas 

trucks. Refueling infrastructure is finally beginning 

to be developed, the price differential between 

natural gas and diesel has reached a tipping point 

where running natural gas is now profitable for 

high mileage fleets, and a higher powered sparkignited engine that will fit a much larger number of 

heavy truck operations will soon be available. 

Policy makers, the trucking community, and 

environmental groups share a common interest in 

running heavy trucks on natural gas for three 

compelling reasons: 

1. Natural gas will remain less expensive and less 

volatile than diesel for the foreseeable future.

2. Natural gas is domestic and abundant. This 

benefits national security and reduces the 

trade deficit. 

3. Natural gas is cleaner burning and emits fewer 

greenhouse gas emissions than diesel. 

This is an attractive possibility for society, but it is 

the trucking industry that would make the capital

investment and take on the risk of this transition. 

This paper asks the question, "What set of 

conditions would make the business case to 

convert heavy trucks to natural gas?" We address 

the risks and rewards of converting a heavy truck 

fleet from diesel to natural gas from the point of 

view of a trucking company. 

As a case study, Lynden Inc., a Pacific NorthwestAlaska based trucking company, has participated in 

this process to provide financial modeling and 

operational insight from a trucking industry

perspective.

This paper provides a detailed overview, as well as 

the pro's and con's, of what it means to run heavy 

trucks on compressed (CNG) and liquefied (LNG) 

natural gas, including the physical properties of 

natural gas as a fuel, fuel tanks, available and 

future engines, refueling options, maintenance, 

and safety requirements. 

There are a number of economic and operational 

factors that a trucking company must consider 

when deciding whether or not to convert a fleet of 

diesel trucks to natural gas. We address the current 

and future price of fuels, additional cost of natural 

gas trucks, reduced fuel economy of engines, 

reduced operating range, additional weight of 

natural gas trucks, LNG venting and tank issues, 

limited engine options, maintenance costs, safety 

upgrades for maintenance shops, and limited 

refueling infrastructure. 

We developed a financial model that takes into 

account fuel price, annual miles per truck, payload, 

fuel economy, operating range, maintenance costs, 

and the additional weight and cost of a natural gas 

trucks for three of Lynden's operations: in-city pickup and delivery (CNG), milk tanker farm pick-up 

(CNG and LNG), and line-haul (LNG spark-ignited 

and HDPI engines). We did not include upgrades to 

maintenance shops because costs and options to 

outsource maintenance vary greatly. 

Based on the model, we estimated the minimum 

number of miles required to generate a 20% 

Return On Investment for each scenario at varying 

diesel fuel prices ($3.50, $3.75, $4.00, and $5.00/ 

gallon) while keeping natural gas prices consistent 

($2.50/ Diesel Gallon Equivalent). 

Since 2010, the price of natural gas ($2 to $5 per

mcf) has dropped to roughly one quarter the price 

of oil ($80 to $120 per barrel) on an energy 

equivalent basis. At these prices, where natural gas

is approximately $1.50/ DGE less expensive than 

diesel at the pump, the line haul and farm pick-up 

LNG operations required a minimum of around 

70,000 miles per truck per year using a sparkignited engine and 140,000 miles for the HDPI 

engine to reach a 20% ROI. Pick-up and delivery 

operations that are not weight sensitive, required 

only 60,000 miles per year. 

Not surprisingly, at lower priced diesel, the 

minimum number of miles required for an 

attractive ROI, increases. Once the price 

differential decreases to $0.75 per DGE, natural gas 

becomes impractical because the number of miles 

required to be profitable exceeds the number of 

miles that can be driven in a year.
iv

At the other end of the spectrum, when diesel is 

$2.50/ DGE more expensive than natural gas, 

natural gas becomes an attractive option for fleets 

traveling 30,000-40,000 miles per year (70,000 

miles for the HDPI engine). At these prices, the 

model was much less sensitive to differences in the 

additional weight and price of natural gas trucks. 

Based on this model, conditions are right for many 

high mileage fleets to begin testing natural gas 

trucks where fuel is available in the next few years, 

even without government subsidies. If those tests 

are successful (i.e. trucks are profitable and 

reliable), then fleets will begin to purchase new 

natural gas trucks as old diesel trucks are retired. 

This is likely to be a gradual process as fleets learn 

to navigate the remaining barriers: 

1. Limited fueling infrastructure means a loss 

of flexibility for "go anywhere" fleets to 

meet customer needs. Operating range is 

limited by the tanks that can fit on a truck 

at an economical price and reasonable 

weight. Until infrastructure is widely 

available, fleets will be limited to centrallyfueled operations and routes where fuel is 

available.

2. Limited engine options. Available engines 

are either too small (8.9L spark) or too 

expensive (15L HDPI) for most operations. 

However, larger spark-ignited engines that 

can meet the needs of many long-haul 

fleets will be available soon.

3. Natural gas trucks are more expensive, 

mainly because of the specialized high 

pressure or super-insulated fuel tanks. This 

is a significant barrier to fleets and owneroperators with limited access to capital.

4. The high cost of upgrading a maintenance 

shop can make an investment in natural 

gas trucks considerably less attractive. Full 

service leases and maintenance packages 

are available, but this is not always 

practical for fleets in rural areas and is 

generally less desirable than performing 

maintenance "in-house."

5. LNG use is limited to operations where 

trucks are refueled every 1-2 days so that 

venting of fuel is not an issue.

6. Additional weight of fuel tanks detracts 

from available payload and revenue. This is 

a concern for fleet managers who are 

constantly looking for ways to reduce 

weight.

7. Fleets are apprehensive about new 

technology. It takes time to learn about 

and carefully test a new kind of truck and 

fuel.

Interest from fleets is likely to increase in the first

quarter of 2013 as two primary barriers, lack of 

refueling infrastructure and limited engine options, 

see major breakthroughs. Policy incentives that 

address remaining barriers can help accelerate this 

transition and make natural gas attractive to lower 

mileage fleets. 
v

Table of Contents

List of Figures ................................................................................................................................................ vi

Acknowledgements ................................................................................................................................... viii

1. Introduction.................................................................................................................................................1

2. What Does it Mean to Run Heavy Trucks on Natural Gas?

 2.1 Natural Gas Fuel Characteristics ...........................................................................................................2

 2.2 Fuel Tanks .............................................................................................................................................3

 2.3 Fuel System ..........................................................................................................................................4

 2.4 Engines ................................................................................................................................................ 5

 2.5 Transmissions and Braking ...................................................................................................................8

 2.6 Maintenance ........................................................................................................................................8

 2.7 Heavy Trucks ........................................................................................................................................9

 2.8 Refueling Process..................................................................................................................................9

 2.9 Refueling Infrastructure .................................................................................................................... 10

 2.10 Safety ................................................................................................................................................ 12

3. Fuel Prices

 3.1 Fuel Prices.......................................................................................................................................... 14

4. Economic and Operational Factors

 4.1 Summary of Economic and Operational Factors ............................................................................... 16

 4.2 Price of Natural Gas ........................................................................................................................... 17

 4.3 Additional Cost of Natural Gas Heavy Trucks ..................................................................................... 17

 4.4 Fuel Economy Penalty ....................................................................................................................... 17

 4.5 Operating Range ............................................................................................................................... 17

 4.6 Weight Penalty.................................................................................................................................. 17

 4.7 LNG Venting, Weathering, and Tank Issues....................................................................................... 18

 4.8 Fuel Quality ....................................................................................................................................... 19

 4.9 Loss of Flexibility ............................................................................................................................... 19

 4.10 Limited Engine Options...................................................................................................................... 19

 4.11 Limited Space for Tanks and Other Equipment........................................................................................ .19
vi

 4.12 Maintenance Costs........................................................................................................................... 19

 4.13 Shop Upgrades................................................................................................................................. 20

 4.14 Leasing ............................................................................................................................................ 20

 4.15 Refueling ......................................................................................................................................... 20

 4.16 Dedicated Fleet Refueling Stations .................................................................................................. 20

 4.17 Side Benefits .................................................................................................................................... 20

5. Lynden Inc. Case Study: What Set of Conditions Make the Business Case to Invest in 

Natural Gas Heavy Trucks?

 5.1 About the Model ...............................................................................................................................21

 5.2 Lynden Scenario Operational Characteristics .................................................................................. 22

 5.3 Model Summaries ........................................................................................................................... 23

 5.4 Model Conclusions .......................................................................................................................... 29

 5.5 Modeling for the Westport HDPI 15L .............................................................................................. 29

 5.6 Importance of Fuel Price ...................................................................................................................30

 5.7 Model Limitations and Alternative Approaches ................................................................................31

 5.8 Feedback from Lynden's People ...................................................................................................... 31

 5.9 Lessons Learned from this Exercise ................................................................................................. 32

6. Who is Currently Using Natural Gas and What Have They Learned?

 6.1 Examples of Heavy-Duty Truck Fleets Using Natural Gas ................................................................. 33

 6.2 Initial Tests ....................................................................................................................................... 34

 6.3 California-Based LNG ........................................................................................................................ 34

 6.4 LNG Outside of California ................................................................................................................. 34

 6.5 CNG in Closed Loop Applications ...................................................................................................... 35

7. Policy Options to Support the Adoption of Natural Gas Heavy Trucks

 7.1 Policy Options to Support the Adoption of Natural Gas Heavy Trucks ............................................ 37

8. Conclusions

 8.1 Conclusions ...................................................................................................................................... 41

References .................................................................................................................................................... 43

Appendix .........................................................................................................................................................47
vii

List of Figures

Box 1. Power and Efficiency of Natural Gas Engines ................................................................................... 8

Box 2. Renewable Natural Gas: Bio-methane and Biogas ......................................................................... 39

Box 3. Other Alternative Fuel Technologies .............................................................................................. 40

Figure 1. Natural Gas and Diesel Physical Properties ..................................................................................... 2

Figure 2. Pro's and Con's of Natural Gas Properties ...................................................................................... 2

Figure 3. Typical CNG and LNG Fuel Systems ................................................................................................. 3

Figure 4. Pro's and Con's of CNG and LNG ..................................................................................................... 4

Figure 5. Pro's and Con's of Spark-Ignited and Compression-Ignited Engines................................................ 6

Figure 6. Specifications for Available Heavy-Duty Natural Gas Engines and Comparable Diesel Engines ...... 7

Figure 7. Natural Gas Engines for Heavy Trucks Currently Under Development ........................................... 7

Figure 8. Maintenance Intervals of Heavy Duty Diesel vs. Natural Gas Engines ............................................ 9

Figure 9. Number of LNG Fueling Stations by State ..................................................................................... 10

Figure 10. Natural Gas Fueling Station Locations .......................................................................................... 10

Figure 11. Proposed 2012-2013 LNG Fueling Station Network ...................................................................... 11

Figure 12. Pro's and Con's of Natural Gas from a Safety Perspective ............................................................ 13

Figure 13. Conversion Factors for Comparing Natural Gas to Diesel ............................................................. 14

Figure 14. Crude Oil and Natural Gas Average Monthly Historical and Commodity Futures Prices .............. 14

Figure 15. CNG and Diesel Price Difference ................................................................................................... 15

Figure 16. CNG and Diesel Retail "at the pump" sale prices .......................................................................... 15

Figure 17. Summary of Economic and Operational Factors. Pro's and Con's ................................................ 16

Figure 18. Estimated Range and Weight Differential for Common Natural Gas Configurations .................... 18

Figure 19. Operational Characteristics for 5 Lynden Scenarios .................................................................... 22

Figure 20. Comparative Model Summary Pick Up and Delivery CNG ........................................................... 23

Figure 21. Comparative Model Summary Farm Pick Up CNG ........................................................................ 24

Figure 22. Comparative Model Summary Farm Pick Up LNG ......................................................................... 25

Figure 23. Comparative Model Summary Line Haul LNG 11.9L Spark ........................................................... 26

Figure 24. Comparative Model Summary Line Haul LNG 15L HDPI ............................................................... 27

Figure 25. Summary if Model Results for 5 Lynden Scenarios ....................................................................... 28

Figure 26. Minimum Annual Miles per Truck for 12% ROI for 5 Lynden Scenarios ........................................ 28
viii

Figure 27. Operational Characteristics that are Profitable, Marginally Profitable,

 and Not Profitable or Practical ....................................................................................................... 29

Figure 28. Impact of Fuel Prices on the Minimum Annual Miles per Truck to Achieve a 20% ROI ..................30

Figure 29. Examples of Heavy Duty Truck Fleets Using Natural Gas .............................................................. 33

Figure 30. Estimated Impact of Suggested Policies on the Minimum Number of Annual Miles per Truck 

 to Achieve 20% ROI .........................................................................................................................38

Figure 31. Proposed Weight Credit for Natural Gas Fuel Tanks (empty weight) ............................................. 39

Figure A-1. Fire Codes Related to Natural Gas Repair Garages and Fuel Systems ......................................... 47
ix

Acknowledgements

This paper would not have been possible without the many people who generously gave their time 

and expertise. Many thanks to: Brian Trice and Robert Carrick, Freightliner; Bob Fry and Andy 

Douglas, Kenworth; James Harger, Mark Watkins, and Shaunt Hartounian, Clean Energy; Mike Tucker, 

Vocational Energy; Jeff Campbell, Cummins-Westport; Stephen Ptucha, Westport; Jim Moore, ESINavistar; John Pettit, Clean Air Power; Scott Lucero, Agility Fuel Systems; Dave Meyers, Lincoln 

Composites; Richard Moskowitz, American Trucking Association; Jeff Shefckik, Paper Transport; 

Charles Musgrove, Dillon Transport; Daniel St-Germain, Robert Transport; Brian Paterski, Schneider; 

Ben McLean, Ruan; Jon Burdick, Josh Drenckpohl, Bob Griggs, Jason Jansen, Jim Jansen, Gail Knapp, 

Dick Korpela, Alex McKallor, Brad McKeown, Charlie Mottern, Dave Seaman, Frank Sharp, Bob Strong, 

and Brad Williamson, Lynden Incorporated; Tony Knowles, Mary Haddican, and Brad Carson, National 

Energy Policy Institute.
1

What Set of Conditions Would Make the Business Case to Convert 

Heavy Trucks to Natural Gas? – a Case Study

1. Introduction

There is a great deal of interest in running heavy 

trucks on natural gas from the trucking industry, 

policy makers, and environmental groups. 

However, there are some significant barriers to its 

mainstream adoption. 

Running heavy trucks on natural gas is appealing 

for three main reasons.

1.) Natural gas will remain less expensive and 

less volatile than diesel for the foreseeable 

future. Natural gas is approximately $1.50 to 

$2.00 per gallon less expensive than diesel

on an energy equivalent basis. Futures 

commodity markets for crude oil and natural 

gas predict that natural gas will remain 

substantially less expensive than diesel in the 

future. Natural gas represents a savings of 20

to 25 cents per mile in fuel costs over diesel. 

Because it is produced domestically, natural 

gas is not impacted by foreign supply and 

prices are less volatile. This price savings and 

stability has caught the attention of the 

trucking industry where fuel is often the 

largest expense. 

2.) Natural gas is domestic and abundant. This 

benefits national security and reduces the 

trade deficit. Recent discoveries of shale gas 

resources have fueled predictions that the 

U.S. will be a net exporter of natural gas by 

2030. If all heavy trucks in the U.S. converted 

to natural gas, we would reduce oil use by

approximately 2 million barrels of oil per day, 

12% of total U.S. oil consumption. At $85 per 

barrel, this translates to reducing our trade 

deficit by over $150 million per day.

The National Energy Policy Institute (NEPI)

has identified that the transition of heavy

trucks to run on natural gas is one of the 

most cost effective potential energy policies 

studied. This transition also reduces oil 

consumption more than any other policy 

measured. 

3.) Natural gas is cleaner burning and emits

fewer greenhouse gas emissions than 

diesel. Natural gas burns cleaner than diesel. 

This allows some natural gas powered trucks 

to meet EPA 2010 standards for criteria air 

pollutants (PM and NOx emissions) without 

heavy after-treatment emissions systems

(e.g. diesel particulate filters and SCR) found 

on EPA 2010 compliant diesel engines. 

