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Multi-Pollutant Emissions Benefits of Transportation Strategies-FHWA

5. Vehicle, Fuels, and Technology Strategies

Vehicle, fuel, and technology projects and programs are designed to change the emission rates of vehicles either by changing the fuel being used, the type of vehicle or emissions control technology, or a combination of both. Some programs also focus on eliminating gross polluters, or vehicles whose emissions controls have failed, or on controlling specific types of emissions (e.g., road dust). The methodologies for these strategies generally involve estimating the number of vehicles affected, and then calculating the change in the emissions factors based on changes in vehicle stock or equipment. These strategies, and associated methodologies, are presented below.

21. Idle Reduction Facilities

Strategy Overview

Long haul truck drivers will often rest for extended periods in their sleeper compartment, during which time they idle the engine to operate air conditioning, heat, or on-board appliances, such as televisions. An idle reduction technology consists of the use of an alternative energy source in lieu of using the main truck engine for the purpose of reducing long duration truck idling. Some of these technologies are mobile and attach onto the truck (mobile auxiliary power units (APUs)), and provide air conditioning, heat, and electrical power to operate auxiliaries such as a microwave. Another technology involves electrifying truck parking spaces (stationary truck stop electrification (TSE)) with or without modifying the truck. In general, this involves power from the electrical grid providing energy to operate stationary equipment or on-board truck equipment to provide cab heating, cooling, and other needs. The EPA defines long duration idling as the operation of the truck's propulsion engine when not engaged in gear for a period greater than 15 consecutive minutes.

Emissions Impacts

Measures to reduce long duration truck idling should result in reductions in all pollutants, as shown below in Table 5-1. However, EPA's guidance documents only provide emissions factors for NOX and PM. Given that heavy-duty trucks make up a disproportionately large share of the on-road vehicle emissions inventory for NOx and PM, this strategy will be most effective in reducing these pollutants.

Table 5-1. Idle Reduction Facilities - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

decrease

decrease

decrease expected

decrease

decrease expected

decrease expected

decrease expected


(-) = Decrease expected, but not quantified in EPA guidance

General Considerations

The level of emissions impact depends on:

Additional considerations include the possibility that demand for the facilities will change. In some situations, the truck stop will experience an increase in the number of vehicles in response to the improved efficiency and comfort of the rest area, or utilization may decrease if too many trucks are not equipped to take advantage of the external power.

For EPA guidance, see "Guidance for Quantifying and Using Long Duration Truck Idling Emission Reductions in State Implementation Plans and Transportation Conformity," http://epa.gov/cleandiesel/documents/420b09037.pdf.

Sample Project

Truck Stop Electrification

This project proposes to electrify a single truck stop43 .The project includes the following inputs:

The project was analyzed using the following sketch planning methodology, assuming that each electrified parking space is used in a similar manner.

Step 1: Estimate daily hours of truck idling reduced.

Truck idling hours reduced
= (Number of TSE truck stops) x (average number of truck parking spaces utilized) x [(average daily idling hours per truck) -
(estimated daily idling hours per truck with project)]
= (1) x (100) x [(10) - (2)]
= 800 hours per day

Step 2: Calculate annual idling emissions reduced.

Truck idling emissions reduced
= (Daily hours of idling reduced) x (idling emission factor)
= (800 hrs) x (idling emissions factor)

Note: If a mobile idle reduction technology is used, the additional emissions from the mobile idle technology must be considered, and net emissions reductions calculated.

Emissions impacts from this sample are shown below.

Table 5-2. Total Emissions Reduced (tons/year) from Truck Stop Electrification Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

6.48

6.48

NA

238

NA

NA

NA

2010

3.81

3.81

NA

238

NA

NA

NA

2020

0.88

0.88

NA

238

NA

NA

NA

*Emission factors for PM-2.5, PM-10, and NOx were provided by EPA document, "Guidance for Quantifying and Using Long Duration Truck Idling Emission Reductions in State Implementation Plans and Transportation Conformity."

