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

Notes

1 All MOBILE6 simulations done in this study used the version publicly available in September 2003, known as MOBILE6.2, which was the version available at the beginning of the study. In late November 2003, EPA released a new version of MOBILE6.2, called MOBILE6.2.03 (version dated September 24, 2003). This newer version was adjusted to account for effects of Tier2 and the National Low Emission Vehicle program standards. A comparison between the version used in this study and the newly released version showed that in all cases the newer version of the model produced lower CO emission rates. This implies that the results found in this study are conservative, in that they underestimate the emission reduction effects estimated in the latest version of MOBILE6 (6.2.03) in comparison to MOBILE5.

2 All MOBILE6 simulations done throughout this study used the version publicly available in September 2003, known as MOBILE6.2, which was the version available at the beginning of the study. In late November 2003, EPA released a new version of MOBILE6.2, called MOBILE6.2.03 (version dated September 24, 2003). This newer version was adjusted to account for effects of Tier2 and the National Low Emission Vehicle program standards. A comparison between the version used in this study and the newly release version showed that in all cases the newer version of the model produced lower CO emission rates. This implies that the results found in this study are conservative, in that they underestimate the emission reduction effects estimated in the latest version of MOBILE6 (6.2.03) in comparison to MOBILE5.

3 For example, use of MOBILE6 may show higher emissions at intersections near a park-and-ride lot compared to previous MOBILE versions due to more explicit recognition of cold starts under certain conditions.

4 All MOBILE6 simulations done throughout this study used the version publicly available in September 2003, known as MOBILE6.2, which was the version available at the beginning of the study. In late November 2003, EPA released a new version of MOBILE6.2, called MOBILE6.2.03 (version dated September 24, 2003). This newer version was adjusted to account for effects of Tier2 and the National Low Emission Vehicle program standards. A comparison between the version used in this study and the newly release version showed that for most national default fleets in 2005 that LDGV, LDGT12 had about 8% lower emissions for all speeds with the new version of the model, while LDGT34 and LDDV had only a 1-3% reduction. These effects changed in later years, by 2035 LDGV vehicles show a 5-8% decrease, LDGT12 and LDGT34 show a 16-22% decrease, and LDDV a 9% decrease. This implies that the results found in this study are, in general, conservative, in that they underestimate the emission reduction effects estimated in the latest version of MOBILE6 (6.2.03) in comparison to MOBILE5.

5 Some revision to these estimates may occur later this year with the anticipated release in late 2004 of the2004 Parking Generation manual by the Institute of Transportation Engineers.

6 This results in some cases where future-year temperature/speed combinations maximum "increment" is different than the base year.

7 This relatively low freeway speed was chosen as representative of a typical congested freeway condition. It should also be noted that for MOBILE6, CO emission factors increase with speed after 35 mph. Thus the 48.3 mph emission factor is about equivalent to the 20 mph emission rate; 65 mph is equivalent to the 12 mph emission rate.

8 Cold start emissions were simulated in MOBILE6 by setting all soak times to 720 minutes. Hot-stabilized emissions had all soak times set to 10 minutes.

9 These 2005 concentration increases would be about 20% higher at higher speeds (65mph) if the same level of traffic volume was possible.

10 This refers to the classification of signalized intersection operations based on procedures in the Highway Capacity Manual. The ratings go from LOS A, with little delay, to LOS F, with an average delay over 80 s per vehicle.

11 This factor takes into account variations in traffic and meteorological conditions between the 1 and 8-hour averaging periods.

12 This refers to the classification of signalized intersection operations based on procedures in the Highway Capacity Manual. The ratings go from LOS A, with little delay, to LOS F, with an average delay over 80 s per vehicle.

13 EPA, 2002. "Technical Guidance Use of MOBILE6 for Emission Inventory Preparation", EPA/OTAQ, January 2002, pg. 42.

Updated: 07/06/2011
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