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Modifying Link-Level Emissions Modeling Procedures for Applications within the MOVES Framework

5.0 Model Outputs

MOVES outputs from the model runs performed during this study are summarized in this section. These include the TDM-based and HPMS-based model runs originally performed for each of the eight counties in the Houston-Galveston non-attainment area, as well as the model runs conducted for the same region and VMT bases using the alternate Kansas City drive cycles described above in Section 4. These outputs are described in additional detail below.

5.1 Comparison of MOVES Outputs to MOBILE-6 Based Inventory

First, ERG compared the two sets of MOVES runs conducted using the default drive cycles to the original TTI MOBILE6 based inventory 29, which was previously described in detail in Section 2.0. Table 5-1 presents ERG's modeled TDM-based and HPMS-based MOVES model outputs, along with TTI's MOBILE6 inventory emissions in tons, by county, for a Non-School ozone season weekday. Table 5-2 presents the percent difference between both sets of MOVES runs and the original TTI inventory. Note that according to these tables, MOVES is calculating significantly higher NOx emissions across the board, regardless of the VMT basis used for model inputs. There is a wider variance in emissions for CO and VOC; counties with relatively few VMT return a decrease in CO and VOC, while counties with more VMT are associated with a significant increase in CO and VOC. The largest county (in terms of both VMT and population), Harris county, demonstrates much higher emissions of all three pollutants of interest relative to the MOBILE6 inventory.

Note that generally, as shown in Table 5-1, the HPMS VMT being modeled is somewhat higher (for most counties) relative to the modeled MOBILE6 inventory, which in turn leads to higher emissions relative to that same inventory. We conclude here that it's very important, regardless of the VMT basis chosen for calculation, for users to be sure that their activity data is representative, since the model outputs are highly sensitive to it.

Table 5-1. Summary of VMT and Tons of Emissions, by County, Non-school Ozone Season Weekday

  ERG MOVES, TDM-based VMT ERG MOVES, HPMS-based VMT TTI MOBILE6 Inventory
County VMT VOC CO NOx VMT VOC CO NOx VMT VOC CO NOx
Brazoria 5,708,326 4.233 46.032 11.457 5,810,915 4.427 47.051 12.852 5,728,510 3.659 47.044 8.704
Chambers 2,508,488 0.950 17.900 4.638 2,565,380 1.043 21.123 5.389 2,519,042 1.815 29.611 5.072
Fort Bend 7,948,707 5.493 61.357 15.746 8,382,481 5.834 64.235 18.171 7,994,337 4.662 62.013 11.965
Galveston 5,816,257 4.117 48.031 11.762 5,941,357 4.218 51.160 13.253 5,850,101 3.89 47.37 8.696
Harris 96,544,278 78.159 870.197 204.910 104,118,424 81.555 936.121 241.000 97,155,857 66.433 792.438 147.484
Liberty 2,524,022 1.539 20.206 5.223 2,369,354 1.532 19.093 5.334 2,529,328 2.291 29.303 4.502
Montgomery 10,096,087 6.379 76.684 20.107 10,079,347 6.510 77.152 21.582 10,141,862 6.173 82.879 16.415
Waller 1,946,771 1.490 19.040 4.188 1,880,278 1.526 19.375 4.433 1,949,623 1.785 24.601 3.901
TOTAL 133,092,936 102.359 1159.447 278.032 141,147,536 106.645 1235.310 322.014 133,868,660 90.708 1115.259 206.739