22. Accelerated Retirement/Replacement of Buses

Strategy Overview

Bus replacement projects accelerate the replacement of older buses with new vehicles which emit fewer pollutants and often use alternative fuels such CNG, LNG, electric, or hybrid electric. These new, less polluting vehicles run along existing routes, and therefore, do not change vehicle mileage or service levels.

Emissions Impacts

Accelerated retirement of older, more polluting buses will reduce emissions of various pollutants, notably NOx and PM. The specific pollutants that are reduced will depend on the fuel type and technology of the replacement vehicle; some replacements have no known effects on some pollutants. General emissions impacts from the strategy are shown below.

Table 5-3. Accelerated Retirement/New Purchase of Buses - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

decrease

decrease

decrease

decrease

decrease

decrease

decrease

Note: Impacts will vary based on type of replacement vehicle. Some vehicle types have no quantified benefits on some pollutants.

General Considerations

The level of emissions impact is greatly affected by the type of replacement bus. Bus emission factors, which will vary by the age of bus, the size of the bus, the mileage on the engine and the travel speed. The level of emissions impacts for different types of buses also differs based on when the program is implemented. For instance, a 2006 CNG bus emits less CO and NOx than a 2006 diesel bus; however, due to substantial improvements in diesel emissions factors, a 2010 diesel bus produces less CO and NOx than a CNG bus.

Emissions impacts are affected by the following factors:

Emissions reductions that come from replacing an older vehicle with a newer, cleaner vehicle will not provide emissions reduction credit longer than the period of time that the older vehicle would have been kept in service without the replacement program.

For more information, see EPA's Diesel Retrofit SIP and Conformity guidance see http://www.epa.gov/cleandiesel/publications.htm and EPA's National Clean Diesel Campaign http://www.epa.gov/cleandiesel.

Sample Project

Urban CNG Bus Purchase

A transit agency proposes to purchase a new 2005 CNG bus instead of a new diesel bus.44 The new CNG bus is not included in the transit agency fleet average used to determine compliance with the Air Resource Board transit bus fleet rule. Project specifics are as follows:

Step 1: Calculate baseline bus emissions

= [(Emissions standard) x (conversion factor 4.3 bhp-hr/mi)] x (annual mileage) x (conversion factor ton/907,200g)
= [NOx (2.00g/bhp-hr) x (4.3 bhp-hr/mi)] x (50,000 mi) x (ton/907,200g)
= 0.47 tons/yr NOx
= [PM-10 (0.01g/bhp-hr) x (4.3 bhp-hr/mi)] x (50,000 mi) x (ton/907,200g)
= .002 tons/yr PM-10

Step 2: Calculate new bus emissions.

= [(Emissions standard) x (conversion factor 4.3 bhp-hr/mi)] x (annual mileage)
x (conversion factor ton/907,200g)
= [NOx (0.96g/bhp-hr) x (4.3 bhp-hr/mi)] x (50,000 mi) x (ton/907,200g)
= 0.23 tons/yr NOx
= [PM-10 (0.01g/bhp-hr) x (4.3 bhp-hr/mi)] x (50,000 mi) x (ton/907,200g)
= .002 tons/yr PM-10

Step 3: Calculate the total annual emissions reduction.

= (Baseline emissions) - (new emissions)
= [NOx (.046) - (0.23)] = 0.24 tons/yr NOx
= [PM-10 (0.01) - (0.01)] = 0.0 tons/yr PM-10

Table 5-4. Emissions Reduced (tons/year) from Purchase of New Bus Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

NA

<0.01

NA

0.24

NA

NA

NA

Emissions benefits are not calculated for 2010 and 2020, due to lack of availability for emissions factors from EPA guidance, as well as in consideration of the anticipated useful life of vehicle replaced.