From “well to wheels” natural gas vehicles

reduce greenhouse gas emissions by 12-23%

(LNG) and 28% (CNG) compared to ultra-low 

sulfur diesel. Vehicles that use natural gas 

sourced from landfill gas, wastewater 

treatment, and farm waste "biomethane"

generate 85-90% fewer GHG emissions. The 

magnitude of this advantage depends on the 

fuel’s source and processing method. 

Natural gas emits fewer greenhouse gases 

when used as a fuel, however its impact can 

become detrimental if leaked into the 

atmosphere where it can be 25 times more 

potent than CO2 as a greenhouse gas. 

Benefits to both national security and the 

environment make this an attractive possibility for 

society, but it is the trucking industry that would 

make the investment and take on the risk of this 

transition.

This paper addresses the risks and rewards of 

converting a heavy truck fleet from diesel to 

natural gas from the point of view of a trucking 

company. We ask the question: “what set of 

conditions would make the business case to convert 

heavy trucks to natural gas?”

As a case study, Lynden Inc., a Pacific NorthwestAlaska based trucking company, has participated in 

this process to provide financial modeling and

operational insight from a trucking industry 

perspective.
2

2. What Does it Mean to Run Heavy Trucks on Natural Gas?

Converting a heavy truck (class 8, greater than 

33,000 gross vehicle weight) fleet to run on 

natural gas means adjusting to a new fuel. This 

section explains the differences between diesel 

and natural gas fuels and a gives an overview of 

natural gas heavy-duty tractor trailers, engines, 

fuel systems, maintenance, and safety 

requirements.

Natural Gas Fuel Characteristics

Natural gas is composed primarily of methane with 

smaller amounts of propane, ethane, helium, and 

water. It is “lighter than air” at temperatures above 

160° F. Natural gas is either compressed (CNG) or 

super cooled (LNG) so that it can be stored in tanks 

on a truck. 

CNG is stored as a gas under high pressure (3,600 

psi), which reduces its volume to less than 1/100th

of the space it would otherwise occupy. Liquefied

natural gas (LNG) is cryogenically cooled to 

approximately -260 ̊ F where it condenses to a 

liquid that occupies 1/600th the space it would 

occupy at standard temperature and pressure. 

Natural gas contains less energy than diesel on a 

per gallon basis. When comparing LNG and CNG to 

diesel, it is often described in terms of diesel gallon 

equivalent (DGE’s) to account for the lower energy 

content. Figure 1 compares the physical properties 

of diesel to LNG and CNG.

One gallon of diesel contains 128,700 Btu's, the 

amount of energy in 135 cubic feet of natural gas.

At atmospheric pressure natural gas would fill a 

container nearly 1000 times larger than a gallon of 

diesel to get the same amount of energy. 

Compressed to 3,600 psi (CNG), the container

would be 4 times larger, and cooled to -260 

degrees F (LNG) the container would be 1.7 times 

as large. In other words, to carry the same amount 

of energy as diesel, CNG tanks take up 4 times and 

LNG tanks take up 1.7 times as much space.

Natural gas has less energy per gallon than diesel, 

but it is lighter. The energy density (energy per 

pound) of natural gas is higher than diesel, 

however the heavy tanks required to store CNG 

and LNG offset this energy to weight advantage.

Figure 2 summarizes the benefits and 

disadvantages of natural gas fuels.

Property Diesel LNG CNG

Energy Content (Btu/ gal) 128,700 74,700 20,300

Diesel Gallon Equivalent 

“DGE” (gal) 1 gal 1.72 gal 3.7 gal

Diesel Gallon Equivalent 

“DGE” (gal) 1 gal

0.23 cu 

ft

0.49 cu 

ft

Density (lbs./ gal) 6.8 3 1

Energy Density (Btu/lb) 18,250 28,266 28,266

Natural Gas Pro’s Natural Gas Con’s

Less expensive than diesel on an energy equivalent 

basis. National Average (October '11):

 - Diesel: $3.81/ DGE

 - CNG: $2.33/ DGE

 - LNG: $2.17/ DGE

New distribution and refueling infrastructure is required.

Prices are less volatile than oil because natural gas is 

produced domestically and is not impacted by foreign 

supply.

Prices are listed in DGE to account for the difference in 

energy content.

- 1 DGE = .23 cu ft LNG

- 1 DGE = 6.3 gallons CNG

Contains less energy (Btu’s) on a per gallon basis so it requires 

more space on a truck to get the same range.

Compression-ignited natural gas engines are as 

efficient as diesel engines.

Spark ignited natural gas engines are less efficient (10%) than 

a diesel engine.

Cleaner burning fuel allows spark-ignited natural gas 

to use less expensive, lighter weight after-treatment 

devices to meet EPA standards.

Natural gas engines are currently limited to few available 

options (7.6L, 8.9L, and 15L).

Lighter than diesel on a per gallon basis.

- energy density (Btu/ pound) is 50% higher

Tanks are heavier.

Figure 2. Pro's and Con's of Natural Gas Fuel Properties.

Figure 1. Natural Gas & Diesel Physical Properties
3

Fuel Tanks

Fuel storage for natural gas is considerably 

different from that of diesel and accounts for the 

bulk of the additional weight and higher cost of 

natural gas trucks.

CNG is typically stored at 3,600 psi and 70 degrees 

F. These high pressures require very robust 

cylinders. The cylinders typically used in heavy 

trucks are made of a plastic gas-tight container and 

a full composite wrap in order to optimize weight, 

however, these tanks are very expensive. 

An LNG fuel tank is essentially a giant thermos 

constructed as a 1⁄4“ thick stainless steel “tank 

within a tank” with a vacuum and super-insulation 

between the two walls. This vacuum thermos 

design is intended to prevent ambient heat from 

entering the tank and causing evaporation of fuel 

and achieves the highest known thermal efficiency 

(R value exceeds 5000). LNG is typically stored at 

near atmospheric pressure, but the tank design 

must compensate for heat gain and higher 

pressure when not in use. The inner tank is usually 

made of nine percent nickel steel and the outer 

tank is usually made of carbon steel. 

Tanks are generally described by their diesel gallon 

equivalent (DGE) volume. This accounts for the 

lower energy content of natural gas. "Usable fuel" 

is less than actual volume because of the need to 

maintain vapor space in the tank (LNG) and the fact 

that fuel does not flow below pressures of about 

150 psi (CNG). In other words, you cannot use 

every molecule of fuel in a tank. Figure 3 compares 

key variables in CNG and LNG fuel systems. Figure 

4 summarizes the advantages and disadvantages of 

CNG and LNG systems.

1. Effective size is "usable" fuel in diesel gallon equivalents. This accounts for the vapor space (LNG tanks) and the "heat of 

 compression" and residual fuel at low pressure (CNG tanks) which reduces the amount of fuel that is "usable".

 Westport GX LNG storage tanks volume is reduced due to pump displacement for 5% diesel mixture.

2. Range assumes 6 mpg for diesel and 10% fuel economy penalty for "spark" natural gas engines. Compression-ignited 

 natural gas engines have approximately the same fuel economy as diesel and account for 5% diesel mixture.

3. Diesel weight includes diesel tank, fuel and after-treatment system (DPF + SCR + Urea Storage with solution = 546 lbs).

4. Does not include Federal Excise Tax (FET).

5. Westport HD weight assumes that 45 gallon diesel tank, hydraulic pump and diesel weigh 400 lbs.

6. Westport HD fuel system includes HDPI engine, hydraulic pump, and fuel tank.

Fuel Tank Configuration and 

Nominal Size

Effective Size1

"Usable Fuel"

Range2 Fuel System Weight 

(full fuel)

Additional Cost of 

Fuel System Installed4

Diesel 75 gallon 75 DGE 450 miles 1,200 lbs3 --

CNG (5) 15 DGE tanks behind cab 68 DGE 367 miles 2,050 lbs $27,000

CNG (2) 41 DGE side mounted 74 DGE 400 miles 1,650 lbs $35,000

LNG (1) 119 gallon side mounted 60 DGE 324 miles 1,200 lbs $22,000

LNG (1) 150 gallon side mounted 75 DGE 405 miles 1,400 lbs $26,000

LNG (2) 150 gallon side mounted 150 DGE 810 miles 2,800 lbs $45,000

LNG 

Westport 

HD 15L

(1) 119 gallon side mounted 58 DGE 365 miles 1,600 lbs5 $70,0006

Figure 3. Typical CNG and LNG Fuel Systems.
4

Another important factor to consider when 

comparing CNG to LNG is the duty cycle. LNG 

works well in applications where trucks have very 

little down-time so that new cold LNG is 

continually added to the system. If a tank sits idle, 

the gas inside will warm and expand; after about 

five days it will begin to vent into the atmosphere. 

Tank valves are designed to release this pressure, 

so it is not a safety issue. But this equates to lost 

fuel and represents an added cost. In addition, the 

environmental benefits of using natural gas are

negated (methane is 25 times more potent as a 

greenhouse gas than carbon dioxide). CNG tanks 

do not vent over time because the tanks are 

designed to contain gas under high pressure.

LNG tank life should exceed the life of the vehicle, 

however the vacuum will slowly decay over time as 

gasses diffuse into the tank materials causing the 

tank to lose some of its super-insulation 

properties. Once the vacuum within the tank 

decays to a point where the pressure increases by 

more than 40 psi over the course of a day, then the 

tank is no longer considered adequate and needs

to be re-evacuated by a competent maintenance 

facility. This is typically required after the first 4-5 

years and every 2-3 years thereafter. The cost is 

approximately $1,000 per unit and would include 

other minor parts replacement or refurbishment.

Fuel tanks require visual inspections only. No other 

maintenance is required over the life of the tank.

Fuel System:

Natural gas is stored as CNG or LNG, but all engines 

burn natural gas as a vapor. 

In a spark-ignited natural gas engine, which can 

operate on CNG or LNG, the CNG flows from the 

storage tanks into a fuel line, then into a regulator 

to reduce the pressure to engine specifications. 

Delivery of LNG to a spark-ignited engine is

provided by the fuel pressure. There are no pumps 

in the system. When the engine demands fuel the 

pressurized LNG flows out of the tank toward the 

engine. The cold pressurized fuel then passes 

through a heat exchanger, using engine coolant to 

warm and vaporize the liquid into a gas. From this 

point on, the process is the same for CNG and LNG. 

Gas is mixed with air and the exhaust gas 

recirculation (EGR) system before it is introduced 

to the intake manifold system and delivers power 

via a four-stroke internal combustion engine. 

In contrast, Westport's compression ignited HPDI

(High Pressure Direct Injection) engine uses an 

engine driven hydraulic pump, located in the fuel 

tank to move fuel. The pump pressurizes the LNG 

to about 4,500 psi. The pressurized liquid travels 

through a heat exchanger, using engine coolant to 

Compressed Natural Gas (CNG) Pro’s

- Infrastructure is more readily available.

- Trucks can sit idle for weeks without losing 

pressure or "venting."

Compressed Natural Gas (CNG) Con’s

- Space and heavy tanks required to store 

CNG make this impractical for long 

distances.

- Tanks are heavier compared to LNG.

Liquid Natural Gas (LNG) Pro's

- LNG is more dense than CNG, so is more 

practical for long distances.

- Tanks are lighter compared to CNG.

Liquid Natural Gas (LNG) Con's

- Infrastructure is very limited outside of 

California, but is expanding.

- LNG should only be used in applications 

where the truck is working (and being 

refueled) daily to avoid warming fuel and 

"venting."

Figure 4. Pro's and Con's of Compressed Natural Gas (CNG) and Liquefied Natural Gas (LNG).
5

vaporize the pressurized liquid into a pressurized 

gas which is then supplied to the engine.

Engines:

The "spark" in a diesel engine comes from the 

compression of the diesel fuel. Natural gas engines 

can be either spark-ignited or compression-ignited 

with pilot injection of diesel fuel. This can be a 

source of confusion for those learning about 

natural gas trucks. Figure 5 summarizes 

advantages and disadvantages of spark-ignited 

versus compression-ignited engines.

Spark ignited engines use spark plugs similar to a 

gasoline engine and meet EPA 2010 emission 

standards using only a 3-way passive catalyst that 

is lightweight and maintenance free. These 

engines use “stoichiometric” combustion where 

the chemically ideal ratio of fuel and air is burned 

by the engine without any excess of fuel or air left 

over. Like their diesel counterparts, they are able 

to use cooled Exhaust Gas Recirculation (EGR) NOx

control where the EGR system takes a measured 

quantity of exhaust gas, passes it through a cooler 

before mixing it with the incoming air charge to the 

cylinder to lower the in-cylinder temperature and 

reduce oxygen concentration in the combustion 

chamber by diluting the incoming ambient air with 

cool exhaust gases. The Cummins-Westport spark 

ignited engines use EGR, but this is not necessarily 

true for all spark-ignited engines. They are 

approximately 10% less fuel-efficient than a 

comparable new diesel engine due to the lower 

compression ratio. 

Compression ignited engines are virtually the 

same as a diesel engine, except that they are able 

to run on natural gas. Westport's HD system 

injects both diesel (~5%) and the natural gas 

(~95%) into the combustion chamber of the engine 

where the diesel ignites under pressure, which in 

turn ignites the natural gas. These engines operate 

with LNG only, due to the common rail pressure 

(constant 4500 psi) required by the engine. Even 

though these engines operate with 95% cleaner 

burning natural gas, EPA emissions requirements 

call for diesel particulate filters (DPF) and liquid 

urea Selective Catalytic Reduction (SCR) aftertreatment to meet 2010 emission standards. This

requirement and the additional diesel tank, make 

this engine system heavier and more expensive

than the spark-ignited system. However, these 

engines maintain the same fuel efficiency as their 

diesel counterparts. 

“Dual-Fuel” is a term that is sometimes 

inaccurately applied to compression-ignited 

engines that require both diesel and natural gas. 

The term was originally used to describe Clean Air 

Power’s “dual-fuel” engine that can run on 70% 

natural gas and 30% diesel and has the ability to 

run on 100% diesel. It is currently in use in Europe 

and is under development for the U.S.

There are currently only two natural gas engines on 

the market for use in heavy-duty trucks. 1.) the 

spark ignited Cummins-Westport ISL-G 8.9 L and 

2.) the compression-ignited Westport Innovations 

HD 15L engine. Figure 6 shows engine 

specifications for these engines compared to their 

diesel counterparts. ESI- Navistar has a 7.6L sparkignited engine available today for lighter-duty 

applications.

There are also a handful of new engines currently 

under development and being field tested that are 

expected to be “game changers” by filling the niche 

for higher-powered, lighter weight spark-ignited 

engine systems. Among these are spark ignited 

Cummins-Westport 11.9 L and ESI Navistar 13L 

engines. Also under development are an ESI 

Navistar 9.3 L spark-ignited engine and the Clean 

Air Power (CAP) 13L compression-ignited “dualfuel” engine, which will be able to run on 100% 

diesel if natural gas is not available. Cummins has 

also announced that it will be developing a 15L 

spark-ignited engine. (Figure 7)

Retrofit kits are also available that convert existing 

diesel engines to run on natural gas (CNG or LNG). 

Eco-Dual's conversion kit is approved for the 2004-

2009 Cummins ISX 15L engine platform. Converted 

engines use 60-80% natural gas with diesel pilot 

injection and can default to run on 100% diesel at 

any time if natural gas is not available.
6

8

Spark Ignited Engine Pro’s

No DPF or SCR after-treatment necessary to meet 

2010 emission standards 

- Maintenance Free

- Lighter Weight

- No diesel tank required

- Less expensive

- Engine braking capability and manual 

transmission available with the 11.9 L

- Available with CNG or LNG

Spark Ignited Engine Con’s

Lower Compression Ratio means:

- Less fuel efficient (7-10%)

- Limited options available in the near term 

(7.6L, 8.9L, 11.9L, and 15L)

- Engine braking is currently not available with 

the 8.9L.

