Civil Engineering Reference
In-Depth Information
However, the severity of crashes in congested traf
c is lower at lower speeds than at
higher speed when crashes are more likely to result in fatalities.
The economic loss and personal injuries of crashes under congested conditions
result in signi
cant cost to motorists. Cambridge Systematics [
28
] estimated that
reducing congestion in the 166 most serious bottlenecks in the US would prevent
287,200 crashes over a 20 year period, including 1,150 fatalities and 141,000
injuries
—
an average of over 14,000 crashes with 58 fatalities and 7,050 injuries per
year.
13.2.1.6 Air Pollution, Global Warming and Traf
c Congestion
The emissions of carbon dioxide (CO
2
) have been associated with Greenhouse Gas
(GHG) emissions. In 2007, highway travel accounted for almost 80 % of the 28,000
million pounds of CO
2
related to transportation. Roadway traf
c is therefore a
major contributor to GHG.
The relationship between speed and emissions is important from both congestion
and air quality perspectives. Results of a comprehensive modal emission model
(CMEM) developed in 1999, are shown in Fig.
13.5
.
This
—
emission curve (developed using the CCNEM
model) with actual data points. It can be seen that CO
2
emissions are highest at
speeds below 25
gure compares the speed
30 mph; remain stable at speeds between 35 and 70 mph, and
increase when speeds exceed 70
-
75 mph.
-
13.2.1.7 Air Pollution and Health Impacts of Traf
c Congestion
Six Major Pollutants
Traf
c congestion degrades air quality with direct consequences to human health
[
30
]. For this reason congestion mitigation is often cited as part of an air quality and
sustainability improvement strategy [
31
].
The Clean Air Act Amendments (CAAA) of 1970 (Public Law 91-604, 84 Stat.
1676) required the development of
National Ambient Air Quality Standards
(NAAQS)
for six criteria pollutants considered harmful to public health. Harmful
emissions include: carbon monoxide (CO), lead, nitrogen dioxide (NO
2
), ozone,
particulate matter (PM10), and sulfur dioxide (SO
2
)
[
31
].
A brief description of each of these six major pollutants, as reported in [
32
],
follows:
1.
Carbon Monoxide
Carbon Monoxide (CO) enters the blood stream and links to hemoglobin, reducing
delivery of oxygen to the body
'
s organs and tissues. The health threat from lower
levels of CO is most serious for those who suffer from cardiovascular disease.
