Supplement to the 

Redesignation Demonstration 

and 

Maintenance Plan 

for 

The Rocky Mount, North Carolina 

8-Hour Ozone Nonattainment Area 

Prepared by 

North Carolina Department of Environment and Natural Resources 

Division of Air Quality 

June 19, 2006 

Revised February 7, 2011 
(This page intentionally left blank)
Rocky Mount, NC 1 

Supplement to the Redesignation Demonstration and Maintenance Plan February 7, 2011 

INTRODUCTION 

This document is intended to supplement the Redesignation Demonstration and Maintenance 

Plan for the Rocky Mount, North Carolina 8-Hour Ozone Nonattainment Area that was 

submitted to the United States Environmental Protection Agency on June 19, 2006. This 

document revises the motor vehicle emission budgets to account for new emission models, 

vehicle miles traveled projection models and other emission model input data. 

REVISED SECTIONS 

Attached are the revised sections to the Redesignation Demonstration and Maintenance Plan for 

the Rocky Mount, North Carolina 8-Hour Ozone Nonattainment Area. To appropriately revise 

the original package, replace the pages as outlined below: 

Narrative Replacements 

Replace June 19, 2006 pages 4-2 through 4-4 with the attached February 7, 2011 pages 4-2 

through 4-4. (Note that June 19, 2006 page 4-1 has been included for ease of substitution.) 

Appendix B Replacements 

Add February 7, 2011 Appendix B pages 14 through 18 to the end of June 19, 2006 Appendix B. 

Appendix C Replacements 

Replace June 19, 2006 Appendix C.3 pages 4-28 through 4-30 with the attached February 7, 

2011 pages 4-28 through 4-30. (Note that June 19, 2006 Appendix C.3 page 4-31 has been 

included for ease of substitution.). 
Rocky Mount, NC 2 

Supplement to the Redesignation Demonstration and Maintenance Plan February 7, 2011 

(This page intentionally left blank)
Rocky Mount, NC 4-1 

Redesignation Demonstration and Maintenance Plan June 19, 2006 

4.0 MOTOR VEHICLE EMISSIONS BUDGET FOR CONFORMITY 

4.1 TRANSPORTATION CONFORMITY 

The purpose of transportation conformity is to ensure that Federal transportation actions 

occurring in nonattainment areas do not hinder the area from attaining and maintaining the 8-

hour ozone standard. This means that the level of emissions estimated by the NCDOT or the 

metropolitan planning organizations for the Transportation Implementation Plan (TIP) and Long 

Range Transportation Plan must not exceed the motor vehicle emission budget (MVEB) as 

defined in this maintenance plan. 

4.2 HIGHWAY MOBILE SOURCE VOC INSIGNIFICANCE 

Section 93.109(k) in the Transportation Conformity Rule Amendments for the new 8-hour ozone 

and fine particulate matter NAAQS addresses areas with insignificant motor vehicle emissions. 

The rule suggests that such a finding would be based on a number of factors, including the 

percentage of motor vehicle emissions in the context of the total SIP inventory, the current state 

of air quality as determined by monitoring data for that NAAQS, the absence of SIP motor 

vehicle control measures, and historical trends and future projections of the growth of motor 

vehicle emissions. 

The NCDAQ has examined the sources of VOC emissions and their contribution to ozone 

formation in North Carolina. Because of the generally warm and moist climate of North 

Carolina, vegetation abounds in many forms, and forested lands naturally cover much of the 

state. The biogenic sector is the most abundant source of VOCs in North Carolina and accounts 

for approximately 90% of the total VOCs statewide. The overwhelming abundance of biogenic 

VOCs makes the majority of North Carolina a NOx limited environment for the formation of 

ozone. This holds true in Edgecombe and Nash Counties. 

Also noteworthy are the projected decreases in highway mobile VOC emissions through the year 

2017 despite projected VMT increases. These reductions are due mainly to the retirement of 

older vehicles and the growing fleet of Tier 2 vehicles on the roads in future years. Some 

additional reductions are attributable to North Carolina’s inspection and maintenance program in 

Edgecombe and Nash Counties. 