- Automatic transmission (8.9L) is expensive.

- More frequent maintenance intervals

Compression Ignited Engine Pro’s

Maintains partial attributes of a diesel engine:

- Same compression ratio as diesel

- Same fuel efficiency as diesel

- 475 hp max 

- Engine braking

- Manual transmission options

- Same maintenance intervals

SCR after-treatment provides 5% better fuel 

economy over engines without it.

Greenhouse gas emissions per mile are lower: 

- Well-to-wheels reduction compared to 

ULSD is 25% (HD) vs. 16% (ISL-G LNG).

Compression Ignited Engine Con’s

Heavier system:

- Requires diesel after-treatment systems and 

a diesel fuel tank

- After-treatment system ~ 500 lbs

- Diesel tank and fuel weighs ~400 lbs

Space is required for diesel and diesel exhaust fluid 

(DEF) tanks, so dual 58 DGE (116 DGE) is the 

maximum fuel capacity.

After-treatment maintenance is required.

More expensive than spark-ignited systems ($20,000-

$40,000) and $70,000 more than diesel.

LNG only. Currently not available with CNG.

Figure 5. Pro's and Con's of Existing Spark-Ignited and Compression-Ignited Natural Gas Engines.
7

6.7-7.6 L ISL-G 8.9 L ISX 11.9 L HD 15 L

Diesel Natural Gas Diesel Natural Gas Diesel Natural 

Gas*

Diesel Natural Gas

Manufacturer Navistar 

DT466

ESI Navistar

Phoenix

Cummins CumminsWestportCummins CumminsWestportCummins Westport 

Innovations

Displacement 6.7 L 7.6L 8.9 L 8.9 L 11.9 L 11.9 L 15 L 15 L

Ignition Compression Spark Compression Spark Compression Spark Compression Compression

HPDI

Cylinder Head 4 valve 4 valve 4 valve 2 valve 4 valve 4 valve 4 valve 4 valve

Fuel System Common rail 

system

Throttle 

Body 

Intake 

Manifold

Common rail 

system

Intake 

manifold

Common 

rail system

Intake 

manifold

Common rail 

system

Common rail 

system

2010 

Emissions 

Strategy

Particulate 

Filter and 

advanced 

EGR aftertreatment

Passive 

3-Way

Catalyst

Particulate 

Filter and 

SCR aftertreatment

Passive 

3-Way

Catalyst

Particulate 

Filter and 

SCR aftertreatment

Passive 

3-Way

Catalyst

Particulate 

Filter and 

SCR aftertreatment

Particulate 

Filter and 

SCR aftertreatment

Weight (dry) 1,425 lbs. 1,290 lbs 1,850 lbs 1,625 lbs 2,888 lbs ~2,700 lbs 3,286 lbs 3,243 lbs

Horsepower 210-300 hp 300 hp 330-380 hp 260-320 hp 310-425 hp 320-400

hp

400-600 hp 400-475 hp

Peak Torque 520-869 lbft250-860 lbft1,150-1,300 

lb-ft

660-1,000 

lb-ft

1,150-

1,650 lb-ft

1,450 lb-ft 1,450-2,050 

lb-ft

1,450- 1,750 

lb-ft

Peak Torque 

RPM

1,300 RPM 1,300 RPM 1,400 RPM 1,300 RPM 1,200 RPM 1,200 RPM 1,200 RPM 1,200 RPM

Clutch 

Engagement 

Torque

400 lb-ft 400 lb-ft 550 lb-ft 550 lb-ft 800 lb-ft 800 lb-ft 1000- lb-ft 1000- lb-ft

Engine 

Braking

Exhaust 

brake -yes

No Yes No Yes Yes Yes Yes

Make Cummins-Westport ISX ESI Navistar ESI Navistar Clean Air Power

Displacement 11.9 9.3 13 13

Ignition Spark Spark Spark Compression

Fuel CNG, LNG Biogas CNG, LNG, Biogas CNG, LNG, Biogas CNG, LNG, Biogas, or 

100% diesel

HP 320-425 hp 350 hp TBA 430 hp

Torque 1,450 lb ft 850-1,200 lb ft TBA 1,150 lb ft

EGR Yes No Yes Yes

Test Engine Complete Underway 2011 2012 Complete

Field Test Underway 2011 2012 TBA 2012

Available Q1 2012 TBA TBA TBA

OEM Partner Kenworth, Peterbilt, 

Freightliner, Volvo, Autocar

International International International

Figure 6. Specifications for available heavy-duty natural gas engines and comparable diesel engines.

* The 11.9 L Cummins-Westport will not be available until January 2013, however a limited number are available 

for testing in 2011 and 2012.

Figure 7. Natural Gas Engines for Heavy Trucks Currently Under Development.

* Cummins Inc. has also announced the development of a 15L spark-ignited engine.
8

Transmissions and Braking:

Truck OEM’s offer automatic transmissions with 

torque converter technology for use with sparkignited natural gas engines. This transmission 

multiplies engine torque at start to deliver 

adequate power to the drive wheels and makes the 

most efficient use of fuel. Current (8.9L) sparkignited natural gas engines are designed for use 

with automatic transmissions to enable 

performance over a wide range of applications,

including heavy duty applications, that would not 

otherwise be possible. 

Spark-ignited engines must reduce the 

compression ratio in order for gas to burn and 

provide a richer mixture. Currently, engine braking 

is not available in the 8.9L engine, but this is 

partially compensated by the auxiliary braking 

provided by an automatic transmission. Sparkignited engines are capable of engine braking and 

this will be available with the 11.9 liter engine.

Compression ignited natural gas engines maintain 

the attributes of a diesel engine such as a high 

compression ratio and engine braking. Box 1 has 

additional discussion of power and efficiency of 

natural gas engines.

Maintenance:

Maintenance requirements differ between spark 

ignited natural gas engines and their diesel 

counterparts, but the overall cost is roughly the 

same. Spark-ignited engines require more

frequent valve adjustments, spark plug 

replacement, and specialized oil. This means up to 

approximately 3 cents per mile in additional 

maintenance costs. However, spark-ignited

engines do not require diesel after-treatment 

systems or maintenance (DPF and urea) which is 

estimated to cost 4-5 cents per mile, so overall 

maintenance costs are expected to be similar to or

slightly lower than diesel.

Compression-ignited engines follow the same 

maintenance intervals as their diesel counterparts, 

however the engine and fuel system require 

additional fuel filters and inspections. This adds 

approximately 1.4 cents per mile using outside 

labor and 0.9 cents per mile using internal labor. 

They require the same after-treatment system 

maintenance as a diesel truck, but use less DEF. 

Figure 8 compares the maintenance intervals of 

diesel and natural gas engines.

Some fleets use an accelerated oil change interval 

for the 8.9L engine because it is being used in a 

more severe duty-cycle than it was designed for. 

But this is a product of using a smaller engine, not 

natural gas. The 11.9L engine will better suit these 

types of operations. 

The maintenance costs for a natural gas truck are 

comparable to a new diesel truck, but the upgrades 

required for shops servicing natural gas vehicles 

can be substantial. 

LNG units will start to vent if the tanks are warm 

for more than a few days (CNG tanks do not vent). 

To deal with this potential fire hazard, natural gas 

compliant shops may be required to have sloped 

roofs, methane detection systems, automated

ventilation systems, and explosion proof lighting. 

These improvements can be very expensive. Price 

estimates range between $200,000 and $1 million 

dollars depending on local code requirements and 

size of the shop.

POWER AND EFFICIENCY:

Spark-ignited natural gas engines are not able to 

achieve the high compression ratio (and associated 

efficiency) or horsepower of a diesel engine 

because of the need to prevent pre-ignition and 

engine damage. Most spark-ignited natural gas 

engines on the market today suffer a fuel penalty 

of about 10%, but this is improving. Horsepower is 

limited by the amount of gas that can be supplied 

to the cylinder without creating “engine knock”. 

This is referred to as a “knock limit” (38 hp/ L for 

natural gas). Westport's compression-ignited 

engine can achieve the same compression ratio, 

fuel economy, and horsepower rating as a diesel

engine because it uses direct injection of both 

diesel and natural gas. Current 8.9L natural gas 

spark-ignited engines can achieve a max 320 hp 

and 15L compression ignited engines achieve a max 

475 hp. However, these ratings were chosen based 

on market demand and the technology is capable 

of developing engines with higher power. 

Box 1. Power and Efficiency of Natural Gas Engines.
9

Many maintenance procedures (tires, oil changes, 

etc.) can be done without modifications to the 

shop. Bringing trucks into the shop with low or 

empty LNG tanks minimizes the risk of venting and 

associated fire danger. Performing maintenance 

outdoors may be practical alternative in some 

cases.

Many fleets choose to operate under full service 

lease agreements or outsource the maintenance of 

natural gas trucks in order to remove the 

uncertainty of maintenance costs and shop 

upgrades.

Heavy Trucks:

Heavy-duty natural gas trucks are available in the

U.S. from Daimler-Freightliner (M2 ), Paccar’s 

Kenworth (T800, T440), Peterbilt (384, 386, 388, 

367), Navistar, and Volvo (VNM).

A natural gas (CNG or LNG) heavy truck with the 

ISL-G 8.9L spark ignited engine is $30,000-$45,000 

more expensive than a comparable diesel. LNG 

tanks are slightly less expensive than CNG tanks

assuming equal range requirements. An LNG truck 

with the Westport HD 15L engine is about $70,000 

more expensive than a comparable diesel.. This is 

primarily due to the cost of the fuel system.

The best way to determine an accurate price and 

weight differential for a specific application is to 

obtain a quote. This will also ensure that the fuel 

tanks will work with specific chassis length, 

positioning of the 5th wheel, required turning 

radius, and other necessary equipment.

Conversion kits are also beginning to become 

available. These kits retrofit existing diesel engines

so that they are able to run on compressed or 

liquefied natural gas and include natural gas fuel 

tanks and fuel system. Kits cost between $25,000 

and $40,000 depending on the size and type of the 

natural gas fuel tank.

Refueling Process:

Filling up the “gas tank” may be the most obvious 

difference between a natural gas and diesel truck.

A CNG filling station typically takes natural gas 

from the local pipeline at low pressure and 

compresses it to be stored in above ground storage 

tanks at high pressure. In rural communities, the 

pipeline may not have adequate capacity for a CNG 

filling station. 

CNG refueling equipment can either be “fast fill” or 

“time fill”. A “fast fill” system uses a large 

compressor and a high-pressure storage tank to fill 

the truck tank in about the same amount of time as 

a typical diesel truck, however filling beyond 75% 

requires a slower trickle. These systems require a 

significant amount of electricity to run the 

compressor. A “slow-fill” system is typically used 

where fleets are able to fill over a few hours. In 

both systems, natural gas nozzles lock onto the 

receptacles and form a leak-free seal, similar to the 

Diesel

Cummins

ISL 8.9L

CNG/ LNG 

Cummins

ISL-G 8.9L

Diesel 

Cummins ISX 

15L

LNG 

Westport 

HD 15L

Oil & Filter 15,000 15,000 25,000 25,000

Fuel Filter

15,000 (primary)

30,000 (secondary)

30,000 25,000

High Pressure Diesel 125,000

Low Pressure Diesel 31,250

High Pressure LNG 125,000

Spark Plugs N/A 45,000 N/A N/A

Coolant Filter 15,000 15,000 50,000 50,000

Coolant Change 80,000 60,000 250,000 250,000

Valve Adjustment 150,000 60,000 500,000 500,000

DPF (PM Trap) 200,000 N/A 300,000 300,000

DEF Dosing Filter 200,000 N/A 200,000 200,000

Figure 8. Maintenance Intervals of Heavy Duty Diesel vs. Natural Gas Engines.
10

coupling on an air compressor nozzle. The 

receptacles are designed so that when the nozzle is 

removed the gas is prevented from escaping. Basic 

driver training is required, but personalized 

protective equipment is not necessary.

LNG is typically delivered to the station via tanker 

truck and stored in cryogenic storage tanks. An 

LNG filling station consists of a liquid nitrogen 

(refrigerant) storage tank and a large (~16,000 

gallon) LNG storage tank. LNG is pumped into the 

vehicle like any other liquid fuel, but with more 

sophisticated cryogenic fueling equipment. 

Employee training and protective equipment

(gloves, mask, and apron) are necessary.

According to one LNG user, "refueling the truck is 

different, but simple". The tank looks like a regular 

diesel tank on the side of a truck. The nozzle looks 

like a "race car" nozzle. Drivers put on safety 

equipment (gloves, face shield, and apron) to 

protect their skin from the super-cooled fuel. They 

swipe their cards, hook up the nozzle, and hit a 

button. The computer knows how much fuel the 

truck needs and tells the driver when the tank is 

full. It takes about five minutes to refuel.

Compression-ignited engines require diesel in 

addition to LNG; although the diesel only needs to 

be refilled about 1 out of every 20 times it is 

refueled. 

Fueling Infrastructure:

Natural gas refueling infrastructure has been a 

classic “chicken and egg” scenario, where fueling 

stations will not risk the $1.5M investment without 

a strong customer base and fleets are not willing to 

purchase natural gas vehicles without refueling 

infrastructure in place. 

There are currently 47 LNG stations in the U.S. 

(Figure 9), however only about 1/3rd of those are

open to the public (i.e. you do not need prior 

access or approval) and until recently, there were

essentially no LNG filling stations outside of 

California. CNG is more widely available (936 public 

and private stations nationwide) with the majority 

in the Mid-West (Figure 10), but is still limited 

compared to diesel.

State # of LNG Fueling Stations

California 36

Texas 5

Utah 1

Nevada 1

Alabama 1

Louisiana 1

Arizona 1

Connecticut 1

Figure 9. Number of LNG Fueling Stations by State. 

 Includes private and public stations.

Alternative Fuels and Advanced Vehicles Database

Figure 10. Natural Gas Fueling Station Locations. Includes CNG and LNG stations.

Alternative Fuels and Advanced Vehicles Database
11

Clean Energy (an LNG producer who builds natural 

gas refueling stations) has partnered with PilotFlying J truck stops to build 150 LNG fueling 

stations along major interstate corridors. They 

anticipate having an LNG fueling station every 200 

to 300 miles by July 2013 and double that to 300 or 

400 stations by 2015 to serve all regional routes. 

Chesapeake Energy and Temasek Holdings have 

each invested $150 million in this effort to 

construct a foundational grid of LNG stations for 

heavy-duty trucks. Figure 11 shows the proposed 

locations of LNG stations to be built in 2012 and 

2013.

Infrastructure will first expand from California into 

a Southwest LNG truck re-fueling corridor with 

stations now present in Northern California, 

Arizona, Nevada and Utah. Efforts are also 

underway to create a natural gas vehicle corridor 

in Texas, the “Texas Triangle”, connecting Austin, 

Dallas/ Fort Worth, Houston, and San Antonio. 

Also planned for early opening include stations 

linking Houston with Chicago, Chicago to Atlanta, 

and highways in the mid-west with high truck 

traffic.

Local utilities can also be a source of both CNG and 

LNG. Many utilities produce LNG in order to store 

excess natural gas in the summer months for use in 

the winter and are willing to sell both CNG and LNG 

as transportation fuel. Some utilities are already 

seeking out discussions with the trucking 

community as they consider building fueling 

stations. Because natural gas rates from utilities 

are regulated, they can provide some of the least 

expensive fuel available. 

Until more natural gas refueling infrastructure is 

built, fleets may consider building their own 

refueling stations. A CNG or LNG fueling station can 

cost between $400,000 and $1.5M.

Groups such as Clean Energy or Vocational Energy 

will partner with fleets to design and build, and in 

some cases, operate and maintain a station. 

Fleets can pay for the capital cost of a station or 

Clean Energy will pay for a station and recoup the 

cost over 10-15 years. To be economically feasible, 

fleets should be using 25,000 to 30,000 gallons of 

diesel per month, minimum, assuming the station 

is in a desirable location with public access. Twice 

that amount of fuel would be needed for a 

dedicated fleet location. 

