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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 D: Interview Summary Table

Background Questions

Has M6 Changed Analysis Process?

Has M6 Changed Results
of Project-level Analysis

Do you use M6 for Project-level analysis?

Is hotspot modeling based on thresholds or LOS C?

What are your worst case conditions?

Need for additional information

Need to involve additional agencies

Affect on state/ local procedures

Change in estimate for present/ future back-ground CO due to M6

Reassessed screening procedures due to M6

Impact on CO mitigation strategies


All respondents in which a full interview was conducted use Mobile 6 in project-level analysis.

Most use consultants with some of the M6 work done by APCD or state enviro agency.

M6 is better designed for area wide analysis (such as inventories, mesoscale analysis) rather than the microscale analysis.

Many questions related to applicability of M6 for project-level analysis.

Five of the nine agencies use a modification of the LOS C screening procedures consisting of LOS and volume thresholds.

Four of the nine agencies use LOS C, but two indicate revising this procedure

Most agencies use peak hour traffic volumes

Most use a persistence factor (p.f.) of 0.7; however the range was from 0.72 to 0.57 depending on local data used to develop p.f.

Most agencies use January average temperatures, these may be refined to county or locally specific temperatures

.Background CO is determined in various ways - no consistent approach - statewide uniform value, varying values across the state, local monitoring data, roll forward, and SIP modeling

For CAL3QHC modeling follow EPA roadway intersection guidance

M6 allows optional inputs/local data. About half the agencies would like to develop these inputs

This additional information requires more survey and statistical analysis assessment primarily for:

vehicle mix distribution and; vehicle class

Would like to see sensitivity test of the model and impacts of the inputs.

Other half of agencies did not see the need for additional information-using national defaults

About half the agencies indicated that additional contact and coordination was needed with APCD, MPO, and energy departments

The other half of the agencies indicated that the same agencies are needed as with M5

The need for additional contact were those agencies making use of the M6 options which had previously relied on national defaults

Most agencies responded that M6 has had no change on their state and local procedures

A few cited the need for expanded coordination throughout the process to get local data for each analysis

 In general agencies have not found that M6 has caused any change to the present background concentration.

Several agencies are looking to possibly use M6 for future year emissions which will impact the roll forward or trends to estimate future background concentration.

Six of the nine agencies report no changes to the screening procedures.

Three agencies are updating the screening procedures to incorporate M6 inputs.

Most agencies felt it was to earlier to tell the impact on mitigation strategies. However, one agency strongly suspects that one intersection which had previously shown a problem with M5 requiring mitigation will no longer be the case when using M6.


Three researchers were interviewed which heavily use M6 for project-level analysis.

All three researchers use it in private consulting projects for project-level analysis.

All three researchers use a screening approach, but these are tied to the particular state or local agency.

Trigger requirement varies state by state, agency by agency.

1) Project related volume increases over no-build scenario is usual determining factor.

2) Some agencies first look at LOS D, E, and F, and then at volume increases.

3) Delay increases over no-build are also used

Temperature determination is either based on average temperature of top 10 CO readings during last 3 years, or the one used for current SIP, or specified by state as January climate average.

M6 default values used for base traffic, with exception for project specific generated outbound trips (i.e. out of parking lots or buildings)

Persistence factors are usually based on top 10 eight-hour/ one-hour CO measurements during last 3 years or specified by state

CO background are specified by state

Amount of additional information is generally small (i.e. roadway type, mileage accumulation),

However, if all M6 features are employed the additional information required are extensive

At first, M6 is more time consuming to prepare input files, since VMT fractions, soak distributions, and other parameters are not as simple as M5. However, once done a few times, the process becomes simpler.

Same agencies as used in M5 applications are needed.

In general impacts were seen in the data collection process, application to facility specific types, and in the hot/cold start specifications

Many states just use average monitoring concentration of last three years for background levels.

Many states are recalculating M6 with future backgrounds levels using the roll forward technique.

Yes, researches saw the need to revisit screening procedures as M6 coupled with CAL3QHC does not produce same results

 Much smaller differences between cold start and hot-stabilized.

Speed curves for CO are U-shaped with lowest point around 30-35 mph.

Idle emissions play much smaller role when compared to moving (cruise) emissions.

Worstcase modeling receptors change from intersection to mid block

An interchange or non-signalized intersection can have higher CO impacts than a signalized intersection

Increasing capacity to achieve higher speeds is no longer desirable and won't solve problems.

Optimizing signal timing will have to be studied further to better quantify possible benefits

Updated: 3/17/2015
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