Transportation Conformity Reference Guide

Section D: Specific Regional Analysis Requirements
Chapter 11 NO₂ Nonattainment and Maintenance Areas

Modeling Requirements for NO₂ Nonattainment and Maintenance Areas
Criteria and Procedures for Determining Conformity for NO₂ Nonattainment and Maintenance Areas

Exhibit 11-1: Actions & Tests for NO₂ Nonattainment & Maintenance Areas

In addition to the regional analysis criteria and requirements applied to all areas at all times (as discussed in Chapter 5), and in order to demonstrate conformity, NO2 nonattainment and maintenance areas are required to follow these specific criteria, as stated in the transportation conformity rule,

40 CFR §93.122(d)

In all areas not otherwise subject to paragraph (b) of this section, regional emissions analysis must use those procedures described in paragraph (b) of this section if the use of those procedures has been the previous practice of the MPO. Otherwise, areas not subject to paragraph (b) of this section may estimate regional emissions using any appropriate methods that account for VMT growth by, for example, extrapolating historical VMT or projecting future VMT by considering growth in population and historical growth trends for VMT per person. These methods must also consider future economic activity, transit alternatives, and transportation system policies.

Areas without network models may project vehicle miles traveled (VMT) using any appropriate methods that account for VMT growth by, for example, extrapolating historical VMT or projecting future VMT by considering growth in population and historical growth trends for VMT per person. These methods must also consider future economic activity, transit alternatives, and transportation system policies. All VMT estimates must be "calibrated" to HPMS. Also, all methods related to VMT estimations must be decided through interagency consultation.

40 CFR §93.122(b)(3)

Highway Performance Monitoring Systems (HPMS) estimates of vehicle miles traveled (VMT) shall be considered the primary measure of VMT within the portion of the nonattainment or maintenance area and for the functional classes of roadways included in HPMS, for urban areas which are sampled on a separate urban area basis. For areas with network-based travel models, a factor (or factors) may be developed to reconcile and calibrate the network-based travel model estimates of VMT in the base year of its validation to the HPMS estimates for the same period. These factors may then be applied to the model estimates of future VMT. In this factoring process, consideration will be given to differences between HPMS and network-based travel models, such as differences in the facility coverage of the HPMS and the modeled network description. Locally developed count-based programs and other departures from these procedures are permitted subject to the interagency consultation procedures of §93.105(c)(1)(i).

Modeling Requirements for NO₂ Nonattainment and Maintenance Areas

The requirements for regional analysis in NO₂ nonattainment and maintenance areas are listed below:

• There are no network-based travel modeling requirements. However, areas already using travel demand modeling or network based travel models must continue to do so, and must follow the six network-based modeling requirements as stated in 40 CFR §93.122(b)(1)(i)-(vi), and described in Chapter 8.
• All areas not using network-based models are required to use best professional practice to account for VMT estimates such as HPMS or locally-based count programs, with the method used determined through the interagency consultation process.

Criteria and Procedures for Determining Conformity for NO₂ Nonattainment and Maintenance Areas

In addition to the criteria listed in 40 CFR §93.109(b) - Table 1 of the transportation conformity rule, the conformity determination in a NO₂ nonattainment area is also based on the criteria specific to the nonattainment area, which are summarized in Exhibit 11-1. In short, NO₂ nonattainment areas have the option to use either the build/no-build test or no-greater-than-1990 test to determine conformity, provided they have not submitted a control strategy SIP or maintenance plan with adequate or approved motor vehicle emissions budgets. Detailed discussion of these requirements is provided in the transportation conformity rule and in Chapter 5 of this document.