23. Accelerated Retirement/Replacement of Heavy-Duty Trucks

Strategy Overview

Replacement projects for heavy-duty vehicles accelerate the retirement of older engines that are less efficient and emit more pollutants. New vehicles which emit fewer emissions may be conventional diesel vehicles, or use alternative fuels for power such CNG, LNG, electric, or hybrid electric. Accelerated retirement programs can be of two types: Fleet wide projects refer to situations where there are general mandates or goals, but the number of individual vehicles or engines which will be replaced is not known in advance. Alternatively, fleet specific replacement projects target a well defined group of vehicles which can encompass multiple model years, vehicle types, or equipment types. This type of program is often implemented by a private company with a diverse vehicle fleet. While fleet wide projects will target a particular engine or heavy duty vehicle type with known emissions levels, a fleet specific strategy will have a precise number of vehicles or engines in each model year of each class that will be replaced or retired, and a more accurate emissions estimate can be developed.

Emissions Impacts

Accelerated retirement of older, more polluting heavy-duty vehicles will reduce emissions of various pollutants, notably NOx and PM. The specific pollutants that are reduced will depend on the fuel type and technology of the replacement vehicle; some replacements have no known effects on some pollutants. General emissions impacts from the strategy are shown below.

Table 5-5. Accelerated Retirement of Heavy-Duty Vehicles - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

decrease

decrease

decrease

decrease

decrease

decrease

decrease

Note: Impacts will vary based on type of replacement vehicle. Some vehicle types have no quantified benefits on some pollutants.

General Considerations

The level of emissions impact depends on:

For more information, see EPA's Diesel Retrofit SIP and Conformity guidance see http://www.epa.gov/cleandiesel/publications.htm and EPA's National Clean Diesel Campaign http://www.epa.gov/cleandiesel.

Sample Projects

Sample 1: Replacement of 1990 and Earlier Model Long Haul Trucks

This example assumes that 1990 and earlier model year long haul Class 8B trucks will be replaced with 2006 model year vehicles. Assumptions include:

Step 1: Calculate mileage affected.

= (Number of trucks) x (average mileage per year)
= 20 trucks x (50,000 miles)
= 1,000,000 miles per year

Step 2: Calculate reduction in emissions.

= (Mileage affected) x [(1990 emissions factor) - (2006 emissions factor)]

Table 5-6. Total Emissions reductions (tons/year) from New Heavy Duty Truck Purchase Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

0.34

0.47

3.30

18.74

0.89

<0.01

<0.01


Emissions benefits are not calculated for 2010 and 2020, due to lack of availability for emissions factors from EPA guidance, as well as in consideration of the anticipated useful life of vehicle replaced.

Sample 2: New purchase of a LNG heavy duty truck in place of a traditional diesel engine vehicle

This sample is based on a project in California, whose parameters include:45

Step 1: Estimate the number of heavy-duty vehicles expected to participate, accounting for the design of the program, and other local factors.

Step 2: Calculate the daily VMT for the heavy-duty vehicles replaced through the program.

= (Number of vehicles replaced) x (average daily VMT)
= 5 x 100,000 miles

Step 3: Calculate the expected emissions reductions as a result of the strategy.

= [(Emission factor from old engines) - (emission factor from new engines)]
x (vehicle VMT affected)

Table 5-7. Total Emissions Reductions (tons/year) from New Heavy Duty Truck Purchase Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

0.02

0.04

0.69

NA

0.16

NA

NA


Emissions benefits are not calculated for 2010 and 2020, due to lack of availability for emissions factors from EPA guidance and in consideration of the anticipated useful life of vehicle replaced.

24. Diesel Engine Retrofits

Strategy Overview

A diesel engine retrofit project includes the addition of any technology, device, fuel or system that achieves emissions reductions beyond that currently required by EPA regulations at the time of its certification. Diesel engine retrofit technologies can be applied to both to on-road vehicles and non-road engines. Policies and programs available to state and local governments include mandatory fleet retrofits, government contracting requirements, and voluntary programs with funding options. There are a range of technologies which can be used to retrofit heavy duty diesel vehicles, including particulate filters, oxidation catalysts, flow through filter, crankcase filters, NOx reducing catalysts, and exhaust gas recirculation (EGR). As each technology will impact emissions levels differently, these differences should be reflected in the emissions reduction calculation and input data.

