1 

MEMORANDUM 

TO: Docket EPA-HQ-OAR-2011-0135 

FROM: James Warila, 

 Assessment and Standards Division, Office of Transportation and Air Quality

DATE: December 2011 

RE: Developing Emission Rates Representing the Effect of Proposed Tier-3 Standards 

on Gaseous Emissions from Gasoline-Powered Light-duty Vehicles (HC/CO/NOx) 

Gaseous emission rates in MOVES are stored in a database table (EmissionRateByAge) that 

expresses emission rates as mass per time, distinguished by emission process (start and running), 

fuel type (gas and diesel), vehicle regulatory class (LDV, LDT, Light HD, etc.), model year, 

age, and operating mode (power/speed for running, vehicle soak time for start). Developing 

rates to reflect Tier 3 controls required accounting for expected changes in each of these 

dimensions. 

Developing rates to represent emissions for Tier-3 vehicles follows same procedures used to 

develop rates used in the default database, as described in the documentation for development of 

light-duty exhaust emission rates for MOVES2010i

. However, specific modifications were 

made to represent the introduction of Tier-3 standards, as described below. Where no 

modifications to methods were made, we will refer the reader to the appropriate section of the 

MOVES2010 report. In particular, see Section 1.3.4. 

The process involves six steps, listed below. As described in the report, the first four steps in 

this process are applied to calculate the meanBaseRateIM1 for the 0-3 year ageGroup (with 

deterioration to be applied in Step 5). The rates are estimated by Tier, model year and regulatory 

class. 1. Average FTP results by standard level and vehicle class. As in the default database, we 

made use of data measured on the FTP cycle in the course of the In-use Verification Program 

(IUVP). 

2. Develop phase-in assumptions for MY 2017 – 2031, by standard level, vehicle class and 

model year. 

3. Merge FTP results and Phase-in assumptions. For running emissions, calculate weighted 

ratios of emissions in each model year relative to those for cars (LDV) in MY2000, which 

represent Tier-1 LDV. 

 1

 The field “meanBaseRateIM” in the emissionRateByAge table represents mean rates for vehicles subject to 

requirements of the Phoenix Inspection-and-Maintenance Program. In the technical report, this field is referred to as 

the “I/M Reference rate.” However, this use of the term should not be confused with the “Reference Case” in the 

Rulemaking. 
2 

4. Estimate Emissions by Operating Mode. Then calculate emissions by operating mode in 

each model year by multiplying the MY2000 emission rates by the weighted ratio for each model 

year. We assume that the emissions control at high power (outside ranges of speed and 

acceleration covered by Bag 2 of the FTP) would not be as effective as at lower power (within 

the range of speed and acceleration covered by Bag 2). 

5. Apply Deterioration to estimate emissions for three additional age Groups (4-5, 6-7 and 8-

9). We assume that NLEV and Tier-2 vehicles will deteriorate similarly to Tier-1 vehicles, when 

viewed in logarithmic terms. We therefore apply ln-linear deterioration to the rates developed in 

steps 1-4. For the remaining three age groups, emissions are assumed to stabilize as described in 

the MOVES2010 report. 

6. Estimate non-I/M reference rates. The rates in steps 1-6 represent I/M references. 

Corresponding non-I/M references are calculated by applying the ratios applied to the Tier-1 and 

pre-Tier-1 rates. 

We followed these steps, with specific modifications to represent Tier 3 rates. In step 1, we 

developed estimates of FTP results under Tier 3, including composite results, “cold-start” 

emissions” (Bag1-Bag3) and “hot-running” emissions (Bag 2 FTP and US06). For step 2, we 

developed phase-in assumptions representing the introduction of Tier-3 standards. In Step 5 we 

modified deterioration to represent a useful life of 150,000 miles, as opposed to the useful life of 

120K mi, assumed for Tier-2 and NLEV vehicles. Each of these steps and modifications is 

described in greater detail in the sub-sections below. 

1.1 Averaging FTP Results (Step 1) (Standard) 

Modeling to project emissions for Tier-3 vehicles is driven by the NMOG+NOx standard, set 

at 30 mg/mi. However, because MOVES projects NOx and THC emissions separately, we 

apportioned the aggregate standard into NMOG and NOx components, which we will refer to as 

the “effective standards” for each pollutant. For purposes of apportionment, we assumed that 

NMOG control would pose a greater technical challenge than NOx control. Accordingly, we 

assumed “effective standards” for NMOG and NOx of 20 mg/mi and 10 mg/mi, respectively. To 

implement this assumption, we further assumed that for NOx, vehicles would be effectively 

brought into Bin 2, and that for NMOG, vehicles would be brought to a level between Bin 2 and 

Bin 3, but closer to Bin 2. 

