Input Guidelines for Motor Vehicle Emissions Simulator Model, Volume 2: Practitioners’ Handbook: Project Level Inputs (2015)

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3.0 Sensitivity of Model Outputs to Inputs The sensitivity of MOVES outputs to inputs can be characterized as the percent change in a pollutant output corresponding to a change in the input value across a range of condi- tions representative of the real world. This section provides a summary of sensitivity analyses conducted on the various MOVES inputs. The findings are based on research performed by the Volpe National Transportation Systems Center and Federal Highway Administration (FHWA),4 EPA staff,5 and the Coordinating Research Council (CRC),6 as well as additional sensitivity analysis performed for this study, as described in the NCHRP Project 25-38 Final Report. In addition to overall sensitivity for each input parameter, in some cases, sensitivity was examined for providing different data for differ- ent source types (e.g., different speed distributions for trucks versus cars). Table 3.1 provides a summary of MOVES inputs by sensitivity level. It takes the worst case result for each MOVES input observed in the various studies, and assigns it to one of four sensitivity ranges. This is done separately for volatile organic compounds (VOC), oxides of nitrogen (NOx), and PM. In general temperature, vehicle-miles of travel (VMT), speed, age, and population have either substantial or very substantial sensitivity for all three pollutants. The data sources that are critical for these inputs include registration data for age and population inputs; classified traffic counts and travel demand models for VMT; and real-world and/or modeled speed data. Month and hour VMT fraction inputs (based on seasonal and hourly traffic data) have modest sensitivity for all pollutants. Ramp fraction, source type detail for road type distributions, and speeds have different sensitivity depending on the pollutant of concern. Table 3.2 lists the various MOVES inputs along with a summary of the range (variation) in expected outputs under a typical range of input conditions tested in the various studies. Effects on five key pollutants, including VOC, CO, NOx, PM, and carbon dioxide (CO2), are presented. 4 Noel, G., and R. Wayson (2012). “MOVES2010a Regional Level Sensitivity Analysis.” Volpe National Transportation Systems Center, prepared for Federal Highway Administration, DOT- VNTSC-FHWA-12-05. 5 Choi, D., et al (undated). “MOVES Sensitivity Analysis: The Impacts of Temperature and Humidity on Emissions.” U.S. Environmental Protection Agency. 6 Eastern Research Group (2014). “Study of MOVES Inputs for the National Emissions Inventory.” Prepared for Coordinating Research Council Project A-84. 3-1

All of these sensitivity analyses were conducted using some version of MOVES2010. There may be minor differences in some impacts if the same analyses were conducted using MOVES2014, due to differences in embedded data in MOVES2014. The overall con- clusions about the sensitivity of the model to each input, however, should not change significantly. Table 3.1 Summary of MOVES Inputs Falling in Different Sensitivity Ranges Sensitivity Range VOC NOx PM Very Substantial (>50%) Temperature, Speed, Age Temperature, VMT, Speed Temperature, VMT, Speed Substantial (15-50%) Population, VMT Population, Age, Humidity Population, Age, Ramp Fraction Moderate (5-15%) None None Source type detail for road type distance and speed Modest (<5%) Source type detail for road type distance and speed, Month VMT Fraction, Hour VMT Fraction, Ramp Fraction Source type detail for road type distance and speed, Month VMT Fraction, Hour VMT Fraction, Ramp Fraction Month VMT Fraction, Hour VMT Fraction, Humidity Note: The worst case sensitivity results are used for assigning inputs to the ranges in this table. 3-2

