Environmental Engineering Reference
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60°
70°
80°
80°
70°
2250
60°
2000
1250
1750
1500
750
500
1000
50°
50°
3000
1250
2500
1000
1000
500
1000
40°
500
700
40°
500
500
100
250
100
1500
1250
250
100
250
500
100
30°
1500
100
0
30°
0
100
0
200
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800
Statute miles
FIGURE 12.21
Distribution of mean air-freezing index values in North America. Design freezing index values are cumulative degree-days of air temperatures below
32°F for the coldest year in a 10-year cycle or the average of the 3 coldest years in a 30-year cycle. (From USACE, Pavement criteria for seasonal frost conditions—
Mobilization construction, U.S. Army Corps of Engineers, 1984.)
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