treasure valley road dust study: final report - ResearchGate

Table 5-6. Unpaved Roads in km for urban and rural areas of Ada and Canyon Counties.
County
Setting
Unpaved Roads
in km
Population in
thousands
Km of Unpaved
Road per 1000
people
Ada Rural 26.1 64.8 0.40
Ada Urban 116 201 0.58
Canyon Rural 20.7 51.4 0.40 a
Canyon Urban 33.4 57.9 0.58 a
a Canyon County estimates of unpaved road length per population are based on Ada County data.
Table 5-7. Vehicle Kilometers Traveled on unpaved Roads in rural and urban portions of Canyon County.
Numbers in bold are estimates.
County Urban/Rural Km ADT VKT Ave_Speed mps
Canyon Urban 33.4 120 4,004 11.2
Canyon Rural 20.7 120 2,488 11.2
In addition to the two broad categories, “rural” and “urban”, there were unpaved roads in Canyon
County that were associated with small rural townships. A list of those is provided in Table 5-8.
Data were only available for the Goldengate Highway District which covers the Wilder and
Greenleaf townships. Based on the total km of roads inventoried in the Goldengate townships
(51.3) and the populations of Greanleaf and Wilder (1880), a length of unpaved road per unit
population was calculated to be (82.5 km/ 1880) = 0.044 km/person. This ratio was used to
estimate the lengths of unpaved roads associated with the townships shown in Table 5-8.
Average daily traffic (ADT) was conservatively estimated as 20 vehicles per day.
Table 5-8. Estimates of km of unpaved roads, average daily traffic, and vehicle speeds for small townships in
Canyon County. Numbers in bold are estimates.
Township
1997 Population
Unpaved roads
(km)
Average Daily
Traffic
Vehicle
kilometers
traveled
Speed (m/s)
Wilder 1232 55 20 1083 11.2
Greeanleaf 648 29 20 570 11.2
Notus 380 16 20 334 11.2
Parma 1597 71 20 1404 11.2
Middleton 1851 82 20 1627 11.2
Melba 252 11 20 221 11.2
5.2.3 Accounting for precipitation effects on unpaved road dust emissions
The effect of meteorology on unpaved road emissions was considered in terms of ground
snow cover and precipitation. On days when there was snow cover on the ground, unpaved road
emissions were set to zero. On days when precipitation was observed, the emissions potential for
dry unpaved roads was multiplied by 0.079 to obtain emissions. For days immediately after a day
when precipitation was observed, the dry emissions potential was multiplied by 0.35 in order to
arrive at the emissions potential for that day. This treatment of precipitation followed directly
from the results of the TRAKER loop data that were summarized in Chapter 5. The loop data
showed that when the ground was wet, emissions were 7.9% of their dry value. The day after a
precipitation event, emissions were still only 35% of their dry values. The average year, based on
historical data between 1940 and 2000, contains 13.2 days where snow cover is present. For the
purposes of emissions inventories, it was assumed that all these days occur during the winter.
79.6 days per year contain measurable precipitation while there is no snow cover present on the
ground. On 10.6 days out of the year, both precipitation and snow cover are observed. The
breakdown of the various conditions is shown in Table 5-9.
5-10