Additionally, the NCDAQ has performed a number of modeling sensitivities to determine the 

impact of highway mobile source VOCs on ozone formation in the Rocky Mount area. The 

results of these sensitivities indicate no change in future ozone concentrations in the Rocky 
Rocky Mount, NC 4-2 

Supplement to the Redesignation Demonstration and Maintenance Plan February 7, 2011 

Mount area when highway mobile VOCs are significantly changed. These sensitivities are 

discussed in more detail in Appendix C.3. 

The NCDAQ believes highway mobile VOCs are insignificant contributors to ozone formation 

in the Rocky Mount nonattainment area. Emission estimates indicate highway mobile VOC is a 

small percentage of the total VOC emissions inventory. Highway mobile VOC emissions are 

projected to decrease into the future notwithstanding VMT increases. The area is currently well 

below the NAAQS and emission sensitivity modeling indicates no change in future ozone 

concentrations when VOC emissions are significantly changed. Further, the NCDAQ considers 

it unreasonable to expect that Edgecombe and Nash Counties will experience enough motor 

vehicle emissions growth for a future ozone violation to occur. For these reasons, the NCDAQ 

will not be setting MVEB for VOC for the Rocky Mount area. 

4.3 SAFETY MARGIN 

As stated in Section 3.3.4, a safety margin is the difference between the attainment level of 

emissions from all source categories (i.e., point, area, and mobile) and the projected level of 

emissions from all source categories. The safety margins for the Rocky Mount area are listed in 

Table 3-7 above. The State may choose to allocate some of the safety margin to the MVEB, for 

transportation conformity purposes, so long as the total level of emissions from all source 

categories remains equal to or less than the attainment level of emissions. 

The NCDAQ has decided to allocate safety margin to the MVEB to account for new emissions 

models, VMT projections models, as well as changes to future vehicle mix assumptions, etc. that 

influence the emission estimations. Since 2008 is a historic year, the NCDAQ decided to 

allocate the entire safety margin available to the MVEBs. For 2017, the NCDAQ estimated the 

amount needed to account for the current emission model and VMT projections model and then 

added an additional 21% to account for any future changes to the emission model, projection 

model and other input data. 

Motor Vehicle Emission Budgets

The NCDAQ did not receive any comments regarding the geographic extent of the MVEB from 

any of the Rocky Mount transportation partners during the maintenance plan interagency 

consultation process. However, there was discussion through the interagency consultation 

process on the years to set MVEB for the Rocky Mount maintenance plan. According to Section 

93.118 of the transportation conformity rule, a maintenance plan must establish a MVEB for the 

last year of the maintenance plan (in this case, 2017). Through the interagency consultation 
Rocky Mount, NC 4-3 

Supplement to the Redesignation Demonstration and Maintenance Plan February 7, 2011 

process, it was decided that another MVEB would be set for the year 2008 in the Rocky Mount 

maintenance plan. 

The NCDAQ will set MVEB, for transportation conformity purposes, as county budgets within 

the Rocky Mount maintenance area for 2008 and 2017. Tables 4-1 and 4-2 below list out the 

NOx MVEB, for transportation conformity purposes, by county for the years 2008 and 2017. 

Upon the USEPA’s approval of these county-by-county sub-area MVEB, these MVEB will 

become the applicable MVEB for each county. 

Table 4-1 Edgecombe County MVEB in kilograms per day 

 2008 2017 

NOx Emissions (kg/day)

Base Emissions 2,483 1,143 

Safety Margin Allocated to 

MVEB 1,674 1,108 

NOx Conformity MVEB 4,157 2,251 

Table 4-2 Nash County MVEB in kilograms per day 

2008 2017 

NOx Emissions (kg/day)

Base Emissions 8,790 3,767 

Safety Margin Allocated to 

MVEB 1,655 2,374 

NOx Conformity MVEB 10,444 6,141 

New Safety Margins

A total of 3,329 kg (3.67 tons) and 3,482 kg (3.84 tons) of 2008 and 2017 NOx safety margin, 

respectively, were added to the MVEB for the Rocky Mount area. Taking into consideration the 

portion of the safety margin applied to the MVEB the resulting difference between the 

attainment level of emissions from all sources and the projected level of emissions from all 

sources in the maintenance area, i.e., the new safety margins, for each projected year is listed 

below in Table 4-3. 
Rocky Mount, NC 4-4 

Supplement to the Redesignation Demonstration and Maintenance Plan February 7, 2011 

Table 4-3 New Safety Margins for the Rocky Mount Area 

Year VOC TPD NOx TPD 

2005 N/A N/A 

2008 -0.59 0.0 

2011 -0.51 -6.93 

2014 -0.07 -9.77 

2017 -0.07 -7.79 
Mobile Source Inventory Appendix C.3 4-28 

Supplement to the Rocky Mount 8-hour Ozone Maintenance Plan February 7, 2011 

Based on the information discussed above, the NCDAQ steadfastly believes highway mobile 

VOCs are insignificant contributors to ozone formation in Edgecombe and Nash Counties. 

