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Implications of the Implementation of the MOBILE6 Emissions Factor Model on Project-Level Impact Analyses Using the CAL3QHC Dispersion Model

Appendix C: Interview Questions

How Use of MOBILE6 Has Changed Results Relative to MOBILE5

General

Does your agency perform the MOBILE6 modeling necessary for project-level analyses, or is this modeling performed by consultants, the State air agency, or some other party?

Do you have thresholds or a screening procedure to determine when hotspot modeling is necessary for a project, or do you rely on the default LOS C threshold in the conformity rule?

What are your "worst case" conditions for your location/practice/research? For instance, what would you use in your screening analysis for temperature, starts, background, and persistence factors?

Vehicle Fleet Characteristics

Have you made use of the more specific vehicle fleet characteristics options in MOBILE6 [e.g., have you used local data on vehicle age, registration distribution, mileage accumulation, alternative diesel sales fraction, or natural gas vehicle fractions]? If so, how have these changes impacted the resulting emission factors relative to what you would have found if you only used MOBILE5? Will you use different vehicle fleets for different projects in your area, and what criteria would you base this on?[If they have made use of specific vehicle fleet characteristic changes then proceed with the remaining questions in this section.]

Have you gathered local data for the 28 individual vehicle types used in the MOBILE6 fleet characteristics commands? Or have you alternatively mapped the MOBILE5 categories to MOBILE6? If so, how did you decide on the mapping? Did you use the methodology in the MOBILE6 Technical Guidance?

Are you making use of the registration distribution capability in MOBILE6 for any of the 16 composite vehicle types for the 25-year vehicle age distributions? If so, which vehicle types and why these? How did you gather the data on vehicle type and age? In particular how are you handing the heavy-duty gasoline vehicle registration that is now composed of 8 types, whereas MOBILE5 only had 1?

Are you making use of the 14 composite vehicle type diesel fraction splits for the 25-year vehicle ages? If so, for which vehicles and why these? How did you gather the data on diesel fraction splits by age?

Are you making use of the r natural gas vehicle fractions?

Are you specifying annual mileage accumulation rates for any of the 28 individual vehicle types? If so, which vehicles and why these? How did you gather the information on mileage accumulation?

If you are using local registration data to establish vehicle class distributions, do you account for corridor-to-corridor variability or external traffic passing through the study area?

Vehicle Activity

Have you made use of local vehicle activity options (i.e., VMT fleet mix by vehicle type, VMT distribution by hour, VMT Distribution by facility type, VMT by speed distribution, and average speed in MOBILE6)? If so, how have these changes impacted the resulting emission factors relative to what you would have found if you only used MOBILE5?[If they have made use of specific vehicle activity changes then proceed with the remaining questions in this section]

Are you basing your project-level studies on vehicle classification counts (VMT fleet mix) within the project area? How many categories are distinguished in your counts?

How are you projecting traffic counts to future study years on existing roadways or onto proposed facilities? How are you establishing the fleet characteristics (VMT fleet mix) for these future cases (i.e., are you using the same fleet characteristics for future cases as the present)?

Are you specifying local vehicle miles traveled by vehicle type for each of the 16 composite vehicle types? If so, which vehicles and why these? How did you gather the information on vehicle type? Are you using the MOBILE6 User Guide suggested mapping?

Are you specifying local vehicle miles traveled by the specific facility type in the project-level analysis? By each hour of the day? Or using peak hour? If so, which facilities and why these?

Are you specifying local vehicle miles traveled by speed for the two facility types that allow speed variations? If so, which facilities did you specify and why these?

How do you gather the information on the 14 speed distributions? By facility? By time of day? Are you using the MOBILE5 speeds to create MOBILE6 speeds by facility types as suggested in Appendix F of the MOBILE6 User Guide?

Do you use a locally developed estimate of speed for the "local" and "ramp" facility types, or do you rely on the MOBILE6 defaults? How do you account for speeds other than the default?

Is your standard practice to use the "Average Speed" command in the project-level analysis to calculate emission factors as a function of vehicle speed for the two facility types that allow speed variations?