Mobile LNG fueling units are also available for 

fleets operating on temporary jobs. These units 

hold approximately 3,000 DGE. This is about half 

the volume of a delivered load of LNG fuel, so it is

not economical in the long term. Like all LNG 

storage tanks, they will vent if not used or refilled 

every 4-5 days.

Figure 11. Proposed 2012-2013 LNG Fueling Station Network.

Clean Energy
12

Safety:

Natural gas is noncorrosive and nontoxic. Because 

it is lighter than air, it will rise under normal 

atmospheric conditions rather than pooling like a 

liquid fuel. This eliminates the potential for ground 

or water contamination and reduces the 

probability of a fire in the event of a leak, but 

creates additional hazards for the area around the 

ceiling of confined spaces. LNG and CNG are about 

as flammable as diesel, but ignite only under 

concentrations between 5-15%. 

Truck cabs are equipped with methane detectors 

to alert drivers if gas has vented into the cab. 

These warnings need to be taken seriously in order 

to avoid drowsiness and associated safety issues.

Natural gas vehicles are safe and have a proven 

track record. Based on a survey of over 8,000 

natural gas fleet vehicles traveling nearly 180 

million miles, there were a total of seven fire 

incidents in the natural gas fleet, only one of which 

was directly attributable to a failure of the natural 

gas system. 

Natural gas vehicles, fuel systems, maintenance 

facilities, and refueling facilities are heavily 

regulated from a safety standpoint. 

CNG and LNG fuel tanks and fuel systems undergo 

rigorous safety testing and must comply with 

federal standards. They are made of high-strength 

materials designed to withstand impact, puncture 

and, in the case of fire, their pressure relief devices 

(PRDs) provide a controlled venting of the gas 

rather than letting the pressure build up in the 

tank. CNG tanks are designed to “leak before 

breaking” so that if a tank stays in service beyond 

the design life, and experiences excessive fill 

cycles, they will only fail by leakage.

The fuel systems in a natural gas vehicle must 

conform to NFPA standards for safe design, 

installation, inspection, and testing. The CNG 

vehicle fuel containers must meet the Federal 

Motor Vehicle Safety Standard.

LNG has its own safety considerations

- Flammable: While it is not flammable as a 

liquid, if exposed to air, LNG will rapidly expand 

to 600 times its original liquid volume, so small 

leaks can present a significant fire hazard near 

the leak. 

- Large Expansion Ratio: When warmed, LNG 

can build to extremely high pressures (over 

3,000 psi) if trapped in lines causing lines to 

fail. Care must be taken in the design of piping 

systems and during maintenance operations to

assure that liquid cannot become trapped 

between two valves. 

- Cryogenic Temperatures: Liquid LNG is stored 

at very cold temperatures (-260 ̊ F) so presents 

a risk of “cryogenic burning” if skin comes in 

contact with a pressurized liquid stream or by 

touching a fuel line. Eyes and skin should be 

covered when working on LNG systems.

There are also special fire safety requirements for 

repair garages servicing CNG or LNG vehicles. 

Fleets servicing their own vehicles will require 

upgrades to comply with these requirements.

- Natural gas presents an asphyxiation hazard at 

concentrations higher than 21%. Because this 

can present a hazard in indoor environments, 

shops require an air evacuation system.

- LNG does not have an odor, so an approved 

gas detection system in the garage as well as 

lubrication or chassis repair pits is required.

- No open flame heaters or heaters with 

exposed surfaces hotter than 750 ̊ F are 

allowed. 

- The area within 18” of the ceiling is designated 

a Class I, Division 2 hazardous location. This 

means modified lighting and electrical systems 

may be required unless ventilation with at 

least four air changes per hour is provided.

Repair garages servicing CNG vehicles that are not 

performing major fuel system repairs may only 

require explosion proof lighting.

NFPA 30A and state fire, mechanical, and electrical 

codes provide guidance, but allow for site specific 

modifications. The local fire department is 

generally the Authority Having Jurisdiction (AHJ). 

Fleets that have on site natural gas refueling 

equipment must comply with NFPA codes 52, 55, 
13

and 57 for equipment requirements, design, 

construction, site, ventilation, installation, testing, 

emergency equipment, and maintenance and with 

code 52 and 57 for LNG fire protection, personnel 

safety, security, LNG fueling facilities and training. 

See Appendix for a list of National Fire Protection 

Administration Codes related to CNG and LNG 

vehicles, facilities, and fueling equipment. 

Figure 12 summarizes the advantages and 

disadvantages of natural gas fuel from a safety 

perspective.

Natural Gas Safety Pro’s Natural Gas Safety Con’s

Non-toxic and non-corrosive Asphyxiation hazard in enclosed spaces (air evacuation 

and methane detection systems are required)

Does not pool on the ground:

 - Reduced fire hazard at ground level

 - No ground or water contamination

 - Flammable only at concentrations between 

 5% and 15%

Rises “lighter than air”:

- Increased fire hazard indoors at ceiling level 

(modified lighting and electrical systems may 

be required)

 - Rigorous design and testing standards

 - Safe and proven track record for vehicles

Heavily Regulated

- Rapid expansion creates significant fire (i.e. 

explosion) hazard near a leak

- Very high pressures can build if gas becomes 

trapped between two valves causing lines to 

fail (follow proper maintenance procedures)

- LNG: cryogenic burn can occur if skin is exposed 

to liquid gas or fuel line (cover eyes, skin)

Figure 12. Pro's and Con's of Natural Gas from a Safety Perspective.
14

3. Fuel Prices

The price differential of natural gas to diesel is 

the single most important factor to consider in 

modeling the business case for converting a 

fleet to natural gas. Retail prices at the pump 

are generally listed in diesel gallon equivalents 

(DGE’s) to account for the lower energy content 

of natural gas compared to diesel. The 

commodity futures market trades wellhead 

natural gas in MMbtu’s or Mcf units. Figure 13

shows conversion factors for comparing natural 

gas to diesel. 

Until 2005, crude oil prices and U.S. natural gas 

prices moved together, supporting the 

conclusion that the two commodities were 

connected. However, current spot prices and 

futures markets show a persistent disparity 

between oil and gas prices.

The commodity futures market predicts natural 

gas prices to be 65-70% less expensive than oil 

on an energy equivalent basis over the next five 

years. Figure 14 compares historical spot prices 

and commodity futures for West Texas 

Intermediate (WTI) Crude Oil and Henry Hub 

wellhead natural gas. 

The U.S. Energy Information Administration

predicts that crude oil prices will increase to 

about 2.8 times the price of natural gas by 2035 

on an energy equivalent basis. Recognizing the 

extreme volatility of oil prices and the difficulty 

in predicting future prices, they recognize that 

the price of oil could increase to as high as 4.8

times the price of natural gas. 

Fuel Type Units Conversion Factor

Wellhead 

Gas

1000 ft3

(Mcf)

Mcf x 5.8 = 

equivalent energy in a barrel of oil

Wellhead 

Gas

MMbtu $ MMbtu x 1.028 Btu per ft3= $ Mcf

CNG Gallons Gallons CNG x 0.16 = 

diesel gallon equivalent (DGE)

LNG Gallons Gallons LNG x 0.58 = 

diesel gallon equivalent (DGE) 

Figure 14. Crude Oil and Natural Gas Monthly Average Historical and Commodity Futures Prices.

Figure 13. Conversion Factors for Comparing 

Natural Gas to Diesel.

Sources: Historical: U.S. Energy Information Administration

Gas: Henry Hub NYMEX Gulf Coast Spot Price

Oil: Crude Oil (West Texas Intermediate) Spot Price

 Futures: NYMEX Near-Month Contracts www.cmegroup.com

Gas: Henry Hub Natural Gas Trade Date 09/12/11

Oil: Crude Oil (West Texas Intermediate) Trade Date 09/12/11

 Crude Oil (WTI)

 Natural Gas Wellhead
15

Conversely, if demand for natural gas increases 

as it enters the transportation, liquid fuels, and 

overseas markets, then the price of natural gas 

could increase to a point where oil is only 1.1 

times the price of natural gas.

The price differential at the retail end is slightly 

narrower than the commodity prices,

accounting for the cost of refinement, 

distribution, and refueling infrastructure.

Recent retail, at-the-pump sale prices (October

2011) at 320 CNG stations shows CNG an 

average $1.65 less expensive than diesel (42% 

less) and LNG $2.10 less expensive (53% less). 

These average prices are somewhat misleading 

as retail prices vary regionally. At a given 

location, LNG is generally 50 cents more 

expensive than CNG. Figures 15 and 16 show 

the price differential of CNG and diesel (October

2011) for the continental U.S.

Natural Gas (CNG) Information

Reported by Clean Cities ($/DGE)

Diesel Information

Reported by Clean Cities ($/gal)

Average Price/

Standard Deviation

Number of Data

Points

Average Price/

Standard Deviation

Number of Data

Points

New England $2.74 / 1.00 14 $3.91 / 0.19 43

Central Atlantic $2.54 / 0.64 76 $3.80 / 0.23 50

Lower Atlantic $1.80 / 0.54 10 $3.71 / 0.17 50

Midwest $1.94 / 0.53 28 $3.72 / 0.15 112

Gulf Coast $1.96 / 0.62 7 $3.65 / 0.13 23

Rocky Mountain $1.66 / 0.66 70 $3.85 / 0.15 29

West Coast $2.69 / 0.59 120 $4.06 / 0.28 56

NATIONAL AVERAGE $2.33 / 0.77 325 $3.81 / 0.23 363

Figure 16. CNG and Diesel Retail “at the pump” sale prices. September 30th - October 14th, 2011

Includes federal and state motor fuel taxes

A total of 12 LNG price points were collected with an average fuel price of $2.17 per DGE

Clean Cities Alternative Fuel Price Report October 2011

CNG Price 

Difference Relative 

to Diesel

Figure 15. CNG and Diesel price difference Clean Cities Alternative Fuel Price Report Oct 2011

$2.75-$2.00 $1.50-$1.00

$2.00-$1.50 $1.00-$0.25
16

4. Summary of Economic and Operational Factors:

Natural gas is likely to remain significantly less 

expensive in future years, but a number of

economic and operational challenges exist for 

the use of natural gas as a transportation fuel in 

heavy trucks. 

Figure 17 presents a summary of the factors

discussed in previous chapters.

These assumptions are used in our financial 

model to determine savings for converting a 

fleet to run on natural gas. Advantages of 

natural gas over diesel are shown in green, 

disadvantages in blue, and factors that are 

neutral in grey.

Fuel Diesel LNG CNG

Natural gas contains less energy per gallon 128,700 Btu/ gal 74,700 Btu/ gal 20,300 Btu/ gal

Fuel prices are listed in energy equivalent “Diesel 

Gallon Equivalents” DGE’s

1DGE 1.72 gal

0.23 cu ft

3.7 gal

0.49 cu ft

Natural gas is likely to remain substantially less 

expensive than diesel in the foreseeable future

$4 / DGE

$0.68/ mile

$2.50/ DGE 

$0.42-$0.47/ mile

$2.50/ DGE

$0.42-$0.47/ mile

Natural gas is produced domestically and prices are 

not impacted by foreign supply

Extremely volatile 

price 

Less price 

volatility

Less price 

volatility

Natural gas is lighter than diesel 6.8 lbs/ gal 3 lbs/ gal 1 lbs/ gal

Natural gas has more energy per pound 18,250 Btu/ lb 28,266 Btu/ lb 28,266 Btu/ lb

Eliminate environmental risk of fuel spill Pools on ground Evaporates Evaporates

Natural gas has a risk of explosion (enclosed spaces) Non-explosive Explosive Explosive

LNG tanks vent after sitting 4-5 days Does not vent Vents- lost fuel Does not vent

It is more difficult to steal natural gas

Truck Diesel LNG CNG

Natural gas trucks are more expensive (primarily due 

to fuel system)

-- Spark $30-40,000

HD $60-70,000

$30-40,000

Salvage value end of useful life 25% 25% 25%

Depreciable life of tractor 48 months 48 months 48 months

Engine Diesel Spark 8.9L, 11.9L Compression

Spark-Ignited natural gas engines are less fuel 

efficient compared to a new diesel engine

-- 10% less --

Available natural gas engines have limited hp 600 hp max 400 hp max 475 hp max

Maintenance costs are higher for spark engines 

(spark plugs and specialized oil)

-- Up to $0.03/ mi --

Spark-ignited engines do not require DPF or urea 

diesel after-treatment systems

$0.04-$0.05/ mi 200 lbs. lighter 

maintenance free

$0.04-$0.05/ mi

Natural gas engines are quieter than diesel 10 dB quieter 10 dB quieter

Operations Diesel LNG CNG

Operating range is limited to available 

infrastructure, wheelbase, and tank configurations

Max 200 +200 = 

400 DGE; 

Typical 50-100 DGE

Max 75 +75 = 150 

DGE usable;

Typical 50-75 DGE 

Max 75 +40+40 = 

126 DGE usable;

Typical 75-80 DGE 

Cost of additional fueling stop -- $25 per stop $25 per stop

Available payload is usually diminished -- 50 to 600 lbs 

heavier

400 to 1,600 lbs 

heavier

Maintenance shops require safety upgrades 

(lighting, venting, gas detectors)

-- Up to $200,000

per bay

Up to $200,000

per bay

New technology presents a risk Stable technology New technology New technology

Figure 17. Summary of Economic and Operational Factors. Pro's (green), Con's (blue), and Neutral (gray)
17

Price of Natural Gas:

Natural gas price is listed in DGE to account for 

the reduced energy content of natural gas 

compared with diesel. It is currently $1.50-

$2.25 less expensive than diesel and is likely to 

remain less expensive in the foreseeable future. 

Prices currently range between $1.85 and $2.20 

per DGE. We assumed $2.50 per DGE in our 

model as a conservative estimate. 

Additional Cost of Natural Gas Heavy Trucks:

A natural gas heavy truck with the ISL-G 8.9L 

spark-ignited engine is $30,000-$40,000 more 

expensive than a comparable diesel. LNG is 

slightly less expensive than CNG because the 

robust tanks required for CNG are more 

material intensive than the thermos design for 

LNG. A truck with the ISX-G 15L engine is 

$70,000 more expensive than a comparable 

diesel and is available with LNG only.Natural 

gas engines are approximately $10,000 more 

expensive than a comparable diesel engine. The 

higher cost of the truck is primarily due to the 

cost of the fuel system and in the case of 

compression-ignited engines, the diesel aftertreatment system. Prices have come down 

substantially in the last few years due to 

economies of scale. 

Fuel Economy Penalty:

Spark ignited engines are 10% less fuel efficient 

than a comparable new diesel engine. The 

Westport HD 15L compression-ignited engine 

has approximately the same fuel efficiency as a 

comparable new diesel engine.

A truck that averages 6 mpg will save 21 cents 

per mile in fuel costs with a spark-ignited 

engine (10% loss in fuel economy) and 26 cents 

per mile with a compression ignited engine (no 

loss in fuel economy).

Operating Range:

The operating range that can be achieved with a 

given natural gas tank must account for three 

factors: 1.) Account for the reduced energy 

content of natural gas compared to diesel by 

using the rated capacity listed in diesel gallon 

equivalents (DGE). 2) Deduct approximately 

10% from a CNG tank to determine "usable 

fuel." CNG does not flow at low pressures so 

there is always some residual fuel in the tank 

that cannot be used. LNG tanks require vapor 

space which reduces the effective storage 

space, however, this is already accounted for in 

the listed DGE capacity, so does not need to be 

discounted. 3.) Spark ignited natural gas 

engines suffer a 10% fuel economy penalty. 

Compression ignited engines (HD 15L) get the 

same fuel economy as diesel.

Standard tank configurations provide a range of 

250-350 miles with CNG and 300-375 with LNG. 