In addition, MOVES models start and running processes separately. It is therefore necessary 

to translate the composite standard into start and running components. One component 

represents a “cold start” on the FTP cycle, represented as “Bag1 – Bag3” emissions. A second 

component represents “hot-running” emissions, represented by the hot-running phase of the FTP 

(Bag 2). A third component represents emissions on the US06 cycle, representing emissions at 

high speed and power. 

Estimated FTP and US06 emissions levels for hydrocarbons (NMOG and NMHC) are shown 

in Table 1, for several Tier-2 Bins and for Tier 3. Values for all standards except Tier 3 are 
3 

identical to those used to develop rates in the default database. The values for Tier 3 are 

calculated as a weighted average of those for Bins 2 and 3, using Equation 1. 

T3  0.775B2  0.225B3 Equation 1 

 

Table 1. Hydrocarbons (HC): Useful-Life FTP Standards and Associated Cold-Start and 

Hot-Running Results on the FTP and US06 Cycles. Values for the FTP and US06 represent 

NMOG and NMHC, respectively. 

Bin Useful-life Standard 

(mg/mi) 

FTP Composite1

(mg/mi) 

FTP Cold Start1

(mg) 

FTP hot Running1 

(Bag 2) 

(mg/mi) 

US062 

(mg/mi)

8 125 41.3 591 3.56 35.8 

5 90 35.5 534 2.63 35.8 

4 70 24.8 383 2.28 35.8 

3 55 21.5 329 1.74 35.8 

2 10 5.6 87 0.42 2.60 

 

Tier 33 20 9.2 142 0.7 10.0 

1 Values represent “non-methane organic gases” (NMOG). 

2 Values represent “non-methane hydrocarbons” (NMHC). 

3 Values for Tier 3 calculated using Equation 1.

Under a general assumption that CO standards are not forcing, but that CO emissions tend to 

track NMOG emissions, corresponding values for CO were calculated in the same manner, and 

are presented in Table 2. 

Table 2. CO: Useful-Life FTP Standards and Associated Cold-Start and Hot-Running 

Results on the FTP and US06 Cycles. 

Bin Useful-lifeStandard 

(mg/mi) 

FTP Composite 

(mg/mi) 

Cold Start 

(mg) 

FTP hot Running 

(Bag 2) 

(mg/mi) 

US06 

(mg/mi)

8 4,200 861 6,680 451 2,895 

5 4,200 606 5,510 238 2,895 

4 4,200 537 5,500 201 2,895 

3 2,100 463 3,470 119 2,895 

2 2,100 235 1,620 70 948 

 

Tier 31 2,100 286 2,040 81 1,390 

1 Values for Tier 3 calculated using Equation 1.
4 

Corresponding results for NOx are presented in Table 3. In contrast to HC and CO, the values 

for Bin 2 were adopted for Tier 3, as the FTP composite of 5.5 mg/mi suggests that Bin-2 

vehicles can meet the “effective standard” of 10 mg/mi with a reasonable compliance margin. 

Table 3. NOx: Useful-Life FTP Standards and Associated Cold-Start and Hot-Running 

Results on the FTP and US06 Cycles. 

Bin Useful-lifeStandard 

(mg/mi) 

FTP Composite 

(mg/mi) 

Cold Start 

(mg) 

FTP hot Running 

(Bag 2) 

(mg/mi) 

US06 

(mg/mi)

8 200 64.2 418 35.1 61.3 

5 70 21.2 165 8.2 45.9 

4 40 8.7 90 4.7 30.6 

3 30 5.7 71 3.8 30.6 

2 20 5.5 67 0.4 18.4 

 

Tier 31 10 5.5 67 0.4 18.4 

 
5 

1.2 Develop Phase-In Assumptions (Step 2) 

We designed phase-in assumptions so as to project compliance with the Tier-3 fleet average 

NMOG+NOx requirements. The requirements are shown in Table 4 for cars and trucks. The 

phase-in begins in model year 2017 and ends in model year 2025. 

Table 4. Target NMOG+NOx Fleet Average Requirements for the Federal Test Procedure. 

Model year FTP Composite, NMOG+NOx (g/mi) 

 LDV/T1 LDT21

2017 0.086 0.101 

2018 0.079 0.092 

2019 0.072 0.083 

2020 0.065 0.074 

2021 0.058 0.065 

2022 0.051 0.056 

2023 0.044 0.047 

2024 0.038 0.038 

2025 0.030 0.030 

1 Throughout, these results applied to Federal truck classes 

LDT2, LDT3 and LDT4.