Emission estimates indicate highway mobile VOC is a small percentage of the total VOC 

emissions inventory. Highway mobile VOC emissions are projected to decrease into the future 

notwithstanding VMT increases. The area is currently well below the NAAQS and emission 

sensitivity modeling performed by ASIP and the NCDAQ indicates no change in future ozone 

concentrations when VOC emissions are significantly changed. Further, the NCDAQ considers 

it unreasonable to expect that Edgecombe and Nash Counties will experience enough motor 

vehicle emissions growth for a future ozone violation to occur. For these reasons, the NCDAQ 

will not be setting MVEB for VOC for the Rocky Mount area. 

Safety Margin

A safety margin is the difference between the attainment level of emissions from all source 

categories (i.e., point, area, and mobile) and the projected level of emissions from all source 

categories. The State may choose to allocate some of the safety margin to the MVEB, for 

transportation conformity purposes, so long as the total level of emissions from all source 

categories remains equal to or less than the attainment level of emissions. 

The NCDAQ has decided to allocate safety margin to the MVEB to account for new emissions 

models, VMT projections models, as well as changes to future vehicle mix assumptions, etc. that 

influence the emission estimations. Since 2008 is a historic year, the NCDAQ decided to 

allocate the entire safety margin available to the MVEBs. For 2017, the NCDAQ estimated the 

amount needed to account for the current emission model and VMT projections model and then 

added an additional 21% to account for any future changes to the emission model, projection 

model and other input data. 

Motor Vehicle Emission Budgets

The NCDAQ did not receive any comments regarding the geographic extent of the MVEB from 

any of the Rocky Mount transportation partners during the maintenance plan interagency 

consultation process. However, there was discussion through the interagency consultation 

process on the years to set MVEB for the Rocky Mount maintenance plan. According to Section 

93.118 of the transportation conformity rule, a maintenance plan must establish a MVEB for the 

last year of the maintenance plan (in this case, 2017). Through the interagency consultation 

process, it was decided that another MVEB would be set for the year 2008 in the Rocky Mount 

maintenance plan. 
Mobile Source Inventory Appendix C.3 4-29 

Supplement to the Rocky Mount 8-hour Ozone Maintenance Plan February 7, 2011 

The NCDAQ will set MVEB, for transportation conformity purposes, as county budgets within 

the Rocky Mount nonattainment area for 2008 and 2017. Tables 4.1.6-1 and 4.1.6-2 below list 

out the NOx MVEB, for transportation conformity purposes, by county for the years 2008 and 

2017. Upon the USEPA’s approval of these county-by-county sub-area MVEB, these MVEB 

will become the applicable MVEB for each county. 

Table 4.1.6-1 Edgecombe County MVEB in kilograms per day 

 2008 2017 

NOx Emissions (kg/day)

Base Emissions 2,483 1,143 

Safety Margin Allocated to 

MVEB 1,674 1,108 

NOx Conformity MVEB 4,157 2,251 

Table 4.1.6-2 Nash County MVEB in kilograms per day 

2008 2017 

NOx Emissions (kg/day) 