Table 3.2 Combined Sensitivity Analysis Results MOVES Input Source Base Case Comparison Made VOC NOx PM Fleet Inputs Age Distribution by Vehicle Class Volpe/FHWA 2010 National Default Age Distribution Move 10% of vehicles to Group 1 (0-10 years); Move 10% of vehicles to Group 2 (11-20 years); Move 5% of vehicles to Group 3 (21-30 years); completed for several vehicle types PC: Substantial (-29% to +24%) CT: Moderate (-5% to +6%) PC: Substantial (-20% to +16%) CT: Moderate (-9% to +9%) PC: Substantial (-19% to +21%) CT: Moderate (-7% to +7%) Age Distribution by Vehicle Class ERG/CRC Submittals for 2011 NEI Increase average age from 10th to 90th percentile Very Substantial (+55% HC) Substantial (+40%) Substantial (+45%) Source (Vehicle) Type Population: Light versus Heavy-Duty Vehicles CS/ERG 2010 National Default Source Type Distribution Double HD vehicles and reduce LD vehicles correspondingly Moderate (+7%) Substantial (+36%) Very substantial (+66%) Passenger Cars versus Trucks Shift 20% of passenger vehicles from cars (21) to trucks (31) Modest (+2%) Modest (+1%) Modest (+1%) Single-Unit versus Combination Trucks Shift 25% of trucks from single unit to combination Modest (+2%) Moderate (+14%) Substantial (+23%) Short-Haul versus Long-Haul Trucks Shift 25% of trucks from short-haul to long-haul Modest (+2%) Moderate (+8%) Moderate (+10%) Source (Vehicle) Type Population: ERG/CRC Submittals for 2011 NEI Increase source type fraction of total population from 10th to 90th percentile Substantial (+45% HC) Moderate (+14%) Moderate (+14%) Project-Level Inputs Project-Level Link Activity Volpe/FHWA TBD Off-Network Data Volpe/FHWA TBD 3-3

Table 3.2 Combined Sensitivity Analysis Results (continued) MOVES Input Sourcea Base Case Comparison Made VOC NOx PM Project-Level Inputs (continued) Link Characteristics: Grade CS/ERG 0% Grade, Urban Restricted and Unrestricted Road Types, 30 mph -6%, -4%, -2%, +2%, +4%, +6% grade 2%: Substantial (-15% to +22%) 6%: Substantial to very substantial (-36% to +92%) 2%: Substantial (-26% to +33%) 6%: Substantial to very substantial (-58% to +118%) 2%: Substantial (-27% to +41%) 6%: Very substantial (-55% to +175%) Link Source Types (Hour Fraction) TBD Other Inputs Weather – Meteorology Data Volpe/FHWA 60º F -40º, -20º, 0º, 20º, 40º, 60º, 80º, 100º, 120º F Running: PC: Substantial above 60º F (up to 17%); no impact below. CT: No impact Starts: Substantial below 80º F; no impact above Running: Substantial between 40 and 100º F (-20% to +32%); no impact outside that range Starts: Very Substantial at all temps below 80º F (>100%) PC: Very substantial below 60º F (>100%); no impact above 80º F CT: Modest (<0.1%) Volpe/FHWA 50% Relative Humidity 0%, 20%, 40%, 50%, 60%, 80%, 100% (NOx at 60º F and 80º F, all others at 80º F) PC: Modest (-1% to +2%) CT: Modest (<1%) Moderate (-12% to +15%) Modest (<1%) EPA 75º F -40º F to 120º F in 10º increments; Calendar years 2005, 2015, and 2025 Very substantial for gasoline (~+50-70%), Substantial for diesel (~+10-30%) at 20º F Moderate for gasoline (~+5-8%, Substantial for diesel (~+15-18%) at 20º F Very substantial (~+400- 600% at 20º F) for gasoline Modest (<1%) for diesel EPA 0% Relative Humidity 0-100% relative humidity in 10% increments for 6-12 different temperatures Modest (up to ~+5%) Substantial (up to ~-25%) Modest (<1%) Inspection/Maintenance (I/M) Programs N/A Fuel Formulation and Supply N/A a EPA Choi (undated); ERG/CRC = ERG (2014); Volpe/FHWA = Noel & Wayson (2012); CS/ERG = NCHRP Project 25-38 Final Report (2014) Note 1: Modest = <5 percent; Moderate = 5-15 percent; Substantial = 15-50 percent; Very Substantial = >50 percent. Note 2: Unless noted, Volpe/FHWA results are for running emissions for passenger cars (PC) and combination trucks (CT). CS/ERG results are for combined vehicle fleet and all processes. EPA results are for gasoline versus diesel for all source types. 3-4