Some fleets are experimenting with using

additional tanks for increased range, but this 

adds another $20,000-$30,000 to the price of 

the truck. For CNG, the maximum tanks used to 

date include three 25 gallon tanks behind the 

cab (75 DGE) and two side-rail tanks (41 DGE) 

which gives a total usable fuel capacity of 143

DGE and (700-800 mile range), but this 

configuration is very heavy (nearly 3,000 

pounds full of fuel). For LNG, two 150 gallon 

tanks (75 DGE each) would give an 810 mile 

range (assuming 6 mpg with diesel reduced by 

10%, 5.4 mpg for a spark ignited engine).

Westport's 15L HDPI requires additional space 

for the diesel tank, DEF tanks, and hydraulic 

pump inside the LNG tank. Currently, the 

largest LNG tank available with the integral LNG 

pump is a 120 LNG tank, so the 150 gallon tank 

is not an option. Maximum fuel capacity with 

dual 120 gallon tanks is 116 DGE. However, 

there is no fuel economy penalty with this 

engine and 5% diesel provides additional energy 

(730 mile range with dual 120 gallon tanks).

Weight Penalty:

The total "tires to tailpipe" weight of a natural 

gas truck depends upon the type of engine (ISLG 8.9L or HD 15L), the type of fuel (CNG or LNG)

and size of fuel tanks (depending on needed 

fuel capacity). 
18

The table below shows the estimated weight 

differential of the most common natural gas 

configurations based on variables: engine, aftertreatment, fuel system, and fuel. Actual weight

differential will vary by a few hundred pounds, 

depending on which diesel truck is used as a 

base case. A good rule of thumb says that an 

LNG or CNG truck will be 300-600 pounds 

heavier. However, the weight can be very close 

to diesel weights if the natural gas truck is 

configured with lightweight components.

Fuel Type CNG CNG LNG LNG LNG

Engine 8.9L "spark" 8.9L "spark" 8.9L "spark" 11.9L "spark" HD 15L

Tank Configuration 

and Nominal Capacity

(5) 15 DGE

Behind Cab 

75 DGE

(2) 41.2 DGE

Side-Rail

82.4 DGE

(1) 150 gal

Side-Rail

75 DGE

(1) 150 gal

Side-Rail

75 DGE

(1) 120 gal

Side-Rail

58 DGE

Usable Fuel (DGE) 68 DGE 74 DGE 75 DGE 75 DGE 58 DGE

Fuel Economy 

Penalty

10% 10% 10% 10% No

Range (6mpg) 367 mi 400 mi 338 mi 338 mi 365 mi

Engine Weight 1,625 lbs (vs. 

1,800 lbs diesel)

1,625 lbs (vs. 

1,800 lbs diesel)

1,625 lbs (vs. 

1,800 lbs diesel)

2,700 lbs (vs. 

2,888 lbs diesel)

3,243 lbs (vs. 

3,286 lbs 

diesel)

Fuel System Weight 

(Full Fuel)

2,050 lbs (vs. 

510 lbs diesel)

1,650 lbs (vs. 

510 lbs diesel)

1,400 lbs (vs. 

510 lbs diesel)

1,400 lbs (vs. 

510 lbs diesel)

1,802 lbs (vs. 

510 diesel)

After-Treatment 

System Weight

100 lbs 

(vs. 550 diesel)

100 lbs 

(vs. 550 diesel)

100 lbs 

(vs. 550 diesel)

100 lbs 

(vs. 550 diesel)

550 lbs

(vs. 550 diesel)

Weight Differential of 

Variables (engine, 

fuel system, aftertreatment)

-175

+1,540

-450

-175

+1,140

-450

-175

+890

-450

-188

+890

-450 lbs

-43

+1,292

-0

Total Weight 

Differential natural 

gas vs. diesel

915 lbs heavier 515 lbs heavier 265 lbs heavier 252 lbs heavier 1,249 lbs 

heavier

Notes:

1. Range assumes 6mpg for diesel and LNG HD 15L compression ignited engine and 5.4 mpg for 8.9L and 11.9L 

spark-ignited engines

2. Fuel system for HD 15L LNG configuration assumes LNG fuel system weighs 1,400 lbs full fuel, 45 gallon diesel 

tank and accessories weighs 96 lbs and diesel weighs 6.8 lbs per gallon (1,802 lbs total).

3. Weight differential is compared to a 75 gallon diesel tank (81 lbs) and diesel weighs 6.8 lbs per gallon (510 lbs).

4. After-treatment system for spark ignited engines is a simple 3-way catalyst (100 lbs) and for compression (HD 

15L) and diesel engines includes DPF, SCR, and urea storage with solution (550 lbs).

LNG Venting, Weathering, and Tank Issues:

Venting or "off-gassing" occurs when LNG 

warms and expands to the point that the tank 

releases excess pressure to the atmosphere 

through the pressure relief valve. This equates 

to lost fuel and reduced savings. It also 

negates the environmental benefit of using 

natural gas because methane is 25 times more 

potent as a greenhouse gas than carbon 

dioxide. 

If new cold LNG fuel is added to the system on 

a daily basis this is not a problem, so LNG 

should only be used in operations where the 

truck has very little down time. Gas will warm 

Figure 18. Estimated range and weight differential for common natural gas configurations. 

(Compared to diesel truck with 75 gallon fuel tank - weight differential will vary depending on base truck).
19

to the point that it will begin to vent only after 

about 4 to 5 days of not being refilled. The 

tanks are designed to release this pressure, so it 

is not a safety issue.

The super-insulation properties of an LNG tank 

gradually degrade over time, decreasing the 

amount of time that a tank can sit idle without 

venting. When the amount of pressure that 

builds over the course of a day exceeds 40 psi, 

the vacuum in the tank needs to be reevacuated. This generally occurs after about 5 

years and every 1-2 years thereafter. Loss of 

vacuum can also occur if there is damage to the 

tank from a collision or other accident.

If venting occurs on a regular basis, 

"weathering" can become an issue. When LNG 

vents, the lighter methane molecules vent first. 

Over time, the residual fuel will contain a higher 

proportion of heavier butane, propane, ethane, 

and helium, than would otherwise exist and will 

be of lower fuel quality.

There have been some reports of LNG fuel lines 

freezing and causing problems. However, this is 

thought to be related to LNG pump 

replacement where the LNG pump is removed 

and the empty LNG tank becomes exposed to 

the environment, not from everyday use.

Venting and icing is not an issue with CNG.

Fuel Quality:

As with diesel, fuel quality is important. Fuel 

should have a high methane content, or drivers 

may feel loss of power. Impure fuel can cause 

plugged filters.

Loss of flexibility:

Loss of flexibility and loss of a "go anywhere" 

fleet is a concern for a fleet that converts to 

natural gas. Fleets want to be able to respond 

to customer needs wherever those might be. 

Until widespread infrastructure is developed, 

natural gas fleets will be limited to operations 

within range of a limited number of natural gas 

fueling stations.

Limited engine options:

There are currently only two natural gas 

engines available for heavy trucks: the Cummins 

Westport 8.9L spark-ignited engine and the 

Westport 15L compression-ignited engine (LNG 

only, heavier, and more expensive). Medium 

duty delivery trucks are currently limited to the 

ESI Navistar 7.6 L engine. A typical 80,000 GVW 

truck is pushing the limits of the 8.9L engine 

and is limited to flat terrain. However, the 11.9L 

spark-ignited engine will be available 1st 

quarter of 2013 and will fit a much larger 

number of heavy truck applications. As demand 

for natural gas trucks increases, more options 

will become available. Additional engines are 

also currently under development (Figure 7).

Limited Space for Tanks and Other Equipment:

LNG and especially CNG tanks take up more 

space than diesel tanks. This can limit the 

amount of space available on the truck for 

pumps or other equipment that might be 

required. On a 3-axle tractor, side-rail mounted 

CNG/ LNG tanks can fit on as short as a 177" 

wheelbase, but this is very tight and makes tank 

servicing more difficult. A 190" wheelbase is a 

more typical wheelbase for side-rail mounted 

tanks. Some drivers have complained that it is 

difficult to see when backing up with the "backof-cab" CNG tanks.

Maintenance Costs: 

Maintenance costs are $0.025 to $0.03 more 

per mile for the spark-ignited engines (due to 

spark plugs, overhead valve adjustments, and 

specialized oil). However, they require no 

diesel after-treatment system maintenance

($0.04-$0.05 per mile), so overall represent a 

cost savings of approximately $0.01-$0.02 per 

mile. 

Maintenance for a compression-ignited engine 

is the same as for a diesel engine, but with 

approximately $0.01 per mile in additional fuel 

filters and inspections. However, less DEF is 

used compared to a diesel, so this additional 

cost may be negated. 
20

Shop Upgrades:

Upgrades required for shops servicing natural 

gas vehicles can be substantial. Natural gas 

compliant shops may be required to have 

methane detection systems, automated 

ventilation systems, and explosion proof 

lighting. This can cost up to $200,000 per bay

depending on local code requirements. Shops 

servicing only CNG vehicles that are not doing

major fuel system repairs may require only 

explosion proof lighting, however this will vary 

depending on local fire code requirements.

Many fleets choose to operate under full 

service lease agreements or outsource the 

maintenance of natural gas trucks in order to 

remove the uncertainty of maintenance costs 

and shop upgrades. Outdoor, unenclosed shop 

bays may be another practical alternative.

Leasing:

Natural gas trucks are available under a fullservice lease. This reduces the burden of the 

high incremental cost and the uncertainty 

around maintenance and shop upgrades and 

allows for immediate savings for high mileage 

fleets. It also allows fleets to test natural gas in 

their operations now, while they wait for the 

11.9L engine to become available. However, 

the monthly lease charge for a natural gas truck 

can be nearly double that of a comparable 

diesel truck and operating charge is $0.03 per 

mile higher. 

Refueling:

Refueling with LNG is as fast as refueling with 

diesel, but safety equipment (gloves, goggles, 

apron) is required to protect skin from 

cryogenic burns that would result from contact 

with the super-cooled fuel.

CNG filling times depend upon the size of the 

compressor and high pressure storage tank. 

New stations with large compressors and 

storage tanks can pump at 8 gallons per minute, 

but filling time will increase if a number of CNG 

trucks refuel back-to back. At older CNG 

stations or stations with smaller compressors, it 

can take 30 minutes or more to fill as the 

compressor fires up to trickle fill the tanks to 

full capacity.

Dedicated Fleet Refueling Stations:

A fleet that is interested in refueling "on-site" 

should be using approximately 250,000 DGE per 

year for CNG and 500,000 DGE per year for LNG 

in order to make the investment in a refueling 

station economically viable and in the case of 

LNG, to minimize venting issues. A delivery of 

LNG to the refueling station should be made 

about every 3-4 days to minimize venting issues 

and lost fuel. If other fleets are involved, or if 

the station is in a desirable location for publicprivate use, then lower volumes may be viable 

(i.e. the station could be built at no cost to the 

fleet by the natural gas fuel supplier).

Side Benefits:

Ultimately, the decision to invest in natural gas 

is an economic and functional decision, but 

there are a handful of side benefits to its use.

- Engines are quieter (about 10 decibels)

than a diesel.

- There is no need for #1 diesel in the 

winter which is a more expensive and 

less efficient fuel than #2 diesel.

- It is much more difficult to steal natural 

gas, as can sometimes be a problem 

with diesel.

- It adds a new dimension to customer 

relations. Fleets can help customers 

reduce costs and meet their 

sustainability goals. Bio-methane 

sourced from landfill gas, wastewater 

treatment, and farm waste presents an 

opportunity to be "carbon negative" 

and in some cases partner with 

customers to use their waste as fuel.

- If future air quality regulations become 

more stringent, natural gas has more 

potential to improve air quality costeffectively compared to diesel. 
21

5. Lynden Inc. Case Study: What Set of Conditions Make the Business Case for an 

Investment in Natural Gas Heavy Trucks?

The large fuel price differential between natural 

gas and diesel is very attractive, but is it enough 

to overcome the economic and operational 

factors that come with natural gas heavy 

trucks? 

Lynden Inc., a Pacific Northwest-Alaska based 

transportation company partnered with the 

National Energy Policy Institute on this project 

to develop a financial model and gain insight 

into the economic and operational conditions 

that would lead a heavy truck fleet to invest in 

natural gas trucks. 

The Lynden family of companies capabilities 

include: truckload and less-than-truckload 

transportation, scheduled and charter barges, 

rail barges, intermodal bulk chemical hauls, 

scheduled and chartered air freighters, 

domestic and international air forwarding, 

international ocean forwarding, customs 

brokerage, trade show shipping, remote site 

construction, sanitary bulk commodities 

hauling, and multi-modal logistics.

About the Model:

We use a profit-and-loss model to find annual 

cost or savings per mile, per truck, and per fleet. 

The model accounts for the economic and 

operational factors summarized in figure 17. 

1. Fuel price. We modeled for cost of 

diesel at $3, $4, and $5 per gallon while 

leaving the cost of natural gas constant 

at a conservatively estimated $2.50 per 

diesel gallon equivalent (DGE).

2. Weight differential. Weight differential 

comes from OEM quotes and compares

natural gas to a comparable new diesel 

truck using design specifications for 

trucks used in each operation. The 

additional weight of a natural gas truck 

translates to a percentage of reduced 

payload and additional miles needed to 

travel per year to make up for the loss 

in payload (cost per mile estimated at

$3.10 per mile). We used full fuel 

weights and full urea (diesel aftertreatment system) weights.

3. Fuel Economy and Operating Range. 

Operating range is based on "usable" 

fuel and accounts for a 10% fuel 

efficiency penalty for spark-ignited 

engines. For the HDPI engine, there was 

no fuel economy penalty. Each 

additional fuel stop needed to 

compensate for reduced fuel range is 

estimated to cost $25 to account for 

additional time and labor. 

4. Price differential, depreciable life, and 

salvage value of the truck. Truck prices 

came from actual OEM quotes and 

compare natural gas to a comparable 

new diesel truck including Federal 

Excise Tax (FET). We assumed a 

depreciable life of 4 years for the truck 

(conservative estimate) and equal 

salvage values (25%) for diesel and 

natural gas trucks at the end of their 

useful life.

5. Maintenance costs. We assumed 

maintenance costs to be equal between 

natural gas and diesel trucks. This is 

based on a $0.03/ per mile increased 

cost for spark-ignited engines (spark 

plugs and specialized oil) and a $0.01-

$0.04/ mile savings by eliminating 

maintenance costs associated with 

diesel after-treatment systems.

6. Shop upgrades. We did not include the 

cost of maintenance shop upgrades in 

this model. Costs vary greatly 

depending on the size and location of 

the shop and options for outsourcing 

maintenance may be more practical.
22

Lynden Scenario Operational Characteristics (we modeled 3 operations, a total of 5 scenarios):

1. In-City Less-Than-Truckload (LTL) Pick-Up and Delivery: CNG

2. Milk Tanker Farm Pick Up: CNG and LNG

3. Truckload and Less-Than-Truckload Line Haul: LNG 11.9L "Spark" engine and LNG 15L HDPI

Key variables are summarized in figure 19; results are presented in figures 20-26.

LTL Pick-Up & Delivery (CNG):

This is a 15 tractor fleet 

based in the Seattle area. 

The 69,000 GVW tractor with 

semi-van trailer operates

within a 50 mile radius to 

provide pick-up and delivery 

service from a central 

terminal and travels an 

average 14,000 miles per 

year. There are currently 

four CNG fueling stations in 

the Seattle area with enough 

space available for a truck to 

refuel. CNG quote is for an 

8.9L spark-ignited engine.

This operation is not weight 

sensitive because truck is 

rarely loaded to full capacity, 

so the weight penalty was 

removed from the model for 

this scenario.

Farm Pick Up (CNG & LNG):

Tractors with tank trailers

pick up milk from the dairy 

farm and deliver to the

processing plant. The 8 truck

fleet carries loads up to 

105,500 GVW within a 30 

mile radius of the terminal 

on flat terrain. The 8.9L 

engine is beyond its upper 

limit for this application.

Each truck averages 60,000 

miles per year. Refueling 

infrastructure is currently not 

available, but annual fuel use 

and terminal location make 

this a potentially feasible

public/private refueling site.

