treasure valley road dust study: final report - ResearchGate

4. RESULTS OF TRAKER MEASUREMENTS IN THE TREASURE
VALLEY
The TRAKER measurements conducted as part of the Treasure Valley Road Dust Study
fall into three categories: Street surveys, multiple measurements on a closed loop of roads, and
special experiments. Al measurements were performed either during the summer or winter 2001
field campaigns.
The TRAKER was used to survey several hundreds of miles of streets in Ada and
Canyon Counties to assess the spatial distributions of road dust emissions and gather information
on parameters that affect a particular roadway’s potential for emissions. These data are used to
express emissions factors in terms of measured or modeled parameters such as roadway VMT,
speed, and setting. The results from this portion of the study are used in assembling the
emissions inventories discussed in Section 5.
A set of roads was traversed with the TRAKER on multiple occasions during both winter
and Summer 2001. The roads constituted a closed loop and were chosen to represent a variety of
conditions and road classes. The data from the loop are used to assess temporal fluctuations in
road dust emissions. These include seasonal differences (summer vs. winter) as well as day-today
and week-to-week differences. The loop data are also used to assess the effect of
precipitation on unpaved road emissions.
Two special studies experiments were also performed during the TVRDS. In the winter,
an experiment was coordinated with the Ada County Highway District (ACHD) to assess the
short-term effects of road sanding on dust emissions. During the summer, a similar experiment
tested the short-term benefits of street sweeping.
4.1 TRAKER Data Processing
Processing of data involved a series of steps. First, each TRAKER data point was
assessed for validity; the criteria for the validity of an individual data point were discussed in
Section 3. Note that the right inlet on the TRAKER was not active for a portion of the winter
2001 season. Therefore, for consistency, all data presented in this section arebased on the
TRAKER signal from the left inlet only. Second, each valid measurement was cast in terms of
an emissions potential. The emissions potential is a characteristic of the road and can be thought
of as a measure of the road “dirtiness”. Third, because each TRAKER data point corresponds to
a point in space on the Treasure Valley roadway network, Geographic Information System (GIS)
coverages were used to assign characteristics to the TRAKER measurement. Thus, each data
point was associated with a particular segment of road (link) that has its own set of attributes
such as number of lanes, travel speed, and setting. Fourth, street survey measurements that
associated with a particular road segment were averaged by season (either winter or summer) and
used to infer trends in road dust emissions with respect to the attributes of that road segment.
TRAKER loop measurements were averaged by road segment and sample date.
The TRAKER was used in the TVRDS primarily to estimate PM 10 emissions. However,
consideration of the distribution of road dust particle sizes allows for the calculation of PM 2.5
emissions as well. Details of this procedure are provided in section 4.1.3.
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