Base Emissions 8,790 3,767 

Safety Margin Allocated to 

MVEB 1,655 2,374 

NOx Conformity MVEB 10,444 6,141 
Mobile Source Inventory Appendix C.3 4-30 

Supplement to the Rocky Mount 8-hour Ozone Maintenance Plan February 7, 2011 

(This page intentionally left blank)
Mobile Source Inventory Appendix C.3 4-31 

Rocky Mount 8-hour Ozone Maintenance Plan June 19, 2006 

4.1.7 Speed and VMT provided in January 11, 2006 email from NCDOT 

EDGECOMBE COUNTY

Modeled Area

Functional Class>Code 2002 2010 2020 2030

U-Inter>11 0 0 0 0

Frwy/Exway>12 96,183 132,442 145,217 181,269 

U-OtherPrincipal>13 18,434 21,299 23,253 26,477 

U-MinorArterial>14 95,164 112,033 150,093 178,359 

Collector>15 14,935 17,097 18,254 19,974 

U-Local>18 50,229 63,048 72,449 84,957 

R-Inter>21 - - - - 

R-OtherPrincipal>23 130,368 195,824 249,218 321,288 

R-MinorArterial>24 8,061 8,455 9,395 10,339 

MajorCollector>26 106,438 85,241 106,833 137,766 

MinorCollector>27 60,680 66,977 75,900 100,975 

R-Local>28 71,333 87,077 97,925 111,287 

Total from Model 651,825 789,495 948,535 1,172,690 

Rural spreadsheet Portion 851,465 1,042,781 1,249,659 1,456,538 

County total 1,503,290 1,832,275 2,198,194 2,629,229

County total from Universe file 1,548,100 1,895,942 2,272,058 2,648,173 

2002 2010 2020 2030

Rural VMT(Outside MPO)

Urban Interstate 0.0 0.0 0.0 0.0

Urban Other Freeway 44,399.5 67,744 81,184 94,624 

Urban Other PA 53,540.0 65,312 78,270 91,227 

Urban Minor Arterial 72,580.5 101,020 121,062 141,103 

Urban Collector 8,768.0 11,533 13,822 16,110 

Urban Local 40,677.5 50,167 60,120 70,072 

Rural Functional Classes

Rural Interstate 0.0 0.0 - - 

Rural Other PA 196,647.0 235,449 282,160 328,871 

Rural Minor Arterial 73,139.0 90,089 107,962 125,834 

Rural Major Collector 197,092.5 217,920 261,154 304,387 

Rural Minor Collector 104,681.5 131,202 157,232 183,261 

Rural Local 59,939.0 72,343 86,695 101,048 

Total 851,464.50 1,042,781 1,249,659 1,456,538 
Hearing Record Appendix B 14 

Supplement to the Rocky Mount 8-Hour Ozone Maintenance Plan February 7, 2011 

Public Notice Report 

For the Supplement to the Redesignation Demonstration and 

Maintenance Plan for the Rocky Mount, North Carolina 

8-Hour Ozone Nonattainment Area 

On December 3, 2010, a draft version of the North Carolina supplement to the redesignation 

demonstration and maintenance plan for the Rocky Mount, North Carolina 8-hour ozone 

nonattainment area was submitted to the U. S. Environmental Protection Agency (USEPA). A 

request for public hearing, in accordance with 40 CFR 51.102, and the public comment period 

were noticed in the local newspapers on Wednesday, December 8, 2010. The public comment 

period was open from December 8, 2010, through January 10, 2011. No request for public 

hearing was received and no public comments were received. 

In March 2010, the USEPA announced in the Federal Register (FR) that the new mobile model, 

Motor Vehicle Emission Simulator (MOVES), will be required for transportation conformity 

purposes starting March 2012 (40 FR 9411). The NCDAQ committed to the transportation 

partners to review and revise the motor vehicle emission budgets if necessary to account for 

changes to the emission models, to the vehicle miles traveled projection models and other 

emission model input data. This supplement revises the motor vehicle emission budgets through 

the allocation of a portion of the safety margin. These revised motor vehicle emission budgets 

will be used for transportation conformity purposes once approved by the USEPA. 

The North Carolina Division of Air Quality will be moving forward with the final submittal to 

the USEPA of the North Carolina supplement to the redesignation demonstration and 

maintenance plan for the Rocky Mount, North Carolina 8-hour ozone nonattainment area. 
Hearing Record 

Supplement to the Rocky Mount 8-Hour Ozone Maintenance Plan

Appendix B 15 

February 7, 2011
Hearing Record 

Supplement to the Rocky Mount 8-Hour Ozone Maintenance Plan

Appendix B 16 

February 7, 2011
Hearing Record 

Supplement to the Rocky Mount 8-Hour Ozone Maintenance Plan

Appendix B 17 

February 7, 2011
Hearing Record 

Supplement to the Rocky Mount 8-Hour Ozone Maintenance Plan

Appendix B 18 

February 7, 2011