These results are also pictured in Figure 1. Note the sharp drop in emissions at the outset of 

the Tier-3 phase-in, also that the truck requirements (LDT2,3,4) are slightly higher than those for 

the lighter vehicles (LDV-T1). After 2017, the reduction in the fleet average is linear, and at the 

completion of the phase-in, fleet averages for cars and trucks no longer differ. 
6 

Figure 1. NMOG+NOx FTP Fleet Average Requirements during Phase-In of the Tier-3 

Exhaust Emissions Standards for Light-Duty Vehicles. 

In development of MOVES rates we translated the fleet requirements so as to develop phasein assumptions representing the introduction of Tier-3 vehicles and concurrent replacement of 

Tier-2 vehicles. For purposes of model input development, we project phase-ins for four 

categories of Federally-certified vehicles, LDV-T1, LDT2, LDT3 and LDT4. 

These phase-in fractions give emission rates that reproduce the fleet requirements when FTP 

composites are calculated by combining start and running rates. To represent the fleet 

requirements, the phase-in assumptions are “linear” and “proportional.” 

By “linear” we mean that the fractions of Tier-2 vehicles, whether taken all together, by 

vehicle class or by Bin, decline linearly during the phase-in period. We represent them this way 

because the fleet requirements also decline linearly. 

By “proportional,” we mean that during the phase-in, the various bins within a vehicle class 

maintain the same relative proportions as in MY 2016, at the outset of the phase-in. For 

example, in 2016, we assume that 89% and 3.5% of LDV-T1 vehicles are in Bins 5 and 3, 

respectively. This difference implies that the fleet comprises 25.43 times as manyBin-5 vehicles 

as Bin-3 vehicles (0.89/0.035). This ratio holds in any given model year during the phase-in. In 

MY 2023, the remaining fractions of Bin 5 and Bin 3 are 10.18% and 0.40%, which give the 

same ratio as in MY 2016. The same proportional approach was applied to LDT2, LDT3 and 

LDT4. Phase-in assumptions, expressed as the relative composition of Bins within each vehicle 

class, are presented in Figure 2 through Figure 5. 

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0.180

201520162017201820192020202120222023202420252026

FTP Composite Standard (g/mi)

Model Year

LDV/LDT1

LDT234
7 

Figure 2. Phase-in Assumptions, by Standard and Bin, for LDV-T1 Vehicles. 

Figure 3. Phase-in Assumptions, by Standard and Bin, for LDT2 Vehicles. 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2016201720182019202020212022202320242025

Relative Composition(%)

Model Year

T3

Bin 2

Bin 3

Bin 4

Bin 5

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2016201720182019202020212022202320242025

Relative Composition(%)

Model Year

T3

Bin 3

Bin 4

Bin 5
8 

Figure 4. Phase-in Assumptions, by Standard and Bin, for LDT3 Vehicles. 

Figure 5. Phase-in Assumptions, by Standard and Bin, for LDT4 Vehicles. 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2016201720182019202020212022202320242025

Relative Composition (%)

Model Year

T3

Bin 4

Bin 5

Bin 8

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2016201720182019202020212022202320242025

Relative Composition(%)

Model Year

T3

Bin 5

Bin 8
9 

1.3 Merge Cycle Results and Phase-In Assumptions (Step 3) 

The goal of this step is to calculate weighted averages of the FTP (cold-start and hot-running) 

results for all standards in each model year, with the emissions results weighted by applicable 

phase-in fractions. We do this step for each vehicle class separately, then weight the four truck 

classes together using a set of fractions derived from the weighted sales estimates. 

Figure 6 shows an example of the phase-in calculation for NOx from cars between model 

years 2016 and 2025. The figure shows cold-start and hot-running FTP values for Tier-1, Tier-2 

and Tier-3 standards, as well as the phase-in fractions for each standard in each model year. 

Start and running emissions in each model year are simply calculated as weighted averages of 

the emissions estimates and the phase-in fractions. The resulting weighted start estimates are 

used directly to represent cold-start emissions for young vehicles in each model year (ages 0-3). 

For running emissions, however, the averages are not used directly; rather, each is expressed as a 

ratio to the corresponding Tier-1 value. 

Table 5 shows weighted average values for model-years 2016-2025 for simulated FTP 

composites, cold-start and hot-running emissions. The start values, expressed as the cold-start 

mass increment (g), are used directly in the MOVES emission rate table to represent cold-start 

emissions (operating mode 108). The composites and running emissions, expressed as rates 

(g/mi), are presented for comparison. For running emissions, however, the averages shown in 

the table are not used directly; rather, each is expressed as a ratio to the corresponding Tier-1 

value, as shown in Figure 7 to Figure 9 below. 