Table 5-2. Percent Difference between MOVES and MOBILE6 Inventory Results

  % Difference, TDM VMT basis, relative to MOBILE6 % Difference, HPMS VMT basis, relative to MOBILE6
County VMT VOC CO NOx VMT VOC CO NOx
Brazoria -0.4% 15.7% -2.2% 31.6% 1.4% 21.0% 0.0% 47.7%
Chambers -0.4% -47.7% -39.6% -8.6% 1.8% -42.5% -28.7% 6.3%
Fort Bend -0.6% 17.8% -1.1% 31.6% 4.9% 25.1% 3.6% 51.9%
Galveston -0.6% 5.8% 1.4% 35.3% 1.6% 8.4% 8.0% 52.4%
Harris -0.6% 17.7% 9.8% 38.9% 7.2% 22.8% 18.1% 63.4%
Liberty -0.2% -32.8% -31.0% 16.0% -6.3% -33.1% -34.8% 18.5%
Montgomery -0.5% 3.3% -7.5% 22.5% -0.6% 5.5% -6.9% 31.5%
Waller -0.1% -16.5% -22.6% 7.4% -3.6% -14.5% -21.2% 13.6%
TOTAL -0.6% 12.8% 4.0% 34.5% 5.4% 17.6% 10.8% 55.8%

Tables 5-3 and 5-4 present emissions and VMT split by light-duty and heavy duty vehicle classification. Consistent with summaries found in TTI's July 2010 Technical Note, vehicle classes in the MOBILE6 summaries are defined as follows:

Similarly, TTI defined light- and heavy-duty vehicles in MOVES output summaries as follows:

For consistency we have duplicated this classification scheme in the following tables. The reader will immediately note in Table 5-4 the large discrepancy in VMT when comparing heavy duty VMT modeled in MOVES to the heavy duty VMT originally modeled by TTI in MOBILE6. For example, the HD VMT modeled under the TDM-based VMT scenario is between 35 and 40 percent less than that modeled in MOBILE6. This is a result of attempting to directly compare emissions aggregated under MOBILE6 vehicle types (which classify vehicles on a GVWR weight basis) versus emissions aggregated under MOVES source types (which classify vehicles based on their expected mode of operation). In particular, vehicle types HDDV2B through HDDV5 inclusive (along with their gasoline counterparts), considered heavy-duty in MOBILE6, map to MOVES source types 31 (passenger trucks) and 32 (light commercial trucks). These are considered "light-duty" under the TTI classification. Because of this, it is difficult to draw conclusions about emissions when differentiating by vehicle classification, but we include the tables below for reference.

Table 5-3. Summary of VMT and Tons of Emissions, by County and Vehicle Classification, Non-school Ozone Season Weekday