We compared the diesel to 

CNG and LNG trucks. This is 

an extremely weight 

sensitive operation.

Line Haul (LNG):

Line haul refrigerated trucks 

with team drivers specialize 

in transporting seafood and 

other refrigerated freight 

from the Pacific Northwest 

to Central and Southern 

California, Portland, Boise, 

Salt Lake City, Denver, 

Minneapolis, Chicago, and 

Boston. GVW is 80,000 

pounds and trucks average 

150,000 miles per year. The 

11.9L engine is at its upper 

limit for this application. For 

the model, we assume LNG

refueling infrastructure is 

available for these corridors. 

We compared the diesel and 

LNG 11.9L engine and HDPI 

15L. This operation is also 

weight sensitive.

LTL Pick Up & 

Delivery CNG

Farm Pick Up 

CNG

Farm Pick 

Up LNG

Line Haul LNG

11.9

Line Haul LNG

HDPI

Engine Size 8.9L 8.9L 8.9L 11.9L HDPI

Fleet Size 15 trucks 8 trucks 8 trucks 50 trucks 50 trucks

Annual miles per truck 14,000 miles 60,000 60,000 150,000 150,000

MPG Diesel

MPG Natural Gas

5.91 mpg

5.32 mpg

4.7 mpg

4.23 mpg

4.7 mpg

4.23 mpg

5.89 mpg

5.28 mpg

5.89 mpg

5.89 mpg

Additional Cost of 

Natural Gas Tractor $29,000 $40,000 $43,000 $34,000 $67,000

Additional Weight of 

Natural Gas Tractor n/a 1,556 lbs 555 lbs 68 lbs 500 lbs

Payload Diesel

Payload Natural Gas n/a 75,000 lbs73,444 lbs

75,000 lbs

74,450 lbs

45,000 lbs

44,932 lbs

45,000 lbs

44,500 lbs

Tank Size Diesel 50 gallons 75 gallons 75 gallons 90 gallons 90 gallons

Tanks Size NG Nominal

Tank Size NG DGE

Tank Size NG Usable

(2) 25 DGE

50 DGE

45 DGE

(5) 15 gallon BOC

75 DGE

68 DGE

150 gallon

75 DGE

75 DGE

150 gallon

75 DGE

75 DGE

120 gallon

58 DGE

58 DGE

Range Diesel

Range NG

296 miles

240 miles

353 miles

288 miles

353 miles

296 miles

531 miles

396 miles

531 miles

354 miles

Figure 19. Operational Characteristics for 5 Lynden Scenarios Diesel vs. Natural Gas
23

Model Summaries:

Figure 20. Comparative Model Summary: In-City Pick Up & Delivery 8.9L Spark-Ignited CNG vs. Diesel
24

Figure 21. Comparative Model Summary: Farm Pick Up 11.9L Spark-Ignited CNG vs. 11.9L Diesel 
25

Figure 22. Comparative Model Summary: Farm Pick Up 11.9 L Spark-Ignited LNG vs. 11.9L Diesel
26

Figure 23. Comparative Model Summary: Line Haul 11.9L Spark-Ignited LNG vs. 11.9L Diesel
27

Figure 24. Comparative Model Summary: Line Haul 15L HDPI LNG vs. 15L Diesel
28

In City Pick Up 

and Delivery

CNG

Farm Pick Up 

CNG

Farm Pick Up 

LNG

Line Haul LNG

11.9L Spark

Line Haul LNG 

HDPI

Annual (Cost) and Savings per mile

Diesel $3 per gallon ($0.37) ($0.16) ($0.12) ($0.03) ($0.06)

Diesel $4 per gallon ($0.20) $0.05 $0.10 $0.14 $0.11

Diesel $5 per gallon ($0.03) $0.27 $0.31 $0.31 $0.28

Annual (Cost) and Savings per truck

Diesel $3 per gallon ($5,185) ($9,574) ($6,983) ($3,695) ($9,184)

Diesel $4 per gallon ($2,182) $3,192 $5,783 $21,458 $16,239

Diesel $5 per gallon ($439) $15,958 $18,548 $46,882 $41,663

Annual (Cost) and Savings per fleet

Diesel $3 per gallon ($77,778) ($76,589) ($55,865) ($198,271) ($459,214)

Diesel $4 per gallon ($42,185) $25,537 $46,261 $1,072,907 $811,964

Diesel $5 per gallon ($6,591) $127,663 $148,387 $2,344,085 $2,083,142

Return on Investment (ROI) = annual savings/ additional cost of tractor

Diesel $3 per gallon (18%) (24%) (16%) (12%) (14%)

Diesel $4 per gallon (8%) 8% 13% 63% 24%

Diesel $5 per gallon (2%) 40% 43% 137% 62%

Figure 25. Summary of Model Results for 5 Lynden Scenarios. 

 (Cost) and Savings includes operating costs and annualized capital costs

ROI = annual profit/ additional cost of the natural gas tractor

Figure 26. Minimum Annual Miles per Truck for 20% Return On Investment for 5 Lynden Scenarios. 

(Assume Natural Gas is $2.50/ DGE)
29

 

Model Conclusions:

No model is perfect, however this model is a 

useful tool for predicting which operations 

make business sense for natural gas. Figure 26

shows the minimum number of miles per truck 

needed at various fuel price differentials to 

achieve a 20% Return on Investment (ROI) while 

taking into account the high incremental cost of 

the natural gas truck, loss of fuel economy, loss 

of payload, maintenance costs, and reduced 

operating range.

Return objectives are set by each company 

based on their unique circumstances such as 

cost of capital, amount of leverage, shareholder 

return expectations, and perceived risk of the 

investment. The Return On Net Asset threshold 

for four publicly traded trucking companies over 

the last 5 years ranged from 5.7% to 25.6% 

(average 12.1%.) A 20% threshold is on the high 

end of what a business would use as an

investment criteria for this type of model, but is 

in line with the high perceived risk of investing 

in new technology like natural gas trucks.

Assuming $4.00 per gallon diesel and $2.50 per 

DGE natural gas (today's approximate prices), 

LNG fleets traveling more than 70,000 miles 

achieve a 20% Return on Investment. The 

minimum number of miles for a fleet of CNG 

trucks to achieve a 20% ROI ranges between 

60,000 and 90,000 miles per year, depending on 

the actual cost of the tractors and the 

sensitivity of the operation to weight. 

Modeling for the Westport HDPI 15L:

We also modeled the Westport HDPI 15L for the 

Line Haul scenario. For a truck with a single 120 

gallon (58 DGE) tank, this added approximately 

500 lbs and $67,000 to the weight and price of a 

comparable 15L diesel truck with 90 gallon 

tanks and required 140,000 miles per truck per 

year to reach 20% ROI. Adding an additional 35 

DGE tank increased the incremental cost to 

$103,000 and added another 700 pounds. 

Trucks with this additional tank required 

260,000 miles per truck per year to achieve a 

20% ROI. The best fit for operations using the 

HDPI engine are those with short range, high 

miles, and high horsepower requirements. 

Figure 27. Operational Characteristics that are Profitable, Marginally Profitable, and Not Profitable or Practical.

 Assumes a $1.50/ DGE fuel price differential between diesel and natural gas.
30

Importance of Fuel Price:

There seems to be a critical point in the price 

difference between diesel and natural gas 

where diesel is between $1.25 and $1.50 more 

expensive than natural gas per diesel gallon 

equivalent (Figure 28). At these prices, small 

changes in the price differential have a large 

impact on profitability. In other words, when 

the price differential is between $1.25 and 

$1.50/DGE, natural gas suddenly becomes 

profitable to a relatively large number of heavy 

truck operations when it was not profitable 

before.

When the price differential increases to above 

$2.00 per DGE, natural gas becomes attractive 

to an even greater number of fleets (those 

traveling 30,000 to 40,000 miles per year)

although the increase in the number of fleets is 

relatively less. At these higher diesel prices, 

factors such as the capital cost of the tractor 

and additional weight of the tractor have less of 

an impact on the minimum miles traveled to 

reach a 20% ROI threshold.

Even with very high priced diesel (price 

differential greater than $3.50 per DGE), there 

remains a bottom limit for an investment in 

natural gas trucks. Very low mileage fleets 

(those traveling less than about 20,000 miles 

per year) simply do not travel enough miles to 

reach a 20% return on their investment, unless 

the price of natural gas trucks decreases. Hybrid 

and electric trucks might better suit these types 

of operations.

At the other end of the spectrum, when the 

price differential between natural gas and 

diesel narrows to less than $0.75 per DGE

natural gas becomes impractical because the 

miles required to achieve 20% ROI exceed the 

miles that can possibly be driven by a truck in 

one year.

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

450,000

$0.75 $1 $1.25 $1.50 $1.75 $2.00 $2.25 $2.50 

Minimim Annual Miles per Truck

Additional Cost of Diesel over Natural Gas (per DGE) in Dollars 

Impact of Fuel Prices on the Minimum Annual Miles per Truck to 

Achieve a 20% ROI

Minimum Miles per Truck 

per Year Required for 20% 

ROI

LTL Pick Up & Delivery (CNG)

Farm Pick Up (CNG)

Farm Pick Up (LNG)

Line Haul 11.9L "Spark" (LNG)

Line Haul 15L HDPI (LNG)

Figure 28. Impact of Fuel Prices on the Minimum Annual Miles per Truck to Achieve a 20% ROI. 
31

Model Limitations and Alternative Approaches:

These conclusions (minimum number of miles 

per year per truck to be economically attractive) 

should be viewed as a rough estimate only. The

numbers will vary by company based on the 

desired return on investment, truck mission and 

utilization, the sensitivity of the operations to 

truck weight, the size of the tanks required to 

meet a given fuel range, and the capital 

investment of each alternative (price of each

truck).

There are limitations and alternative 

approaches to any model. For this paper, we 

used a Profit-and-Loss or Return on Net Assets 

(RONA) approach where the annual, pre-tax, 

pre-interest profit is divided into the 

depreciated, additional cost of a tractor over 

the life of that tractor. One alternative 

approach often used by a business to evaluate 

the attractiveness of an investment looks at 

after-tax cash flows over the life of the 

investment: Discounted Cash Flows Return On 

Investment (DCF-ROI). 

In contrast to the RONA approach the DCF-ROI 

approach considers the impact of taxes and the 

time value of money. Because the RONA 

approach is a pre-tax measurement, the 

threshold of minimum return should be higher 

than the threshold for minimum return on the 

DCF-ROI approach. For instance, if one used a 

minimum return target of 20% for RONA, and 

one assumed a 40% tax rate (combined federal 

& state), the equivalent after tax return 

threshold for the DCF-ROI approach would be 

12%.

While technically more correct from a finance 

perspective, we opted to use the RONA model

in this analysis because the RONA approach is 

easier to model and understand.

There is value in simplicity, particularly at this 

stage where fleets are asking whether or not it 

is worthwhile to further investigate and possibly

test a natural gas vehicle in their fleet rather 

than replace an entire fleet with natural gas 

trucks. Once a fleet gains some experience with 

natural gas trucks, then it might be more 

appropriate to use the more in-depth DCF-ROI

approach to see if it makes sense to convert an

entire fleet to natural gas. 

In the end, the decision to replace a fleet with 

natural gas trucks is not based on a model. It is 

based on the reliability and operational 

performance of the trucks and on actual savings 

seen in real tests of real trucks. 

Feedback from Lynden's People:

We expect the combination of accelerating 

demand in emerging markets for oil overseas 

and abundant domestic natural gas will keep oil 

prices high and natural gas prices low over the 

long term. Get used to gas. Whether we like it 

or not, and I can think of a lot of reasons why 

not, the future is going to be natural gas and 

batteries. - Jim J., CEO, Lynden Inc.

There are a lot of "con's". The only "pro" seems 

to be the price differential between natural gas 

and diesel. Without the model it is very hard to 

know the impact of all of these factors. But, 

there is value to looking at this. If we can get a 

competitive advantage, then it is worth it.

Weight is a huge concern because additional 

weight equates to loss of payload and 

additional miles (cost) to make up for lost 

revenue. If we could get a credit for the 

additional weight of running natural gas, this 

would eliminate the weight concern.

If we move forward with a natural gas vehicle, it 

will first involve a test in a lane where there is 

fuel. Lynden is still looking for the best place to 

test a natural gas vehicle: high miles, 

compatible with the 8.9L engine, and available 

fuel. If tests are successful and fuel becomes 

more available, then we may begin to purchase

natural gas trucks as old trucks are retired. 

- Alex M., Chief Operating Officer, Lynden Inc.

We may make a capital investment decision 

based on various issues, primarily oriented 

towards meeting a customer’s needs. From a 
32

financial standpoint, we may take one of two 

approaches. The RONA approach is a pre-tax 

measurement of earnings generated from the 

associated net assets. The DCF-ROI approach 

measures after tax cash flow returns on an 

associated investment. Regardless of which 

approach we take, the amount of risk we 

perceive in making the investment may 

influence our decision on what minimum return 

we will require. Companies who are successful 

over the long term will generally try to achieve 

a return on invested capital that exceeds their 

cost of capital, which varies by company. 

- Brad M. CFO, Lynden Inc.

This may make sense financially, but it also has 

to work from a practical standpoint. We don't 

know for sure if the 11.9L engine will work for 

us and fuel is not yet available for our routes. 

-Jason J., President, Brown Line

As the model points out, there could be huge 

potential. We need to look first at areas that 

have the highest miles and consume the most 

fuel per unit. The Farm Pick Up scenario is not 

necessarily the best choice because we do not 

know if the 8.9L will be approved for these 

kinds of weights, so we are looking at other 

scenarios. There is a lot to learn and many 

factors to consider so we need time to make a 

good decision. Lack of infrastructure means 

that we are limited to local routes rather than 

being able to respond to extraordinary events 

with our go-anywhere type fleet. We are always 

concerned with the first generation of any new 

engine (11.9 L Cummins-Westport in this case). 

As much as we like to lead our industry, the 

leading edge can be the "bleeding edge" if we 

rush. -Brad W., President, LTI Inc.

[After test driving a CNG 8.9L for 30 miles], the 

power of the truck was good considering it was 

an 8.9L engine. This wouldn't work for our 

operations, but the new 11.9L should work. 

The truck was quieter, you could hardly hear it

running. It burns clean, the exhaust was just

steam with no smell. The truck was heavy 

(16,000 lbs. compared to our 13,500 lbs. but 

was not set up with lightweight components. I 

wouldn't have a problem with driving these 

trucks in the future. Frank S. - Driver

From a maintenance perspective, there are a lot 

of unknowns (shop upgrades, maintenance 

technician training, shop tools, life of spark 

engines, tank issues, and safety concerns). 

Biogas is "neat", but without very expensive 

scrubbers, we can end up with a maintenance 

nightmare. Diesel is a stable technology and we 

understand it. Dave S. Director of 

Maintenance, LTI, Inc.

I had always thought that natural gas added a 

lot of weight, good to clear this up. We wethose (refuel on-site) to reduce man hours at the 

pump. This makes it challenging to test a truck 

without committing to a large investment (onsite refueling station) or sacrificing man hours 

to refuel elsewhere. Charlie M., Director of 

Maintenance, Lynden Transport

Lessons Learned from this Exercise: 

1. Look for lanes with high mileage, high 

fuel use per unit and available fuel for 

vehicle tests.

2. Don't "over spec" the tanks. These are 

very expensive and heavy, so should be 

spec'ed with the smallest tank practical 

to get required range.

3. Many dealerships are still learning 

about natural gas. California 

dealerships currently have more 

experience, especially with LNG trucks.

4. Make sure the tractor weight includes 

full fuel and urea for accurate weight 

comparison with diesel.

5. 2012-2013 is a logical time to invest in 

natural gas vehicles with the availability 

of the 11.9L spark ignited engine and 

infrastructure becoming available on 

major interstate corridors. 
33

6. Who is Currently Using Natural Gas and What Have They Learned?

CNG is being used successfully in short and 

medium range applications such as refuse 

trucks, straight trucks, and busses. Natural gas

in Class 8 tractors is only beginning to be 

adopted as LNG refueling infrastructure and 

larger natural gas engines are now beginning to 

become available.