Figure 6. Example of Phase-In Calculation, for NOx from LDV-T1, for MY 2016-2025. 

 Standard Cold 

Start

Hot 

Running

(mg) (mg/mi) 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025

Tier 1 Tier 1 888.00 127.00 0 0 0 0 0 0 0 0 0 0

Bin 8 417.87 35.07 0 0 0 0 0 0 0 0 0 0

Bin 5 165.42 8.21 0.890 0.407 0.356 0.305 0.254 0.204 0.153 0.102 0.058 0

Tier 2 Bin 4 89.72 4.69 0.060 0.027 0.024 0.021 0.017 0.014 0.010 0.007 0.004 0

Bin 3 70.89 3.78 0.010 0.016 0.014 0.012 0.010 0.008 0.006 0.004 0.002 0

Bin 2 67.18 0.38 0.015 0.007 0.006 0.005 0.004 0.003 0.003 0.002 0.001 0

Tier 3 Tier 3 67.18 0.38 0.000 0.543 0.600 0.657 0.714 0.771 0.829 0.886 0.935 1.000

Cold Start (mg) 154.32 107.85 102.76 97.69 92.60 87.52 82.43 77.35 72.99 67.18

Hot Running (mg/mi) 7.64 3.74 3.32 2.90 2.48 2.06 1.64 1.22 0.86 0.38

RATIO to Tier 1 0.0601 0.0295 0.0262 0.0228 0.0195 0.0162 0.0129 0.00961 0.00677 0.00299

Phase-In by Model Year
10 

Table 5. Weighted Average FTP Values Projected for Trucks and Cars for MY 2017-2025. 

regClass MY CO HC NOx 

 Composite 

(mg/mi) 

Start 

(mg) 

Running 

(mg/mi) 

Composite 

(mg/mi) 

Start 

(mg) 

Running 

(mg/mi) 

Composite 

(mg/mi) 

Start 

(mg) 

Running 

(mg/mi) 

Ref.1 1,620 11,400 805 126 1,530 57.1 209 888 12.7 

Trucks 2017 455 3,855 166 22.4 368 2.97 14.2 121 5.04 

2018 434 3,625 155 20.7 341 2.76 13.1 114 4.45 

2019 412 3,395 144 19.0 314 2.54 12.0 108 3.86 

2020 391 3,164 134 17.3 287 2.32 10.9 101 3.27 

2021 369 2,934 123 15.7 260 2.10 9.82 93.9 2.68 

2022 348 2,704 112 14.0 233 1.88 8.72 87.0 2.09 

2023 327 2,474 101 12.3 206 1.66 7.62 80.2 1.50 

2024 305 2,246 91 10.7 179 1.45 6.53 73.4 0.914 

2025 286 2,037 81 9.2 154 1.25 5.54 67.2 0.380 

Cars 2017 426 3,566 149 20.5 339 2.70 12.0 108 3.74 

2018 408 3,375 140 19.1 316 2.52 11.2 103 3.32 

2019 3991 3,184 132 17.7 293 2.34 10.4 97.7 2.90 

2020 373 2,993 123 16.3 270 2.16 9.60 92.6 5.48 

2021 356 2,802 115 14.8 247 1.97 8.77 87.5 2.06 

2022 338 2,610 106 13.4 224 1.79 7.96 82.4 1.64 

2023 321 2,419 98 12.0 201 1.61 7.16 77.4 1.22 

2024 306 2,255 91 10.8 181 1.46 6.46 73.0 0.860 

2025 286 2,037 81 9.2 154 1.25 5.54 67.2 0.380 1

 The reference level represents Tier-1 LDV-T1. 

 
11 

Figure 7. Weighted Ratios for Composite, Start and Running CO Emissions, for (a) 

Trucks and (b) Cars. 

0.206 0.193 0.179 0.166 0.153 0.139 0.126 0.113 0.101

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

201720182019202020212022202320242025

Weighted Ratio

Model Year

Composite

Cold Start

Hot Running

0.185 0.174 0.164 0.153 0.143 0.132 0.122 0.113 0.101

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

201720182019202020212022202320242025

Weighted Ratio

Model Year

Composite

Cold Start

Hot Running

(a) Trucks

(b) Cars
12 

Figure 8. Weighted Ratios for Composite, Start and Running THC Emissions, for (a) 

Trucks and (b) Cars. 

0.00

0.052 0.048 0.044 0.041 0.037 0.033 0.029 0.025 0.022

0.05

0.10

0.15

0.20

0.25

0.30

201720182019202020212022202320242025

Weighted Ratio

Model Year

Composite

Cold Start

Hot Running

0.047 0.044 0.041 0.038 0.035 0.031 0.028 0.026 0.00 0.022

0.05

0.10

0.15

0.20

0.25

201720182019202020212022202320242025

Weighted Ratio

Model Year

Composite

Cold Start

Hot Running

(a) Trucks

(b) Cars
13 

Figure 9. Weighted Ratios for Composite, Start and Running NOx Emissions, for (a) 

Trucks and (b) Cars. 