ERG MOVES, TDM-based VMT
County VMT VOC CO NOx
Light Duty Heavy Duty Light Duty Heavy Duty Light Duty Heavy Duty Light Duty Heavy Duty
Brazoria 5,384,087 324,239 3.873 0.360 43.806 2.226 6.511 4.945
Chambers 2,368,948 139,540 0.836 0.113 17.175 0.725 2.636 2.002
Fort Bend 7,486,363 462,344 4.929 0.563 57.827 3.530 8.396 7.349
Galveston 5,490,933 325,324 3.725 0.392 45.727 2.304 6.566 5.196
Harris 91,292,024 5,252,254 71.501 6.658 828.843 41.353 117.144 87.766
Liberty 2,379,054 144,968 1.394 0.145 19.192 1.014 3.119 2.104
Montgomery 9,487,457 608,630 5.720 0.659 72.649 4.035 10.620 9.487
Waller 1,834,222 112,549 1.393 0.096 18.427 0.614 2.593 1.596
TOTAL 125,723,088 7,369,848 93.373 8.986 1103.645 55.802 157.586 120.446
ERG MOVES, HPMS-based VMT
County VMT VOC CO NOx
Light Duty Heavy Duty Light Duty Heavy Duty Light Duty Heavy Duty Light Duty Heavy Duty
Brazoria 5,350,307 460,608 3.922 0.505 43.709 3.342 6.399 6.453
Chambers 2,361,987 203,393 0.881 0.162 19.870 1.253 2.749 2.640
Fort Bend 7,718,045 664,436 5.048 0.786 58.974 5.261 8.483 9.689
Galveston 5,470,464 470,893 3.692 0.525 47.672 3.488 6.474 6.779
Harris 95,863,528 8,254,896 72.015 9.540 870.072 66.049 119.679 121.321
Liberty 2,181,503 187,851 1.347 0.185 17.744 1.349 2.860 2.474
Montgomery 9,280,219 799,128 5.682 0.828 71.543 5.609 10.299 11.283
Waller 1,731,203 149,075 1.397 0.129 18.457 0.918 2.521 1.912
TOTAL 129,957,256 11,190,280 93.986 12.659 1148.040 87.270 159.462 162.552
TTI MOBILE6 Inventory
County VMT VOC CO NOx
Light Duty Heavy Duty Light Duty Heavy Duty Light Duty Heavy Duty Light Duty Heavy Duty
Brazoria 5,188,114 540,396 3.424 0.235 45.400 1.644 3.726 4.978
Chambers 2,302,383 216,659 1.735 0.080 28.854 0.757 2.050 3.022
Fort Bend 7,227,617 766,720 4.303 0.359 59.541 2.472 4.859 7.106
Galveston 5,310,752 539,349 3.633 0.257 45.601 1.770 3.713 4.984
Harris 88,607,611 8,548,246 62.147 4.285 762.826 29.612 64.143 83.341
Liberty 2,289,017 240,311 2.194 0.096 28.581 0.722 2.228 2.275
Montgomery 9,135,188 1,006,674 5.734 0.439 79.721 3.157 6.491 9.924
Waller 1,769,669 179,955 1.718 0.069 24.013 0.589 1.752 2.149
TOTAL 121,830,351 12,038,310 84.888 5.820 1074.537 40.723 88.962 117.779

Table 5-4. Percent Difference between MOVES and MOBILE6 Inventory Results, by Vehicle Classification

% Difference, TDM VMT basis, relative to MOBILE6
County VMT VOC CO NOx
Light Duty Heavy Duty Light Duty Heavy Duty Light Duty Heavy Duty Light Duty Heavy Duty
Brazoria 3.8% -40.0% 13.1% 53.1% -3.5% 35.4% 74.8% -0.7%
Chambers 2.9% -35.6% -51.8% 41.6% -40.5% -4.2% 28.6% -33.7%
Fort Bend 3.6% -39.7% 14.6% 56.9% -2.9% 42.8% 72.8% 3.4%
Galveston 3.4% -39.7% 2.5% 52.5% 0.3% 30.2% 76.8% 4.3%
Harris 3.0% -38.6% 15.1% 55.4% 8.7% 39.7% 82.6% 5.3%
Liberty 3.9% -39.7% -36.5% 51.3% -32.9% 40.5% 40.0% -7.5%
Montgomery 3.9% -39.5% -0.2% 50.0% -8.9% 27.8% 63.6% -4.4%
Waller 3.6% -37.5% -18.9% 39.8% -23.3% 4.2% 48.0% -25.7%
TOTAL 3.2% -38.8% 10.0% 54.4% 2.7% 37.0% 77.1% 2.3%
% Difference, HPMS VMT basis, relative to MOBILE6
County VMT VOC CO NOx
Light Duty Heavy Duty Light Duty Heavy Duty Light Duty Heavy Duty Light Duty Heavy Duty
Brazoria 3.1% -14.8% 14.6% 114.8% -3.7% 103.3% 71.7% 29.6%
Chambers 2.6% -6.1% -49.2% 102.2% -31.1% 65.6% 34.1% -12.6%
Fort Bend 6.8% -13.3% 17.3% 118.9% -1.0% 112.8% 74.6% 36.3%
Galveston 3.0% -12.7% 1.6% 104.4% 4.5% 97.1% 74.4% 36.0%
Harris 8.2% -3.4% 15.9% 122.6% 14.1% 123.0% 86.6% 45.6%
Liberty -4.7% -21.8% -38.6% 92.3% -37.9% 86.8% 28.3% 8.8%
Montgomery 1.6% -20.6% -0.9% 88.7% -10.3% 77.7% 58.7% 13.7%
Waller -2.2% -17.2% -18.7% 86.5% -23.1% 55.9% 43.9% -11.0%
TOTAL 6.7% -7.0% 10.7% 117.5% 6.8% 114.3% 79.2% 38.0%