There are currently about 1,800 natural gas

Class 8 tractors in operation in the United 

States, mostly in California, Arizona, and Texas. 

They primarily run "return-to-base" operations 

with a 150 mile radius because of limited 

infrastructure. Most (95%) operate on LNG and 

some (5%) on CNG. Figure 29 summarizes some 

of the current users of natural gas heavy trucks.

Business Year Location Natural Gas Truck Description Commodity Gov't Funding

Early Tests - Prototype

Liquid 

Carbonic

1994 TX 4 Freightliner LNG Detroit Diesel 

S60G Prototype

Natural Gas Yes

Norcal 2004 CA 14 Cummins-Westport GX LNG Solid Waste Yes

California-Based LNG and CNG

Total Trans

Services

2008 CA 8 Kenworth T800 LNG Drayage Yes

Ryder Systems 

Inc.

2011 CA 182 Freightliner M2 CNG 

20 Peterbilt LNG

Truckload Yes

Schneider 

National

2011 CA 4 Freightliner M2 CNG and LNG Truckload, LTL Yes

C.R. England 2011 CA 5 Kenworth T800 LNG 

Full service lease PacLease

Truckload, LTL No

UPS 2011 CA to 

NV

48 Kenworth T800 LNG (+11 

previously converted trucks)

LTL Yes

CNG Outside of California

Paper 

Transport

2010 WI to IL 7 Freightliner CNG 8.9L Truckload, LTL 5 of 7

Ruan 2011 IN, TN, 

KY

42 Kenworth T440 CNG biomethane

Full service lease PacLease

Raw Milk Yes

Foodliner 2011 IL 6 Freightliner M2 CNG Truckload Food Yes

Hribar Logistics 2011 WI 2 Kenworth T440 CNG Fly Ash Yes

Saddle Creek 

Corp.

2011 FL 40 Freightliner M2 CNG (130 DGE)

40 more in 2012

Truckload, LTL No

LNG Outside of California

TriMac 2008 TX, CA, 

AZ

43 to date 

14 Kenworth T800 LNG in 2010

LNG & Chemicals for 

Natural Gas Producers

Yes

Dillon 

Transport

2009 TX, OH 24 Peterbilt 384 LNG 8.9L Temperature sensitive 

bulk liquid tanker

Yes trucks

No station

Robert 

Transport

2010 QC 

(CAN)

180 Peterbilt 367 and 386 LNG 15L 

deployed over the next 3 years

Truckload, LTL No

EnviroExpress 2011 CN 18 Kenworth T800 LNG Incinerator Ash to 

landfill

Yes

Heckmann 

Corporation

2011 LA 200 Peterbilt 367 LNG on order Water for Natural Gas 

Producers

No

Vedder 

Transport

2011 BC 

(CAN)

50 Peterbilt 386 LNG Bulk Liquid and Dry 

Food

No

Sysco 2011 UT 9 Kenworth T800 Truckload Food Yes

Figure 29. Examples of heavy duty truck fleets using natural gas in North America.
34

Initial Tests:

Not surprisingly, some of the first businesses to 

test LNG are those who work closely with the 

natural gas industry. 

Liquid Carbonic, an LNG producer and 

distributor in Texas, worked with the National 

Renewable Energy Laboratory from 1994 to 

1997 in the first test to run LNG in a heavy 

trucks fleet. This test provided a valuable 

example showing that LNG could be used in 

heavy trucks. Operating costs were 

substantially higher at that time, but 

improvements to engines and price of 

equipment have improved dramatically since 

then.

TriMac hauls LNG and chemicals used in natural 

gas production. In 2008, they began testing 

three demo tractors in Houston and one in 

California. They took delivery of 19 more 

tractors in 2010; seven haul LNG on their 

California to Arizona lane, one hauls LNG in 

their Texas lane, and 14 work local lanes hauling 

chemicals. They now have a total of 42 LNG 

tractors. 

California-Based LNG:

California tax incentives and air quality rules 

have spurred the development of LNG 

infrastructure and adoption of LNG within the 

state. This has dramatically taken off in the last 

year with Ryder's natural gas leasing program 

and a new natural gas compliant maintenance 

facility in the state and a number of businesses 

who have taken advantage of state and federal 

grants. 

Ryder System Inc. joined the San Bernadino 

Associated Government's Natural Gas Vehicle 

Project to purchase 202 heavy duty natural gas 

vehicles, upgrade three natural gas compliant 

maintenance shops, and build two fueling 

stations. The CNG and LNG vehicles are now 

available for lease or rent. Ryder has secured 

lease agreements for 87 heavy duty natural gas 

trucks. Customers include Staples, Pacer 

international, and Golden Eagle Distributors, 

Inc.

Schneider is testing four Freightliner M2's with 

8.9L Cummins-Westport engines for use in 

California. Three are LNG and one is CNG. The 

trucks cost an up-charge of $30,000 to $40,000, 

most of which was covered by a California Air 

Resource Board (CARB) grant. They estimate the 

cost to upgrade their shop to be compliant with 

CALOSHA and FEDOSHA requirements for 

natural gas would cost approximately $1 million 

dollars per shop bay so they are outsourcing 

maintenance at this time. They expect an 11% 

increase in maintenance costs over diesel and a 

7%-10% reduction in fuel economy. 

C.R. England is leasing 5 Kenworth T800 LNG 

tractors under a full service lease from Paccar. 

The tractors will be used in their dedicated 

California refrigerated carrier operations.

LNG Outside of California:

Dillon Transport is currently running 14

Peterbilt 384 LNG bulk tankers based out of 

Dallas, Texas and has deployed 10 more in Lodi, 

Ohio. The Texas trucks haul 80,000 GVW liquid 

and industrial materials. Beginning in 2012 they 

will be used to haul product to a shingle roofing 

plant 125 miles away; each truck will make 2 

trips per day. The high volume and short range 

fits well with the LNG model.

Dillon chose to use the 8.9L spark engine rather 

than the Westport HD 15L because they are 

extremely weight sensitive and wanted to 

eliminate the extra diesel tank and diesel aftertreatment system required with the 

compression-ignited engine. They will be alpha 

testing the 11.9L spark ignited engine and think 

that this will be the right engine for the 80,000 

GVW loads, the 8.9L engine works, but is at its 

upper limit with these kinds of loads. 

They opted for LNG rather than CNG because 

the CNG would have required twice as much 

tank volume which would have been bulkier,

heavier, and more expensive. In addition, LNG 

refueling is as fast as diesel, whereas CNG "fastfill" stations will only fill quickly to 75%; the 

remaining 25% is filled as a trickle. They use an 
35

81 DGE LNG tank and are experimenting with 

dual LNG tanks for longer hauls. 

The main disadvantage of using LNG is that the 

trucks must get back to the station to refuel 

every night, "you can't just let a truck sit for 7 or 

8 days" because when the fuel warms up it 

turns to gas, builds pressure, vents out of the 

tank and evaporates. This is lost fuel. In 

addition, the tanks work better when they are 

cold, the first couple of refuelings take a long 

time as the tank cools and "gets seasoned". For 

high-volume, short range applications, LNG 

works great.

Dillon partnered with Clean Energy to build LNG 

refueling stations in Texas and Ohio. They are 

currently using mobile refueling stations (3,000 

DGE), provided by Clean Energy, until these 

stations are complete. Clean Energy has LNG 

plants in Willis, TX and Boron, CA. Fuel is 

trucked to fueling stations from those locations. 

Another potential source of LNG is local natural 

gas utility companies who sometimes store 

surplus natural gas as LNG during the summer 

months. 

Refueling the truck is different, but simple. The 

tank looks like a regular diesel tank on the side 

of a truck. It takes about five minutes to refuel. 

If the fuel drips, it just evaporates - there is no 

diesel spill. As a side- benefit, "no one can steal 

your fuel" as can be a problem with diesel.

The trucks were purchased from a California 

dealership because the California dealers were 

more familiar with the natural gas trucks and 

Dillon Transport hopes to be able to resell the 

vehicles more easily in California. They would 

have preferred to lease until the 11.9L engine 

became available, but leasing was not an option 

at that time (it is now).

Normally, Dillon does the maintenance for their 

trucks "in-house", but maintenance for the LNG 

trucks is outsourced to a dealer who is located 

very near their Texas terminal. They have run 

accelerated oil changes (every 10,000 miles) 

because of the severe duty cycle for these 8.9L 

engines, but plan to stretch this out to every 

12,000 miles. Drivers have had some anxiety 

over operating the new trucks and this 

sometimes manifests as maintenance concerns, 

but they have had no real issues with the 

trucks. 

They are happy to be using a domestic fuel, 

believe the national security message is 

important, and do a lot of work for oil and gas 

customers in Texas, but ultimately, this was a 

business decision based on the price differential 

of oil vs. natural gas. It has also added a new 

dimension to their customer relations as they 

can help customers save money and meet their 

sustainability goals. Customers are now asking 

for it in other locations.

Robert Transport is the first genuine for-hire 

long-haul LNG operation in North America. They 

currently have 10 LNG trucks in service and plan 

to add at least 180 more by 2014. The trucks 

are Peterbilt models 386 with the Westport GX 

(15L) engine and two 119 gallon LNG tanks (116 

DGE). The trucks run 600 miles between 

Mississauga, Ontario and Quebec City. 

Refueling infrastructure plans include three

sites between Mississauga and Quebec City.

Accelerated depreciation for natural gas trucks 

is 168% in Canada for a period of three years 

and helped justify the higher cost of the trucks. 

They needed to modify their repair garages in 

order to perform the maintenance on the 

trucks. Robert specs his trucks over a 10 year 

lifecycle. The trucks cost close to $225,000. 

They expect to break-even with the current fuel 

prices and save money over the long term as 

the price differential between natural gas and 

diesel diverges. 

CNG in Close- Loop Applications:

Outside of California, natural gas use in heavy 

trucks has so far been limited to "closed-loop"

applications, because LNG infrastructure is not 

yet available. In these operations trucks travel 

out and back to return to a "home" terminal or 

fueling station to refuel. CNG, however, is being 

used in both closed-loop and dedicated lane 

operations with ranges up to 350 miles. More 

tanks can provide even larger ranges but are 

heavy and expensive. 
36

Paper Transport currently runs seven 

Freightliner CNG trucks with the CumminsWestport 8.9L engine between Green Bay, 

Wisconsin and Chicago, IL. They are currently 

able to operate in a 300 to 350 mile range with 

the five 15 DGE CNG tanks mounted in the 

"behind the cab" configuration, but plan to add 

another 40 DGE side-rail mounted tank to 

further increase their range. The incremental 

cost of the trucks is approximately $50,000 and 

fuel savings are between $1.60-$2.90 per 

gallon. Maintenance costs are substantially 

higher because they are running the trucks 

significantly more miles than what they are 

designed for. Upgrades to the shop were not 

necessary because maintenance is contracted 

out to Cummins. They do not consider weight 

to be an issue, because the day cab is light and 

the engine is smaller and lighter than what they 

would normally use. Normally, Paper Transport 

would use a more powerful 13L or 15L engine 

for their 80,000 pound payload. The CumminsWestport 8.9L ISL-G engine works well on the 

flat terrain in the Midwest, but would not be 

practical with this payload on hills of any 

significance. They have had no issues with the 

fuel or trucks and are "getting everything that 

they hoped." They received a Clean Cities grant 

for five of the seven trucks that they now 

operate and plan to add additional trucks in the 

future. Some will be the 8.9L engines, but most 

will be the 11.9L engines when they become 

available. Jeff Shefchik, President, says that the 

driving factors in using natural gas are 

economics (fuel savings), the environmental 

benefit, and the fact that natural gas is an 

American fuel and supports the U.S. economy. 

Ruan, a bulk food transporter, and Fair Oaks 

Dairy farm recently announced the largest 

renewable CNG project in the United States. 

Ruan is running 42 Kenworth T440 CNG trucks 

with two 40 DGE side-rail tanks and 55 DGE

mounted back of cab (600 mile range), the 8.9L 

Cummins-Westport ISL-G engine, and Allison 

3000HS six-speed automatic transmission. The 

tractors’ specifications are able to handle the

80,000-lb gross combination weight, though at 

its upper limit. The trucks are operated under a 

full service lease from PacLease. 

The trucks haul raw milk from Fair Oaks Farms 

to processing plants in Indianapolis, Indiana, 

Kentucky, and Tennessee. The Indiana routes 

are "out-and-back", but the Kentucky and 

Tennessee routes are beyond the range of the 

fuel carried on board, so "relay-operations", 

where a driver hands off his entire rig, are 

required. The southbound driver with a load of 

milk trades off with a northbound driver 

transporting an empty milk trailer. The 

southbound driver takes the empty trailer back 

to Fair Oaks Farms, while the northbound driver 

takes the full load of milk south for delivery to 

the processing plants.

Federal and state grants helped offset the 

higher cost of the CNG tractors and the cost of 

building two CNG filling stations. In order for it 

to make financial sense, each tractor needs to 

get about 250,000 miles per year. Fair Oaks 

Dairy personnel preload the tank trailers for the 

Ruan drivers to reduce down-time at the farm. 

The tractors weigh about 17,000 pounds with 

lightweight disc wheels, brake drums, air tanks, 

fifth wheels, jacketing, milk tankers, and 

eliminating the product pumps.

Fair Oaks Farms operates four bio-digesters that 

produce methane from cow manure. One of 

these digesters will supply methane to the new 

CNG filling station at Fair Oaks. As part of this 

project, another filling station was built 220 

miles away as part of a State of Indiana effort to 

create a CNG corridor on I-65.

Saddle Creek Corporation has agreed to 

purchase 40 Freightliner M2 trucks in 2011 and 

40 more in early 2012 for their Florida fleet. 

The trucks will use two 25 DGE CNG tanks 

behind the cab and two 40 DGE rail-mounted 

tanks and expect a usable range of 560 miles. 

President Mike DelBovo says, "because the cost 

of natural gas is less volatile than diesel, it 

allows us to have more control over our fuel 

costs and our customers to have a more stable 

fuel surcharge".
37

7. Policy Options to Support the Adoption of Natural Gas Heavy Trucks

1. Weight Exclusion. Trucks are limited to a 

certain Gross Vehicle Weight (GVW) on a given 

roadway. Any additional weight to the truck

(e.g. natural gas fuel tanks) reduces the payload 

that they can carry. Fleet managers are 

constantly looking for ways to minimize weight 

and maximize payload. 

A weight credit for the additional weight of 

natural gas truck fuel tanks would eliminate the 

concern and financial impact of a diminished 

payload. A credit for the empty weight of the

CNG or LNG tanks would be easiest to 

determine because weight differential varies 

greatly depending on the diesel truck that is 

used for comparison. This would translate to a

slight payload benefit for using natural gas

because the natural gas itself is lighter (per Btu)

than diesel and natural gas trucks do not 

require diesel after-treatment systems. This 

would hold no benefit for operations that are 

not weight sensitive (Pick Up and Delivery 

modeled here). Figure 31 shows a possible

weight credit for various tank configurations.

2. Eliminate the Federal Excise Tax (FET) for 

Natural Gas Heavy Trucks: Federal Excise Tax 

accounts for roughly 10% of the incremental 

cost of a heavy duty natural gas truck. An FET 

exclusion for natural gas trucks reduces the high 

capital cost of the truck and makes an 

investment in natural gas trucks much more 

attractive. This would not impact trucks less 

than 33,000 GVW because they do not pay FET.

3. Ensure a minimum $1.25-$1.50 price 

differential between diesel and natural gas. A 

policy that maintains this critical price 

differential would ensure that the price spread 

between diesel and natural gas does not narrow 

below a point where it is not profitable for most 

fleets to invest in a fleet of natural gas trucks. 

(Figure 28). It would also reduce concern and 

risk associated with a large capital investment in 

natural gas vehicles followed by a narrowing in 

the price differential. 