0.040 0.035 0.030 0.026 0.021 0.016 0.012 0.007 0.003

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

201720182019202020212022202320242025

Weighted Ratio

Model Year

Composite

Start

Hot Running

(a) Trucks

0.029 0.026 0.023 0.020 0.016 0.013 0.010 0.007 0.003

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

201720182019202020212022202320242025

Weighted Ratio

Model Year

Composite

Cold Start

Hot Running

(b) Cars
14 

1.4 Estimating Emissions by Operating Mode (Step 4) 

To project emissions for Tier-2 and Tier-3 vehicles, we divided the operating modes for 

running exhaust into two groups. These groups represent the ranges of speed and power covered 

by the hot-running phase (Bag 2) of the FTP standards (< ~20 kW/Mg), and the ranges covered 

by the SFTP standards (primarily the US06 cycle). For convenience, we refer to these two 

regions as “the hot-running FTP region” and “US06 region,” respectively (See Figure 10). Data 

measured on the SC03 cycle did not play a role in emission rate development. 

 To estimate emissions by operating mode, the approach was to multiply the emission rates 

for MY 2000, representing Tier 1, by a specific ratio for each model year from 2016 to 2025, to 

represent emissions for that model year. For the FTP operating modes, we applied the ratios 

shown in Figure 7 to Figure 9 above. 

To estimate rates for the US06 modes, we followed a procedure similar to that for the “FTP” 

modes, but using the “US06” columns in Table 1 through Table 3. For HC and CO, we used 

Equation 1, as before. For NOx, we applied the Bin-2 values. Figure 11 through Figure 13 show 

fractional reductions in the US06 rates along with similar reductions in hot-running operation, 

relative to levels for MY 2000 cars (Tier-1 levels). Note that the trends for “hot-running” are 

identical to those in Figure 7 through Figure 9. 

Figure 14 and Figure 15 show application of the ratios to the FTP and US06 operating modes 

in model years 2010, 2017, and 2025, representing fully phased-in Tier-2 standards, an interim 

year during the Tier-3 phase-in, and the fully phased-in Tier-3 standards, respectively. Rates for 

all three years are calculated with respect to rates for cars in model-year 2000, using reduction 

ratios shown above in Figure 11 through Figure 13, applied to rates in all operating modes for 

running operation. In these figures, the results are presented on both linear and logarithmic 

scales. The linear plots display the differences in the high-power modes, but obscure those in the 

low-power modes. The logarithmic plots supplement the linear plots by making visible the 

relatively small differences in the lower power modes. They also illustrate the varying degrees of 

control between the “hot-running FTP” (< 20 kW/Mg) and the “US06” (> 20 kW/Mg) modes. In 

addition, the logarithmic plots include the level for MY2000, which represents Tier-1 standards. 

Thus, these plots display the degree of running-emissions reduction between Tier1 and Tier 2 

(MY2000: MY2010), and between Tier 2 and Tier 3 (MY2010: MY2025), across the full range 

of vehicle-specific power. Note that for simplicity, these figures represent rates for operating 

modes 21-30, covering a wide range of power for vehicles operating at speeds between 25 and 

50 mph. 

 
15 

Figure 10. Operating modes for running Exhaust Emissions, divided broadly into “hotrunning FTP” and “US06” regions. 

 Vehicle-Specific Power (kW/tonne)

The “hot-running FTP Region”

Low to Moderate 

Power

(also includes braking (0)

and idle (1)

The “US06 Region”

High Power 
16 

 

Figure 11. CO: Weighted Ratios for Cars, for hot-running emissions, representing the 

“hot-running FTP Region” (FTP) and the “US06 Region” (US06), for (a) Trucks and (b) 

Cars. 

0.206 0.193 0.179 0.166 0.153 0.139 0.126 0.113 0.101

0.488

0.459

0.431

0.402

0.374

0.346

0.317

0.289

0.263

0.00

0.10

0.20

0.30

0.40

0.50

0.60

201720182019202020212022202320242025

Weighted Ratio

Model Year

Hot Running

US06

0.185 0.174 0.164 0.153 0.143 0.132 0.122 0.113 0.101

0.392 0.376 0.360 0.344 0.328 0.311 0.295 0.282

0.263

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

201720182019202020212022202320242025

Weighted Ratio

Model Year

Hot Running

US06

(a) Trucks

(b) Cars
17 

 

Figure 12. THC: Weighted Ratios for Cars, for hot-running emissions, representing the 

“hot-running FTP Region” (FTP) and the “US06 Region” (US06), for (a) Trucks and (b) 

Cars. 