Emissions Impacts

Emissions reductions by pollutant will depend on the type of retrofit technology. Some are designed primarily to reduce NOx, while others are designed to reduce PM.

Table 5-8. Diesel Engine Retrofits - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

decrease expected/no effect

down arrow / N

decrease

down arrow / N

decrease

no effect

no effect


Note: Impacts will vary based on type of retrofit technology applied.
(-) = Decrease expected, but not quantified in EPA guidance; N = No effect; not quantified in EPA guidance (will vary based on type of retrofit technology applied)

General Considerations

Factors affecting emissions impacts include:

EPA recommends using the National Mobile Inventory Model (NMIM) to estimate emissions reductions from retrofit projects for SIPs and conformity analyses. Fleet wide projects refer to situations where there are general mandates or goals, but the actual individual vehicles or engines which will be retrofit are not known in advance. Alternatively, fleet specific retrofit projects target a well defined group of vehicles which can encompass multiple model years, vehicle types, or equipment types. There are important differences between fleet specific and fleet wide projects that affect the kind of information that is needed to run NMIM. It is assumed that for fleet specific projects the precise number of vehicles or engines in each model year of each class that are to be retrofit will be known. In addition, it is assumed that the annual average mileage or hours accumulated by each model year of each class is also known.

For more information, see "Diesel Retrofits: Quantifying and Using Their Benefits in SIPs and Conformity - Guidance for State and Local Air and Transportation Agencies," http://www.epa.gov/otaq/stateresources/transconf/policy/420b14007.pdf.

It is important to only use verified emission reductions approved for the specific retrofit technology being considered. EPA and the California Air Resources Board (CARB) have retrofit technology verification programs that evaluate the performance of advanced emissions control technologies and engine rebuild kits. A list of EPA verified technologies is available at http://www.epa.gov/otaq/retrofit/index.htm and CARB's verification program can be found at http://www.arb.ca.gov/diesel/verdev/home/home.htm.

Sample Projects

Sample 1: Diesel Heavy Duty Truck Retrofit

This sample involves a trucking company retrofitting a heavy-duty diesel truck47.The following factors are drawn from the sample:

Step 1: Calculate retrofitted vehicle VMT.

= (Number to vehicles to be retrofit) x (average VMT per vehicle)
= (1) (100,000)
= 100,000

Step 2: Emissions reduced.

= [(Emission factor from old engines) x (percent emissions reduced)] x (retrofitted vehicle VMT)

Table 5-9. Total Emissions Reductions (tons/year) from Diesel Retrofit Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

0.009

0.004

0.138

NA

0.033

NA

NA

2010

0.005

0.006

0.080

NA

0.026

NA

NA

Emissions benefits are not calculated for 2020, due to lack of availability for emissions factors from EPA guidance and in consideration of the anticipated useful life of vehicle replaced.

Sample 2: PM-Focused Heavy Duty Truck Retrofit

The NMIM user guide scenario posits that a retrofit program is in place for calendar 2006 only and applies to 1990 model year trucks only.48 The inputs are as follows:

Table 5-10. Emissions Reductions (tons/year) from Diesel Retrofit Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

0.131

0.142

NA

NA

NA

NA

NA

2010

0.056

0.061

NA

NA

NA

NA

NA

2020

0.000

0.000

NA

NA

NA

NA

NA


Emissions benefits above vary from Sample 1 due to variances in the type of retrofit technology applied; Sample 2 utilizes technology aimed at reducing PM emissions.