This policy could be an extension of the 

$0.50/DGE tax credit, although this would need 

to be guaranteed for at least 5 years to ensure 

confidence. A more effective approach could 

take the form of a "feebate" where a "fee" on 

oil pays for a natural gas "rebate" - this could be 

written to take effect only if the price 

differential between diesel and natural gas falls 

below the sensitive $1.50 per DGE level. 

4. Tax Credits and Grants for Infrastructure and 

Vehicles. A tax credit for the additional cost of a 

natural gas tractor reduces the high cost and 

associated risk of investing in natural gas. Tax

credits are not necessary to make an 

investment in natural gas attractive for high 

mileage fleets if the current price differential 

between natural gas and diesel persists. 

However, an 80% tax credit (as proposed in the 

NATGAS Act HR 1380 and S 1863) will 

accelerate the adoption of natural gas by high 

mileage fleets and make it attractive to lower 

mileage fleets.

The high capital cost to upgrade maintenance 

shops to be safe and compliant remains a 

financial and operational barrier. There are 

currently very few natural gas compliant shops 

available to service natural gas vehicles and it is 

not always practical or cost effective to travel 

long distances for maintenance. A tax credit for 

upgrades to natural gas maintenance garages 

would help mitigate this issue.

6. Access to Capital. The incremental cost of 

natural gas trucks is high because of the 

specialized tanks required. Most fleets have 

limited access to capital to make this 

investment. Banks may be unlikely to lend for 

new technologies like natural gas vehicles. In 

the absence of grants and tax credits, low 

interest loans would help fleets overcome this 

hurdle.

7. Biogas Support. The environmental benefit 

of using biogas (farm waste, wastewater 

treatment, and landfill gas) natural gas as a 

transportation fuel arguably justifies additional 
38

government support. Box 2 discusses biogas in 

more detail; Box 3 discusses other alternative 

fuel technologies.

Biogas is one of the least expensive renewable 

sources of energy. It is cheaper than gasoline 

and diesel, but more expensive than fossil 

sourced natural gas due to the high cost of 

purification. It is not likely to be able to 

compete with low-priced fossil sourced natural 

gas prices without monetizing its environmental 

benefit. Again a "feebate" could be used where 

a fee on fossil sourced natural gas and/or oil 

would pay for a rebate on biogas to make it cost 

competitive with fossil sourced natural gas.

Figure 30 shows the estimated impact of 

policies on the minimum number of annual 

miles per truck to be economically attractive. 

- With no policy changes, natural gas makes 

sense for high mileage trucks (>90,000

miles/year). 

- Natural gas becomes attractive for lower 

mileage trucks (40,000-50,000 miles/ year) with

a $0.50 per DGE tax credit for natural gas.

- A Federal Excise Tax Exclusion for natural gas 

vehicles reduces the minimum number of miles 

to between 30,000 and 50,000.

- A weight exclusion for the empty weight of 

CNG and LNG tanks would lower the minimum 

number of miles to include trucks traveling 

53,000-63,000 miles per year, with a larger 

benefit for CNG. This would not benefit 

operations that are not weight sensitive.

- Combined, these policies would make natural 

gas attractive for trucks traveling 25,000 to 

35,000 miles/ year.

- Alternatively, an 80% tax credit for the 

additional cost of a natural gas truck makes a 

spark-ignited natural gas truck attractive for low 

mileage fleets (those traveling around 15,000 

miles/ year). It also becomes attractive for 

trucks with higher power requirements (HDPI 

15L) traveling at least 25,000 miles per year.

Figure 30. Estimated Impact of Suggested Policies on the Minimum Number of Annual Miles 

per Truck to Achieve 20% ROI. Assumes $1.50 price differential for base case (Diesel $4.00/ 

gallon; Natural Gas $2.50 / DGE). Farm Pick Up and Line Haul are weight sensitive operations. 

Pick-Up and Delivery is not weight sensitive.
39

Figure 29. Proposed Weight Credit for Natural Gas Fuel Tanks (empty weight).

Box 2. Renewable Natural Gas: Bio-methane and Biogas.

Tank Configuration Weight Credit for Empty Tank

CNG (5) 15 gallon back of cab (75 DGE) 1,650 lbs

CNG (2) 40.5 gallon side rail mounted (81 DGE) 1,200 lbs

LNG (1) 119 gallon side rail mounted (60 DGE) 800 lbs

LNG (1) 150 gallon side rail mounted (75 DGE) 1,000 lbs

Biomethane or "biogas" is very attractive from an environmental perspective. Methane that would 

otherwise enter the atmosphere as waste from farms, landfills, and wastewater facilities can be used as a 

fuel in natural gas engines, thereby removing a methane source and displacing a fossil fuel source at the 

same time. Methane is 25 times more potent as a greenhouse gas than CO2, so using it as a fuel dramatically 

reduces greenhouse gas emissions. It also allows fleets to partner with customers' sustainability initiatives 

by using their waste as a fuel.

Biogas, like fossil sourced methane, can be used in natural gas vehicles. Biogas has been used successfully in 

natural gas powered refuse trucks (landfill gas) for many years and more recently in trucks hauling milk (dairy 

farm waste). The perfect application for a biogas fueled truck is a return to base fleet that returns to the site 

of biogas production. As with any fuel, fuel quality must be ensured in order to avoid maintenance problems. 

Various processing techniques are used to "scrub" the biogas and remove impurities in order to bring the 

fuel to above pipeline quality. There is no warranty issue with using biogas in a natural gas engine. 

Biogas is less expensive (per Btu) than other renewable fuels (solar and wind), but more expensive than fossil 

natural gas. A program called "RNG-10" under development by Clean Energy is designed to bring biomethane to market at a more competitive price. Fleets willing to pay 10 cents more for natural gas will get 

credit for fueling their vehicles with biogas and cover the cost of biogas production elsewhere. This allows 

fleets that are not able to refuel with biogas directly to indirectly fuel their fleet with renewable biogas and 

reduce GHG emissions by 80-90%. This program can easily transfer to an optional surcharge for shipping 

customers interested in "green transportation" for their goods.

Figure 31. Proposed Weight Credit for Natural Gas Fuel Tanks (empty weight). 
40

Box 3. Other Alternative Fuel Technologies.

OTHER ALTERNATIVE FUEL TECHNOLOGIES: 

Hydrogen is considered the ultimate zero emissions, domestic, and renewable fuel. It can be generated by 

running an electrical current through water, splitting it into water and hydrogen. The electrical current can 

come from renewable sources of energy (solar, wind, landfill gas, or photosynthesizing microbes) and is 

sometimes thought of as a "battery" for its ability to store intermittent renewable sources of energy to be 

used later as fuel. More commonly, is it made from natural gas in a process called "steam-reformation" in 

which high pressure steam reacts with natural gas to form "synthesis gas" which then reacts with water to 

form hydrogen. When burned as a fuel, hydrogen emits only oxygen, water, and very few NOx emissions. 

However, the high cost of production and vehicles means that hydrogen is at least a decade away from being 

commercially viable as a transportation fuel.

Hydrogen, as a transportation fuel, is faced with similar, or even more challenging issues than natural gas. 

1.) It is less dense (Btu/gallon) so must be stored at even higher pressures (10,000 psi) or colder (-432 ̊ F) 

temperatures at high pressure in heavier, more expensive tanks. Hydrogen has the potential to be stored 

without tanks as a Polymer Electrolyte Membrane (PEM) where hydrogen atoms chemically bond to 

materials for storage, but this technology is still in the research and development phase. 2). It faces similar 

refueling infrastructure issues. 3.) It is more flammable than natural gas, so faces even more challenging 

safety issues. 

Natural gas is considered to be the "technological bridge" to hydrogen because advances in natural gas 

vehicles, tanks, refueling infrastructure, safety solutions, workforce training, and business alliances directly 

or indirectly apply to hydrogen, lower the hurdles that must be overcome, and move it closer to being 

economically viable. For example, natural gas engines can burn a compressed hydrogen/CNG blend with 

only minor modifications; tanks used to store hydrogen use the same base technology as natural gas CNG 

and LNG tanks; shops that are upgraded to comply with natural gas safety guidelines, are well on their way 

to being hydrogen compliant as well; natural gas refueling infrastructure has the potential to be modified to 

fulfill hydrogen refueling needs and paves the way for similar permitting and business relationships; and as 

people begin to understand natural gas, hydrogen becomes easier to accept.

Hydrogen is not a near-term solution to our transportation energy needs, but will become economically 

feasible more quickly because of the technological and infrastructure advancements that will come with a 

transition to natural gas.

Hybrid-Electric Vehicles work best for low speed operations with frequent stops or engine idling such as incity pick-up and delivery vehicles and service vehicles. They are not a practical solution for on highway heavy 

trucks because fuel efficiency gains are minimal at high speeds (> 35-45 mph) with little stop-and-go.

During braking, energy is captured and stored in the batteries (or in the case of hydraulic hybrids, stored as 

hydraulic pressure). This energy can be used exclusively to power the truck during take-off, power electrical 

equipment without engine idle, and to supplement diesel power during acceleration. This "regenerative 

braking" also extends brake life.

Hybrid tractors are usually used for applications below 33,000 GVW, but in some cases have been approved 

for up to 54,000 GVW. The incremental cost of a hybrid delivery tractor is similar to or slightly less than a 

natural gas tractor. The main benefit comes from a higher fuel economy (15-30%) compared to diesel in 

stop-and-go situations. 

Payback on a hybrid vehicle depends on the amount of stop and go, time spent at low speeds, and time 

spent at idle, but under the right conditions, a hybrid truck can be a better alternative than natural gas. 
41

8. Conclusions

This is an exciting time for heavy-duty natural 

gas trucks.

1. Refueling infrastructure is finally 

underway. Clean Energy and Flying J-Pilot 

have partnered to build a foundational grid 

of LNG fueling stations for heavy -duty 

trucks along major interstate corridors, with 

$300 million dollars invested in this project. 

Plans are in place to have 80 new stations 

opened along coast-to-coast corridors by 

December 2012. They anticipate having an 

LNG filling station every 200-300 miles on 

major highways by June 2013 and 300-400 

stations serving all regional routes by 2015. 

2. The price spread between natural gas and 

diesel has reached a tipping point where 

natural gas has suddenly become profitable 

to a large number of heavy truck 

operations. High mileage fleets (those 

traveling 60,000-90,000 miles per truck per 

year) see an attractive ROI from fuel cost 

savings, even when considering

maintenance costs, fuel economy penalty, 

loss in payload from additional weight of 

the tanks, and the higher cost of the 

tractor. This is true for both CNG and LNG 

trucks, but only for the lower cost sparkignited engines. Existing compression -

ignited engines are restricted to very high 

mileage fleets (140,000 miles per truck per 

year).

3. The "game changer" 11.9L spark-ignited 

engine will be available in the first quarter 

of 2013. This engine will fit a much larger 

number of class 8 truck operations than the 

existing 8.9L spark engine which was 

designed for refuse trucks and transit 

busses. It will not need the heavy diesel 

after-treatment technology and will offer a 

much more cost effective, lighter weight, 

higher fuel capacity alternative to the 

existing 15L compression-ignited engine. 

Also in 2013, the Navistar 13L dual-fuel 

engine will be entering test phases.

However, a handful of barriers still remain

to the mainstream adoption of natural gas 

by heavy truck fleets.

1. Refueling infrastructure is still limited 

compared to diesel. Even with 300 new 

LNG refueling stations, fleets will be limited 

to routes where fuel is available. This 

means fleets using dedicated natural gas

engines must sacrifice their ability to "go 

anywhere" to meet customer needs.

2. Natural gas trucks are substantially more 

expensive than a diesel truck. This is 

primarily due to the cost of the specialized 

CNG and LNG fuel tanks. This is a significant 

barrier to fleets and owner-operators with 

limited access to capital.

3. The high capital cost of upgrading a 

maintenance shop remains a factor that 

can make an investment in natural gas 

trucks considerably less attractive. Full 

service leases or maintenance packages are 

available, but this is not always practical for 

fleets in rural areas and is generally less 

desirable than performing maintenance "inhouse."

4. Operating range is limited by the tanks 

that can fit on a truck at an economical 

price. This is generally the 75 DGE 

configuration (LNG ) and 40 DGE side rail or 

75 DGE back of cab (CNG). Although it is 

possible to fit 150 DGE (LNG, "spark" 

engine), 143 DGE (CNG, "spark" engine), 

and 116 DGE (LNG HDPI 15L) on a truck, the 

high cost of the additional tanks decreases 

the financial payback substantially. This 

means that until infrastructure is widely 

available, fleets will be limited to routes 

where fuel is available and centrally-fueled 

operations. 

5. LNG use is limited to operations where 

trucks are refueled every 1-2 days so that 

venting of fuel is not an issue. This is not 

likely to be a large problem because natural 
42

gas trucks do not make financial sense for 

low mileage fleets. 

6. Fleets are apprehensive about new "high 

risk" technology. It takes time to learn 

about and carefully test a new kind of truck 

and fuel.

Despite these barriers, if oil prices remain high 

and natural gas prices remain low and stable, 

then high mileage fleets are likely to initiate 

tests of natural gas trucks where infrastructure 

is available in the next few years, even without 

government subsidies. If those tests are 

successful, then they will begin to purchase new 

natural gas trucks as old trucks are retired. Tax 

incentives can help accelerate this transition 

and make natural gas attractive to lower 

mileage fleets.

1. A weight exclusion for the additional 

weight of natural gas tanks would 

eliminate concern and cost associated 

with a loss of payload. 

2. A Federal Excise Tax exclusion for 

natural gas trucks would reduce the 

incremental cost of a natural gas truck 

by around 10%. 

3. A policy that ensures a $1.25-$1.50 

price differential between natural gas 

and diesel would ease concern over the 

risk of a narrowing price spread and 

maintain a critical price difference for 

fleets who invest in natural gas trucks 

to achieve a desired ROI . 

4. Tax credits for the additional cost of 

natural gas vehicles would help 

accelerate the transition to natural gas 

and make natural gas attractive to 

lower mileage fleets. This could be paid 

for via fuel tax.

5. Tax incentives or grants for upgrades to 

maintenance shops that service natural 

gas vehicles would help alleviate the 

high capital cost and practical issue of 

being able to maintain a fleet of natural 

gas vehicles.

6. Low-interest loans would help fleets 

with limited access to capital make the 

investment in natural gas trucks. 

7. Support for biogas would help make 

this renewable, low carbon fuel cost 

competitive with fossil sourced natural 

gas.

In summary, conditions are right for many high 

mileage fleets to begin investing in natural gas 

in the next few years as refueling infrastructure 

expands, more engine options become

available, and the price differential between 

natural gas and diesel remains persistent.

The most attractive fleets are those with high 

miles (>60,000-90,000 miles/truck per year),

that have fuel available within a 350-450 mile

operating range, and that have operations 

compatible with a spark-ignited engine (7.6L, 

8.9L, or 11.9L) or very high miles (>140,000 

miles per truck per year; 15L HDPI). 

This is likely to be a gradual process that 

accelerates in Q1 2013 as two of the primary 

barriers: 1.) lack of infrastructure and 2.) 

limited engine options, see major 

breakthroughs. Where refueling infrastructure 

is available, fleets are likely to initiate tests of 

natural gas trucks and if these tests are 

successful (i.e. profitable and reliable), then 

fleets will begin to replace older diesel trucks 

with natural gas trucks through attrition. 

Policy incentives that address remaining 

barriers: 1.) the high incremental cost of 

natural gas trucks, 2.) uncertainty over the cost

and requirements of upgrades to maintenance 

shops, and 3.) the additional weight of natural 

gas fuel tanks would help mitigate these 

barriers and accelerate the transition to natural 

gas by heavy truck fleets. 

Policy that is timed to coincide with the Q1 

2013 release of the 11.9L engine and expanding 

refueling infrastructure would have the greatest 

impact by removing uncertainty over potential 

future policy and adding to the growing 

momentum of interest in natural gas as a 

transportation fuel. 
43

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Appendix

Figure A-1. Fire Codes Related to Natural Gas Repair Garages and Fuel Systems.