0.052 0.048 0.044 0.041 0.037 0.033 0.029 0.025 0.022

0.327

0.298

0.269

0.240

0.211

0.182

0.153

0.124

0.098

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

201720182019202020212022202320242025

Weighted Ratio

Model Year

Hot Running

US06

0.047 0.044 0.041 0.038 0.035 0.031 0.028 0.026 0.022

0.211

0.197

0.183

0.169

0.155

0.140

0.126

0.114

0.098

0.00

0.05

0.10

0.15

0.20

0.25

201720182019202020212022202320242025

Weighted Ratio

Model Year

Hot Running

US06

(a) Trucks

(b) Cars
18 

 

Figure 13. NOx: Weighted Ratios for Cars, for hot-running emissions, representing the 

“hot-running FTP Region” (FTP) and the “US06 Region” (US06), for (a) Trucks and (b) 

Cars. 

0.040 0.035 0.030 0.026 0.021 0.016 0.012 0.007 0.003

0.168

0.154

0.140

0.127

0.113

0.099

0.086

0.072

0.060

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

201720182019202020212022202320242025

Weighted Ratio

Model Year

Hot Running FTP

US06

0.029 0.026 0.023 0.020 0.016 0.013 0.010 0.007 0.003

0.098

0.094

0.089

0.084

0.079

0.074

0.070 0.065

0.060

0.00

0.02

0.04

0.06

0.08

0.10

0.12

201720182019202020212022202320242025

Weighted Ratio

Model Year

Hot Running FTP

US06

(b) Cars

(a) Trucks
19 

 

Figure 14. Projected Emission Rates for Cars in Operating modes 21-30, vs. VSP, in 

ageGroup 0-3 years, for three model years, for (a) CO, (b) THC and (c) NOx (LINEAR 

SCALE). 

0

100

200

300

400

500

600

700

800

900

1,000

-5 0 5 10 15 20 25 30 35 40

Emission Rate (g/hr)

Vehicle Specific Power (kW/Mg)

2010

2017

2025

0

1

2

3

4

5

6

7

-5 0 5 10 15 20 25 30 35 40

Emission Rate (g/hr)

Vehicle Specific Power (kW/Mg)

2010

2017

2025

0

2

4

6

8

10

12

14

16

18

-5 0 5 10 15 20 25 30 35 40

Emission Rate (g/hr)

Vehicle Specific Power (kW/Mg)

2010

2017

2025

(b) THC

(c) NOx

(a) CO
20 

Figure 15. Projected Emission Rates for Cars in Operating modes 21-30, vs. VSP, in 

ageGroup 0-3 years, for Four Model Years, for (a) CO, (b) THC and (c) NOx 

(LOGARITHMIC SCALE). 

0.01

0.10

1.00

10.00

100.00

-10 0 10 20 30 40

Emission Rate (g/hr)

Vehicle Specific Power (kW/Mg)

2000

2010

2017

2025

0.001

0.010

0.100

1.000

10.000

100.000

1,000.000

-5 0 5 10 15 20 25 30 35 40

Emission Rate (g/hr)

Vehicle Specific Power (kW/Mg)

2000

2010

2017

2025

(c) NOx

1

10

100

1,000

10,000

-10 0 10 20 30 40

Emission Rate (g/hr)

Vehicle Specific Power (kW/Mg)

2000

2010

2017

2025

(a) CO

(b) THC
21 

1.5 Apply Deterioration (Step 5) 

Based on review and analysis data from the Phoenix Inspection-and-Maintenance Program, 

we assume that deterioration for different technologies is best represented by a multiplicative 

model, in which different technologies, represented by successive model-year groups, show 

similar deterioration in relative terms but markedly different deterioration in absolute terms. We 

implemented this approach by translating emissions for the 0-3 age Group, as calculated above, 

into their respective logarithmic means and applying uniform logarithmic age trends to all 

model-year groups. We derived logarithmic deterioration slopes for Tier-1 vehicles (MY 1996-

98) and applied them to Tier-2 vehicles. In this process we applied the same logarithmic slope to 

each operating mode, which is an extension of the multiplicative deterioration assumption. 

For Tier-3 vehicles, the deterioration assumptions were modified to represent an extension of 

the full useful life (FUL), which is increased from 120,000 mi to 150,000 mi. The extension of 

the useful life, which assumes improved durability, was expressed through a reduction in 

deterioration. 