25. Clean Diesel Fuels

Strategy Overview

Clean diesel fuels are a potential strategy to reduce emissions from both heavy-duty diesel vehicles and non-road diesel equipment. Clean diesel fuels include emulsified diesel, oxygenated diesel, biodiesel, or fuel borne catalysts. In addition, ultra-low sulfur diesel (ULSD) is increasingly available across the US and will continue to increase under the EPA's National Clean Diesel Campaign. Programs at the local level which increase the use of such fuels reduce emissions without changing driving behavior or the number of vehicles on the road or the use of diesel equipment.

Emissions Impacts

Emissions from diesel engines contribute to smog (ozone), particulate matter, and all air toxics. Cleaner fuels will tend to improve such emissions. However, the level of improvement will vary based on the type of fuel used. Some fuel types can also increase emissions of some pollutants, as shown below49.

Table 5-11. Clean Diesel - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH-3

decrease expected

decrease/no effect

decrease

decrease/increase

decrease

decrease/no effect

Letter N

Note: Impacts will vary based on type of clean diesel fuel applied.
(-) = Decrease expected, but not quantified in EPA guidance; N = No effect; not quantified in EPA guidance (will vary on type of clean diesel technology applied)

General Considerations

Factors affecting emissions reduction from cleaner diesel fuels include:

For a full life-cycle analysis, the emissions from fuel production and refining need to be added to tailpipe emissions from heavy-duty diesel trucks.

For EPA guidance, see "Guidance on Quantifying NOx Benefits for Cetane Improvement Programs for Use in SIPs and Transportation Conformity," http://www.epa.gov/otaq/guidance/420b04005.pdf.

Sample Projects

Sample 1: Cetane Enhancers

The addition of cetane enhancers to diesel fuel is one recognized retrofit technology used to reduce diesel engine emissions. Cetane enhancers are compounds added to diesel fuel oil to raise the fuel's measured cetane level. A city implements a demonstration program to raise the cetane level of fuel for calendar year 2006.50 Calculations are based on the following inputs:

Step 1: Calculate annual miles traveled.

= (Number of trucks in program) x (Average annual VMT)
= (50) x (15,000 miles)
= 750,000 miles

Step 2: Determine the NOx emission benefits using the EPA guidance51.

= k x 100% x [1- exp(- 0.015151 × AC + 0.000169 × AC2 + 0.000223 × AC × RC)]
= -1.5% (2006)
= -1.2% (2010)
= -0.8% (2020)

Step 3: Calculate emissions reduced.

= [(Emission factor from old engines) x (Percent emissions reduced)] x (VMT)

Table 5-12. Total Emissions Reduced (tons/year) from Clean Diesel Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH-3

2006

NA

NA

NA

0.08

NA

NA

NA

2010

NA

NA

NA

0.04

NA

NA

NA

2020

NA

NA

NA

<0.01

NA

NA

NA



Sample 2: Biodiesel

The addition of biodiesel to a base diesel fuel is a recognized clean diesel used to reduce diesel engine emissions. In this sample, a city implements a demonstration program to use diesel (non-ULSD) which has been modified to include 10 percent soybean biodiesel52.The specifics on the project are as follows:
10 medium heavy-duty trucks
Average activity of 15,000 miles each annually

Step 1: Replaced vehicle VMT.

= (Number of trucks in program) x (average annual VMT)
= (10) x (15,000 miles)
= 150,000

Step 2: Determine the specific emission benefits using EPA calculator.

= PM-10: -4%
= CO: -5%
= NOx: +1%
= VOC: -11%

Step 3: Emissions reduced.

= [(Emission factor from old engines) x (percent emissions reduced)] x (VMT)

Table 5-13. Total Emissions Reductions (tons/year) from Clean Diesel Example

Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH-3

2006

<0.01

<0.01

0.02

Increase
0.01

0.01

NA

NA

2010

<0.01

<0.01

0.01

Increase 0.01

0.01

NA

NA

2020

<0.01

<0.01

<0.01

Increase
<0.01

<0.01

NA

NA


Emissions benefits above vary from Sample 1 due to variances in the type of clean diesel technology applied.

