Civil Engineering Reference
In-Depth Information
Table 13.11
Contribution of transportation to emissions of air pollutants in the United States,
1999 (millions of short tons)
Pollutant
Source category
CO
NO
x
VOCs
PM10
Lead
SO
2
Total
Transportation
Total
75.1
14.1
8.5
0.8
0.5
1.3
100.3
Highway vehicle share
49.9
8.6
5.3
0.3
0.02
0.4
64.5
Fuel combustion
5.3
10.0
0.9
1.0
0.5
16.1
33.8
Industrial processes
7.6
0.9
8.0
1.3
3.2
1.5
22.5
Miscellaneous
9.4
0.3
0.7
20.6
0.0
0.01
31.0
Total
97.4
25.3
18.1
23.7
4.2
18.9
187.6
Share of total (percent)
-
-
-
-
-
-
-
All transportation
77.0
56.0
47.0
3.0
12.0
7.0
53.0
Highway vehicles
51.0
34.0
29.0
1.3
0.5
2.1
34.0
Source
Reference [
31
], p 43. Table 2-1
Table
13.11
estimates the share of each of the above air pollutants emitted in the
US in 1999, by four major sources:
Transportation, Fuels Combustion, Industrial
Process, and Miscellaneous
.
The transportation sector accounts for 53 % of the total annual pollutants
including 34 % generated by highway vehicles. The impact of highway vehicles
air
pollutants on the US population, however, is much is greater than 34 %. This is
because most of the US population lives in urban areas where the largest number of
highway vehicles is concentrated.
'
Congestion Impacts on Tail Pipe Emissions
Emissions increase where vehicles spend more time in congestion. It has been
reported that stop-and-go traf
“
c congestion
releases as much as three times the
”
pollution as free-
[
37
].
Vehicle emissions are lowest in moderate speed ranges, when vehicle speeds are
more uniform, and rise at higher speeds.
fl
owing traf
c
Health Risk from Exposure to Air Pollution
Vehicle-related pollutants such as particular matter and ultra
ne particles (soot from
gasoline or diesel), nitrogen oxide, and carbon monoxide are highly concentrated
immediately downwind from major roadways. Their concentration is highest at the
edge of the road and reduces as distance from the roadway increases (Fig.
13.7
).
These pollutants are highly dangerous to the health of those who live within a
risk zone 1,500 ft from the roadway. Figure
13.8
shows example distances where
multiple health effects are found, including adult heart attacks, lung disease, chronic
heart disease, and children asthma and lung development [
37
].