To represent improved durability, differential reductions were applied to logarithmic 

deterioration for THC and NOx. These reductions were applied such that when FTP composites 

were reconstructed from the resulting emission start and running emission rates, the reduction in 

deterioration was proportional to the increase in the useful life. The reductions achieving this 

goal were 27% and 14% for THC and NOx, respectively. 

Note that in the reconstruction of FTP composites for NMOG+NOx, values for NMOG were 

estimated from those for THC. In this step the fraction of THC representing NMOG for start 

emissions was higher than that for running emissions2. In addition, start deterioration for THC 

(and NMOG) followed lower relative rates than running deterioration, whereas start and running 

NOx emissions deteriorate at the same relative rates (sec. 1.4.3). 

Results are shown in Figure 16. In MOVES, deterioration is expressed in terms of vehicle 

age, rather than mileage. However, assuming typical mileage accumulation of 10,000 to 15,000 

miles per year, we assume that vehicles reach the end of their useful lives between 10 and 15 

years of age, or between the 8-9 year and the 10-14 year ageGroups. Accordingly, deterioration 

for THC and NOx was modified so that the value of NMOG+NOx reached in the 8-9 year 

ageGroup under a 120K FUL assumption, would be reached in the 10-14 year ageGroup under a 

150K FUL assumption. Note that in that plot the value for each ageGroup is assigned to the 

midpoint of the group, i.e., the value for the 8-9 year ageGroup is shown at 9 years, and that for 

the 10-14 year ageGroup is shown at 12.5 years. 

We do not assume that emission rates for young vehicles, i.e., in the 0-3 year ageGroup, 

would differ under either assumption, as vehicles meet the same levels at certification. Thus, the 

deterioration trends for the two cases diverge as the vehicles age. We assume that the most rapid 

changes in fleet means occur during the first 10 years of life, or between the 0-3 year ageGroup 

 2

 For start emissions, NMOG = 0.89×THC, and for running emissions NMOG = 0.57×THC. 
22 

and the 8-9 year ageGroup. After that point, we assume that the rate of change declines as the 

fleet means tend to stabilize (especially in I/M areas, which are represented in the plot). The 

ratio between values for the 150K FUL and 120K FUL starts at 1.0 and declines, stabilizing at a 

value of 0.85 in the 8-9 year ageGroup, and remaining constant thereafter. Accordingly, we 

assume that the around the end of the useful life, mean FTP emissions for vehicles certified at 

150K mi would be approximately 85% of those certified at 120K mi. 

Figure 16. Simulated FTP composites for NMOG+NOx, calculated from MOVES start and 

running rates, under 120K and 150K FUL assumptions. 

1.5.1 Recalculate the logarithmic mean 

Starting with the values of the arithmetic mean (xa) calculated in steps 1-4, we calculate a 

logarithmic mean (xl), as shown in Equation 2. 

2

ln

2

l

l a x x

   Equation 2 

The logarithmic variance expresses the degree of skewness in the distribution of emissions, as 

the difference between the arithmetic mean and the geometric mean, of which the arithmetic 

mean is always larger. We assume that this term changes over time, reflecting differing degrees 

in the relative skewness of the underlying emissions distributions as vehicles age (Table 7 

below). The values of the logarithmic variance σl

2

are intended to represent values for young 

vehicles, as the estimates for xa represent the 0-3 year age Group. The values of σl

2

used for this 
23 

step were 1.30, 0.95 and 1.60 for CO, THC and NOx, respectively, as used in developing default 

rates for MOVES2010. 

1.5.2 Apply a logarithmic Age slope 

After estimating logarithmic means for the 0-3 age class (xl,0-3), we estimate additional 

logarithmic means for successive age classes (xl,age), by applying a linear slope in ln-space (ml). 

(age -1.5) l,age l,0 3 ml x  x   Equation 3 

The values of the logarithmic slope are adapted from values developed for the 1996-98 model 

–year group. The values applied to Tier-2 and Tier-3 vehicles are shown in Table 6. The 

reduced slopes for Tier-3 were calculated by reducing the Tier-2 values by 27% for HC and CO 

and by 14% for NOx. When calculating the age inputs for this equation, we subtracted 1.5 years 

to shift the intercept to the midpoint of the 0-3 year age Group, as shown in Equation 3. 

Table 6. Values of the logarithmic deterioration slope applied to running-exhaust emission 

rates for MY following 2000. 

Pollutant Operating-Mode Group Logarithmic Slope (ml) 

 Tier 2 Tier 3 

CO “hot-running FTP”1 0.13 0.0949 

“US06”2 0.06 0.0438 

THC “hot-running FTP” 0.09 0.0657 

“US06” 0.09 0.0657 

NOx “hot-running FTP” 0.15 0.129 

“US06” 0.15 0.129 

1

 Includes opModeID = 0,1, 11-16, 21-25, 27, 33,35,37. 