26. Inspection & Maintenance Programs

Strategy Overview

A small percentage of vehicles, including older models and newer models with poorly maintained or malfunctioning emissions control equipment, emit a large share of motor vehicle pollution.; Consequently, programs designed to detect these "gross polluters" and require them to update their vehicle pollution controls can be very effective in reducing emissions. Examples of these programs include inspection and maintenance programs, on-board diagnostics, remote sensing of roadside pullovers, smoking vehicle programs which provide a toll free number for reporting high polluting vehicles, or frequent vehicle inspections. These programs reduce emissions by identifying and requiring improvements to vehicles with failing emissions control equipment and encouraging vehicle owners to monitor their vehicle's condition.

Emissions Impacts

A small percentage of vehicles, including older models and newer models with poorly maintained or malfunctioning emissions control equipment, emit a large share of motor vehicle pollution. Inspection and maintenance strategies that target these gross emitters can be very effective in reducing pollutants. VOCs and PM are most often reduced as a result of implementation.

Table 5-14. I&M Strategy - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

no change

no change

decrease

decrease

decrease

no change

no change


N = No change; not quantified in EPA guidance

General Considerations

Vehicle inspection and maintenance programs can be made more effective when implemented in conjunction with other strategies designed to accelerate retirement or create advanced technology purchasing incentives. Together, these strategies not only monitor the emissions of individual vehicles, but encourage owners to change their purchase behavior to further reduce emissions.

For EPA guidance, see 40 CFR Part 51, "Amendments to Vehicle Inspection Maintenance Program Requirements to Address the 8-hour National Ambient Air Quality Standard for Ozone; Notice of Proposed Rulemaking," 2005. Additional guidance documents can be found www.epa.gov/otaq/im.htm.

Sample Project

Vehicle Emissions Inspection Program

A statewide Vehicle Emissions Inspection Program (VEIP) aims to ensure that certain cars and trucks are properly maintained in accordance with manufacturer recommendations. The following I/M parameters were used as inputs in the MOBILE6 Model in order to estimate the emissions benefits accrued from the VEIP:

Emissions reductions were derived by taking the difference in MOBILE6.2 generated emissions between VEIP light-duty fleet participation and non-participation. Results are as follows:

Table 5-15. Total Emissions Reductions (tons/year) from Gross Polluters Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

0.00

0.00

45,483

1,778

2,908

0.00

0.00

2010

0.00

0.00

41,153

2,071

2,406

0.00

0.00

2020

0.00

0.00

35,378

2,532

1,883

0.00

0.00


43 Documented in "Guidance for Quantifying and Using Long Duration Truck Idling Emission Reductions in State Implementation Plans and transportation Conformity," by U.S.EPA, 2004.

44 Documented in "The Carl Moyer Memorial Air Quality Standards Attainment Program Guidelines," for the California Air Resources Board, 2003.

45 Documented in "The Carl Moyer Memorial Air Quality Standards Attainment Program Guidelines," for the California Air Resources Board, 2003.

46 A complete list of all EPA verified technologies and their expected emissions reductions for various pollutants are available at http://www.epa.gov/otaq/retrofit/index.htm.

47 Documented in "Diesel Retrofits: Quantifying and Using Their Benefits in SIPs and Conformity - Guidance for State and Local Air and Transportation, by U.S.EPA, 2006.

48 Documented in the National Inventory Model Run User's Guide, http://www.epa.gov/CAIR/pdfs/MobileNMIM_Documentation.pdf .

49 Biodiesel generally increases NOx emissions by a small amount (up to 10%); PuriNOX water emulsion can increase VOC by 30 to 120% and CO by up to 35%, according to EPA, http://www.epa.gov/otaq/retrofit/index.htm

50 http://www.epa.gov/cleandiesel/verification/techlist-cetane-enhancers.htm

51 http://www.epa.gov/otaq/guidance/420b04005.pdf.

52 http://www.epa.gov/cleandiesel/documents/biodiesel_calc.xls

Updated: 04/03/2014
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