Tables 5-5 and 5-6 present emissions and VMT split by on-network and off-network process classification. Processes associated with running exhaust and evaporative emissions were classified as on-network, while off-network processes included emissions due to vehicle starts and extended idling. This classification is consistent with that proposed in TTI's July 2010 Technical Note.

Table 5-5. Summary of VMT and Tons of Emissions, by County and Emissions Process Classification, Non-school Ozone Season Weekday

ERG MOVES, TDM-based VMT
County VMT VOC CO NOx
On-Network Off-Network On-Network Off-Network On-Network Off-Network On-Network Off-Network
Brazoria 5,708,326 0 2.655 1.578 33.711 12.321 9.896 1.561
Chambers 2,508,488 0 0.776 0.173 16.787 1.112 4.471 0.167
Fort Bend 7,948,707 0 3.465 2.027 45.518 15.839 13.631 2.114
Galveston 5,816,257 0 2.747 1.370 37.998 10.033 10.371 1.391
Harris 96,544,278 0 51.308 26.850 672.636 197.561 177.997 26.914
Liberty 2,524,022 0 1.153 0.386 17.275 2.931 4.858 0.364
Montgomery 10,096,087 0 4.254 2.125 59.757 16.927 17.963 2.144
Waller 1,946,771 0 0.945 0.544 14.301 4.740 3.720 0.469
TOTAL 133,092,936 0 67.304 35.055 897.982 261.464 242.907 35.124
ERG MOVES, HPMS-based VMT
County VMT VOC CO NOx
On-Network Off-Network On-Network Off-Network On-Network Off-Network On-Network Off-Network
Brazoria 5,810,915 0 2.825 1.602 34.699 12.351 11.231 1.621
Chambers 2,565,380 0 0.863 0.180 20.005 1.118 5.211 0.179
Fort Bend 8,382,481 0 3.765 2.068 48.346 15.889 15.958 2.213
Galveston 5,941,357 0 2.829 1.389 41.105 10.056 11.818 1.435
Harris 104,118,424 0 54.261 27.294 738.071 198.050 213.114 27.886
Liberty 2,369,354 0 1.143 0.389 16.157 2.936 4.959 0.375
Montgomery 10,079,347 0 4.367 2.144 60.201 16.951 19.389 2.193
Waller 1,880,278 0 0.979 0.547 14.631 4.744 3.956 0.477
TOTAL 141,147,536 0 71.032 35.613 973.216 262.094 285.635 36.379
TTI MOBILE6 Inventory
County VMT VOC CO NOx
On-Network Off-Network On-Network Off-Network On-Network Off-Network On-Network Off-Network
Brazoria 5,728,510 0 1.540 2.119 35.645 11.399 8.074 0.630
Chambers 2,519,042 0 0.680 1.135 23.798 5.813 4.752 0.320
Fort Bend 7,994,337 0 2.105 2.557 47.126 14.887 11.194 0.771
Galveston 5,850,101 0 1.705 2.185 35.768 11.602 8.077 0.619
Harris 97,155,857 0 29.493 36.940 601.275 191.163 136.906 10.578
Liberty 2,529,328 0 0.883 1.408 22.528 6.775 4.128 0.374
Montgomery 10,141,862 0 2.615 3.558 62.455 20.424 15.355 1.060
Waller 1,949,623 0 0.637 1.148 19.379 5.222 3.613 0.288
TOTAL 133,868,660 0 39.658 51.050 847.974 267.285 192.099 14.640

