treasure valley road dust study: final report - ResearchGate

5.3.3 Comparisons of Road dust emissions with prior work and silt loading
Table 5-15 shows an inter-comparison of paved road dust emissions estimation methods.
In addition to the TRAKER method, four silt loading methods also appear in the table, two from
the current study, and two that are based on previous work performed by SAI (1997). The
emissions estimates using silt loading from the current study are labeled TVRDS SL1 and
TVRDS SL2. In calculating TVRDS SL1 emissions, the silt loadings reported in Table 3-7 are
used for arterial, collector, and local roads. Since road vacuuming was not performed on
freeways, no on-site silt loading data were available for interstates. The EPA AP-42 suggested
default value of 0.02 g/m 2 was used for interstates. Equation 3-3 was used to calculate the
emissions factors for the different road types based on the silt loading values. Actual emissions
were calculated by applying VMT data from the year 2000 Traffic Demand Model results. The
TVRDS SL2 method differs from the TVRDS SL1 method only in the value used for silt
loadings on freeways. In TVRDS SL2, freeway silt loadings are assumed to be the same as for
arterials, 1.9 g/m 2 for winter conditions and 0.5 g/m 2 for the remainder of the year (non-winter).
The use of these silt loadings in place of the default AP-42 values is probably more realistic
since based on TRAKER measurements, it was observed that emissions factors from freeways
were similar to those from arterial roads (see Table 5-5, bottom four entries).
SAI (1997) prepared an emissions inventory for paved and unpaved roads using the silt
loading method. The results of that inventory appear in Table 5-15. Since the inventory was
assembled in 1997, year 2000 traffic information was not available and SAI had to project future
VMT. The entry in Table 5-15 entitled “SAI 2000 Equivalent” uses the same silt loading values
that SAI used in the original emissions inventory. However, actual year 2000 Traffic Demand
Model results were used to estimate vkt.
Table 5-15. Inter-comparison of emissions inventory methods for average winter day and average annual
paved road dust emissions for the year 2000 in the Treasure Valley.
Inventory Method
Average Winter Day Paved Road
Emissions (metric tons/day)
Average Day emissions on
annual basis (metric tons/day)
TVRDS TRAKER 81.2 62.0
TVRDS SL1 (Interstates SL=0.02 g/m 2 ) 58.1 31.3
TVRDS SL2 (Interstates Winter SL =1.9
g/m 2 , Non-winter SL=0.5 g/m 2 )
75.3 40.6
SAI (1995) 32.2 28.1
SAI 2000 Equivalent With Year 2000
TDM Data
35.4 31.2
TVRDS TRAKER = current study using TRAKER
TVRDS SL1 = current study using local silt data with assumption that interstate silt loading is equal to default EPA value of 0.02 g/m 2
TVRDS SL2 = current study using local silt data with assumption that interstate silt loading is same as for arterials with a value of 1.9 g/m 2 for
winter and 0.5 g/m 2 for non-winter days
SAI (1995) = emissions reported in SAI emissions inventory
SAI-2000 Equivalent = Uses same silt loading assumptions as SAI inventory, but actual Traffic Demand Model network for the year 2000 instead
of projection.
For average winter day, paved road dust emissions using the TRAKER method are 2.3
times those from the SAI 2000 Equivalent method (81.2 vs. 35.4 metric tons per day). The
TRAKER method gives 1.4 times higher emissions compared to the AP-42 method using on-site
silt loadings (TVRDS SL1). However, using the more realistic silt loadings for interstates
(TVRDS SL2), the TRAKER-based emissions of 81.2 tons per day and the AP-42-based
emissions of 76.3 tons per day only differ by 8%.
5-16