2

 Includes opModeID = 28,29,30, 38,39,40.

1.5.3 Apply the reverse transformation 

After the previous step, the values of xl,age were reverse-transformed, as in Equation 4, where 

Y is the emission rate in “linear space,” (g/hr) and sl

2

 is the logarithmic variance. The values of 

the logarithmic variance used for this step were adapted from the Phoenix I/M results and are 
24 

intended to represent emissions distributions for “real-world” vehicle populations, meaning that 

the values are higher than those listed above and may vary with age. Values of logarithmic 

variances for all three pollutants are shown in Table 7. 

2 ln ,age 0.5 e e l xl s Y  Equation 4 

 Table 7. Values of Logarithmic Variance Used to Calculate Emissions Deterioration by 

Reverse Transformation of Logarithmic Means. 

Age Group Pollutant 

 CO THC NOx

0-3 years 1.30 0.95 1.60 

4-5 2.05 1.50 1.60 

6-7 2.00 1.70 1.40 

8-9 1.80 1.90 1.40 

Note that no values are presented in the table for the 10-14, 15-19 and 20+ year age Groups. 

This omission is intentional, in that we did not want to extrapolate the deterioration trend beyond 

the 8-9 year age Group. Extrapolation beyond this point is incorrect, as we know that emissions 

tend to stabilize beyond this age, while the ln-linear emissions model would project an 

increasingly steep and unrealistic exponential emissions trend. For the 10-14, 15-19 and 20+ age 

Groups, the “stabilization of emissions with age” was estimated as for MOVES2010 (section 

1.3.3.7). 

Note that the “stabilization” is applied independently to the deterioration trends for Tier-2 and 

Tier-3 vehicles. The trends in Figure 16 show that the relative differences or ratios between the 

8-9 year values and those for the three successive ageGroups are the same for both Tier-2 and 

Tier-3 vehicles. 

1.6 Estimate non-I/M References (Step 6) 

Completion of the preceding steps provided a set of rates representing I/M reference rates for 

MY 2016-2025. As a final step, we estimated non-I/M reference rates by applying the same 

ratios applied to the I/M references for default rates in MOVES2010 (section 1.3.3.6). 

1.7 Start Emissions 

The values for “FTP Cold-start” shown in Table 5 above were used to represent cold-start 

emissions (opModeID=108). Rates for “warm” or “hot” starts following a range of soak periods 
25 

were estimated as in MOVES2010 (see 1.4.2). Deterioration was applied to start emissions, 

relative to that for running emissions, also as in MOVES2010 (see 1.4.3). 

1.8 Deterioration and the Benefits of Warranty Extension 

EPA is proposing to provide manufacturers an NMOG+NOx credit of 5 mg/mi, which can be 

applied to certification emissions levels for specific test groups in the calculation of fleet 

averages. The credit can be applied a test group if the manufacturer assumes the liability of 

warranting their emissions-related components and systems for the entire useful life of 150,000 

miles. This warranty period is considerably longer and the proposed warranty more robust than 

the primary EPA emissions warranty, which expires at 80,000 miles of operation and applies to 

fewer components and systems. 

To estimate the size of the anticipated benefit to the environment due to extending the 

warranty for emissions controls we can reexamine the fleet average trends presented in Figure 16 

above, although for purposes of this discussion we will assume that they apply to a single test 

group rather than to the fleet as a whole. In considering the warranty, we compared the values 

of the mean at the end of the primary warranty (80,000 miles) and at the end of the useful life 

(150,000 miles). We assume that vehicles in the test group tend to reach 80,000 miles at about 

10 years of age and 150,000 miles at about 13 years of age, and we further assume that the 

continued operation of the warranty would neutralize any additional increase in the test group 

mean. i.e., the emissions trend would be level after 10 years of age. On this basis, we estimate 

that the difference between the mean at 80,000 miles (the maximum with a full-life warranty) 

and the mean at 150,000 miles (assuming emissions continued to deteriorate without the 

warranty) is about 6 mg/mi. Thus, the emissions benefit attributable to the extended 150,000-

mile warranty is projected to exceed the proposed 5 mg/mi credit for NMOG+NOx. 

 

i

 US. EPA. Office of Transportation and Air Quality. Development of Emission Rates for Light-Duty Vehicles in the 

Motor Vehicle Emissions Simulator (MOVES2010): Final Report. (EPA-420-R-11-011) Assessment and Standards 

Division, Ann Arbor, MI. August, 2011. http://www.epa.gov/otaq/models/moves/documents/420r11011.pdf.