Table 5-6. Percent Difference between MOVES and MOBILE6 Inventory Results, by Emissions Process Classification

% Difference, TDM VMT basis, relative to MOBILE6
County VMT VOC CO NOx
On-Network Off-Network On-Network Off-Network On-Network Off-Network On-Network Off-Network
Brazoria -0.4% 0.0% 72.4% -25.5% -5.4% 8.1% 22.6% 147.7%
Chambers -0.4% 0.0% 14.1% -84.7% -29.5% -80.9% -5.9% -47.8%
Fort Bend -0.6% 0.0% 64.6% -20.7% -3.4% 6.4% 21.8% 174.2%
Galveston -0.6% 0.0% 61.1% -37.3% 6.2% -13.5% 28.4% 124.7%
Harris -0.6% 0.0% 74.0% -27.3% 11.9% 3.3% 30.0% 154.4%
Liberty -0.2% 0.0% 30.6% -72.6% -23.3% -56.7% 17.7% -2.6%
Montgomery -0.5% 0.0% 62.7% -40.3% -4.3% -17.1% 17.0% 102.2%
Waller -0.1% 0.0% 48.4% -52.6% -26.2% -9.2% 2.9% 62.8%
TOTAL -0.6% 0.0% 69.7% -31.3% 5.9% -2.2% 26.4% 139.9%
% Difference, HPMS VMT basis, relative to MOBILE6
County VMT VOC CO NOx
On-Network Off-Network On-Network Off-Network On-Network Off-Network On-Network Off-Network
Brazoria 1.4% 0.0% 83.4% -24.4% -2.7% 8.4% 39.1% 157.4%
Chambers 1.8% 0.0% 27.0% -84.2% -15.9% -80.8% 9.7% -44.2%
Fort Bend 4.9% 0.0% 78.9% -19.1% 2.6% 6.7% 42.6% 187.0%
Galveston 1.6% 0.0% 65.9% -36.4% 14.9% -13.3% 46.3% 131.9%
Harris 7.2% 0.0% 84.0% -26.1% 22.8% 3.6% 55.7% 163.6%
Liberty -6.3% 0.0% 29.4% -72.4% -28.3% -56.7% 20.1% 0.2%
Montgomery -0.6% 0.0% 67.0% -39.8% -3.6% -17.0% 26.3% 106.9%
Waller -3.6% 0.0% 53.7% -52.3% -24.5% -9.2% 9.5% 65.7%
TOTAL 5.4% 0.0% 79.1% -30.2% 14.8% -1.9% 48.7% 148.5%

Complete summaries of emissions and VMT output by county for each model run performed, by VMT-basis (TDM or HPMS), drive cycle (default or Kansas City derived), vehicle classification (light- or heavy-duty), emissions process, and process classification (on- or off-network) are presented in Appendix C. Raw model outputs are also available in Appendix A.

5.2 Comparison of MOVES Default Drive Cycle Output to Alternate Drive Cycle Outputs

In performing comparisons of the modeling performed using MOVES default drive cycles to the modeling conducted using the Kansas City drive cycles developed by ERG, we limited our summaries to only those source types affected by the drive cycle changes. These included motorcycles, passenger cars, passenger trucks, and light commercial trucks (source types IDs 11, 21, 31, and 32, respectively).
Table 5-7 presents a comparison of modeled light duty emissions for the combined 8-county Houston-Galveston area. Note that the Kansas City drive cycles produce slightly lower emissions for both VMT bases, in the range of approximately 1-3%. This difference is dominated by emissions from Harris county; in Appendix D, it can be seen that percent differences range from 1-17% on a by-county basis, with emissions from counties with fewer VMT showing the widest variance. It can also be seen that VOC tends to vary less than the other two pollutants modeled.