Operating Modes

Have you made use of local operating mode options (i.e., starts per day, start distribution, soak time distribution, weekend/weekday trip length distribution and weekend vs. weekday activity) in MOBILE6? If so, how have these changes impacted the resulting emission factors relative to what you would have found if you only used MOBILE5?[If they have made use of specific operating mode changes then proceed with the remaining questions in this section]

Are you using local start emissions in your project-level analysis even in light of EPA's recommendation13 that the calculation of idling emissions at intersections not include any effects from engine starts? Does your practice for including or not including start emissions vary by location of the project? (See examples from Task 5 of the SOW.) If so, are you relying on the model's default assumptions on start activity (starts per day, start distribution, soak distribution) or using local data?

If you are using local data, how did you determine the number of starts per day for the up to 18 individual vehicle classes affected by starts per day? Did you differentiate between weekday and weekend starts? If so, how did you determine this?

If you are using local data for start emissions, how did you determine the hourly start distribution? How did you collect this information for use in the model? How did you use it in the model? Does it differ between weekday and weekend? If so, how did you determine this?

If you are using local data for start emissions, are you providing project-level specific vehicle soak distributions? If so, how do they differ from the national default? How did you determine the hourly soak distributions for the 70 soak duration values? Do you differentiate between weekday and weekends?

Are you making use of the weekend/weekday trip length distribution or the weekend vs. weekday activity in your project-level analyses? If so, how?

External Conditions

Have you made use of the expanded meteorological conditions options (i.e., min/max temperature and hourly temperature) in MOBILE6? If so, how have these changes impacted the resulting emission factors relative to what you would have found if you only used MOBILE5?[If they have made use of the expanded meteorological condition options, then proceed with the two questions in this section]

Are you making use of the hourly temperature feature in MOBILE6? Do you use the max/min temperature parameter and specify the same temperature?

How local are your temperature data (e.g., County level), and what is the source of the data? [Note, areas subject to conformity should be using temperature data consistent with that used for the regional emissions analysis, per section 93.123(c)(3) of the conformity rule, which in turn should be consistent with the data used to develop the SIP emissions budgets (93.122(a)(6)). If areas subject to conformity are using project-specific temperature data that differ from the SIP inputs, then we will ask the reason, and ask if this was cleared through the interagency consultation process.

State Programs

Are you making use of the ability of MOBILE6 to incorporate up to seven different exhaust and evaporative emission I/M programs on calculated emission factors? If so, how many are you using? How do you determine the appropriate mix for the project location? Are there features not available in MOBILE6 I/M options that you would like to see? If so, what are they and why are they important?

Fuels

Are you making use of any of the new MOBILE6 capabilities for RVP   specification, as well as lower bound range for RVP specification in your project-level analysis? Are you using the "splash" blend capability for alcohol-based oxygenates? Have you estimated how these capabilities have affected project-level emissions? Are there features not available in MOBILE6 fuel options that you would like to see? If so, what are they and why are they important.

General Impacts

Have you found changes in idle emission rates as a result of the changes you have adopted for use with MOBILE6? If so, can you provide an estimate of the change in the idle emission rate, as well as the implementing change used in MOBILE6?

How would you characterize your "worst case" events for project-level analysis in your region? What are the associated parameters for those conditions (i.e., meteorological conditions, traffic operations, fuel mix, temperature, etc.)?

How Use of MOBILE6 Has Changed the Project-level Process

Has the use of MOBILE6 required a need to gather additional information? If so, how much additional resources/time is needed to perform a typical MOBILE6 analysis? Will this effort require less time/fewer resources as the user gains more familiarity with MOBILE6?

Has the use of MOBILE6 led to the need to involve additional agencies in preparing model inputs? For example, is additional information now needed from air agencies on fuel programs, I/M, meteorology? Department of motor vehicle registration on vehicle fleet and age distribution? Have other processes of preparing inputs been affected by the use of MOBILE6?

Has the application of MOBILE6 affected procedures unique to any additional state or local requirements for project-level analyses?

Has the change to MOBILE6 caused your screening procedures to be reassessed? If so, how have they changed? Are trigger levels now higher or lower than with MOBILE5? For example, has MOBILE6 changed the traffic volume trigger screening-levels?

Has the use of MOBILE6 had any impact on possible CO mitigation strategies? If so, how has it changed the strategies?

Has the use of MOBILE6 caused you to revisit how you've estimated present and future background carbon monoxide concentration? What is your procedure for estimating present and future background concentration, and if it was modified due to MOBILE6, how has it changed?

Updated: 07/06/2011
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