Table 5-7. Comparison of Eight County Light Duty Emissions for Both Drive Cycles and VMT Bases (Overall tons)

  Default Cycle KC Cycle % Difference
VMT Basis CO NOx VOC CO NOx VOC CO NOx VOC
HPMS 1148.04 159.46 93.99 1129.63 157.46 92.83 -1.60% -1.25% -1.23%
TDM 1103.64 157.59 93.37 1073.96 153.37 91.97 -2.69% -2.67% -1.50%

Table 5-8 presents a comparison of combined light duty emissions by MOVES source type. The largest differences between the modeled drive cycles are seen in motorcycles, which are a relatively small portion of the light-duty fleet. Overall differences across source types and counties range from approximately +1% to -3%. As before, these emissions are dominated by results from Harris county, and other more rural counties exhibit wider variance in emissions between modeled drive cycles, as shown Appendix D.

Table 5-8. Comparison of Eight County Light Duty Emissions for Both Drive Cycles and VMT Bases (Tons, by Source Type)

    Default Cycle KC Cycle % Difference
VMT Basis Source CO NOx VOC CO NOx VOC CO NOx VOC
HPMS Motorcycles 12.62 0.49 2.66 11.74 0.45 2.63 -6.97% -9.07% -1.26%
Passenger Cars 597.44 78.59 57.21 590.05 77.23 56.69 -1.24% -1.73% -0.90%
Passenger Trucks 364.98 48.49 22.60 358.27 47.79 22.19 -1.84% -1.45% -1.81%
Light Commercial
Trucks
173.00 31.90 11.52 169.56 32.00 11.32 -1.99% 0.33% -1.73%
TDM Motorcycles 2.75 0.11 1.70 2.56 0.10 1.70 -6.92% -8.91% -0.44%
Passenger Cars 588.28 78.81 57.55 575.52 76.43 56.91 -2.17% -3.02% -1.11%
Passenger Trucks 346.57 47.11 22.56 335.32 45.64 22.04 -3.25% -3.13% -2.27%
Light Commercial Trucks 166.04 31.55 11.56 160.56 31.20 11.32 -3.30% -1.11% -2.09%

Table 5-9 presents combined light-duty emissions by MOVES road type. Variations in this table are fairly pronounced. Although there is virtually no change in off-network emissions (which is expected, as no drive cycles for that road type was modified), the Kansas City restricted road types (freeways) have approximately 3-8% higher emissions, while unrestricted road types (local roads) have emissions that are about 5-15% lower. These differences are independent from the rural/urban distinction, which is expected, since as described above we did not have enough microtrips in the Kansas City Data to make that distinction in the development of our final drive cycles. The variation also seems to be independent of VMT calculation basis.

Table 5-9. Comparison of Eight County Light Duty Emissions for Both Drive Cycles and VMT Bases (Tons, by Road Type)

    Default Cycle KC Cycle % Difference
VMT Basis Road Type CO NOx VOC CO NOx VOC CO NOx VOC
HPMS Off-Network 254.27 29.35 52.59 254.27 29.35 52.53 0.00% 0.00% -0.13%
Rural Restricted 36.66 4.80 1.18 37.41 4.81 1.17 2.04% 0.32% -0.13%
Rural Unrestricted 99.23 16.50 5.29 84.53 14.18 4.92 -14.82% -14.06% -7.06%
Urban Restricted 378.54 48.43 12.93 406.51 52.47 13.28 7.39% 8.32% 2.67%
Urban Unrestricted 379.33 60.39 22.00 346.90 56.66 20.94 -8.55% -6.17% -4.81%
TDM Off-Network 254.27 29.35 52.53 254.27 29.35 52.46 0.00% 0.00% -0.15%
Rural Restricted 197.29 25.91 6.67 209.24 27.48 6.80 6.06% 6.06% 1.95%
Rural Unrestricted 404.17 66.26 22.81 364.38 60.38 21.59 -9.85% -8.87% -5.34%
Urban Restricted 121.79 15.48 4.15 131.25 16.95 4.27 7.77% 9.46% 2.95%
Urban Unrestricted 126.13 20.58 7.22 114.82 19.21 6.86 -8.97% -6.67% -4.99%

Table 5-10 presents combined light duty emissions by MOVES emission process ID. For CO and NOx, the only difference between modeled drive cycles is attributable to running exhaust and crankcase running exhaust, and is on the order of about 1-4% less, depending on VMT basis. There is no difference at all in start emissions. For VOC, there is also no difference in start emissions, and further, no difference in evaporative emissions either. This is expected, since start emissions and evaporative emissions are both off-network processes, and as such, should be unaffected by changes to on-network drive cycles. However, there is larger variance in both exhaust and refueling emissions, approximately 4-6% less, depending on the VMT basis modeled.

Table 5-10. Comparison of Eight County Light Duty Emissions for Both Drive Cycles and VMT Bases (Tons, by Emission Process ID)

    Default Cycle KC Cycle % Difference
VMT Basis Process ID CO NOx VOC CO NOx VOC CO NOx VOC
HPMS Running Exh 893.63 130.10 29.42 875.22 128.11 28.35 -2.06% -1.54% -3.65%
Start Exh 254.24 29.35 31.09 254.24 29.35 31.09 0.00% 0.00% 0.00%
Evap Permeation     8.04     8.04     0.00%
Evap Fuel Vent     19.83     19.83     0.00%
Evap Fuel Leak     3.55     3.55     0.00%
Crank Run Exh 0.14 0.01 0.39 0.13 0.01 0.37 -1.42% 2.87% -3.59%
Crank Start Exh 0.03 0.00 0.41 0.03 0.00 0.41 0.00% 0.00% 0.00%
Refuel Disp Vap     0.52     0.49     -5.39%
Refuel Spillage     0.73     0.69     -5.42%
TDM Running Exh 849.24 128.23 28.73 819.56 124.01 27.42 -3.50% -3.29% -4.56%
Start Exh 254.24 29.35 31.09 254.24 29.35 31.09 0.00% 0.00% 0.00%
Evap Permeation     8.04     8.04     0.00%
Evap Fuel Vent     19.90     19.90     0.00%
Evap Fuel Leak     3.59     3.59     0.00%
Crank Run Exh 0.13 0.01 0.39 0.13 0.01 0.37 -2.30% 1.55% -4.46%
Crank Start Exh 0.03 0.00 0.41 0.03 0.00 0.41 0.00% 0.00% 0.00%
Refuel Disp Vap     0.51     0.47     -6.25%
Refuel Spillage     0.72     0.67     -6.21%

The information presented in Tables 7 through 10 above is also available on a by-county basis in Appendix D. As shown in these tables, the effects of implementing the drive cycles developed by ERG in MOVES varied considerably depending on which county was being modeled. The drive cycles we developed were based on largely urban driving data as discussed in Section 4, and applying these drive cycles to more rural counties in the Houston-Galveston area (as exhibited by fewer VMT driven in those counties) produced emissions that may not be representative. On the other hand, emissions from Harris County, the most urban of the counties modeled (with the corresponding largest daily VMT modeled), did not vary much at all. We believe that any alternate drive cycles developed and used in MOVES should closely match the type of driving activity for the area being modeled for emissions to be considered representative.


29 All references to the MOBILE6-based TTI inventory in this section are based on TTI's Production of MOVES On-Road Mobile, Link-Based Emissions Estimates and Document Preparation Technical Note, submitted to TCEQ in July 2010, in which TTI assessed the 2005 and 2006 years using both MOVES and MOBILE6. This is the most recently available document from TTI that discusses summaries of their MOBILE6 -based inventory for 2005 and 2006. This document was produced subsequent to TTI's 2005/2006 On-Road Mobile Source, Ozone Episode Modeling Emission Inventories for the HGB Eight-Hour Nonattainment Area, which was the source of the data we based this analysis upon originally.

Updated: 07/06/2011
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Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101