The third excerpt from Todd Litman’s ‘Congestion Costing Critique’ – an analysis by the executive director of the Victoria Transport Policy Institute of the Urban Mobility Report (UMR).
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Environmental and Safety Impacts
The Urban Mobility Report claims that congestion significantly increases pollution emissions based on a constantly declining speed-emission curve which assumes that any traffic speed increase reduces fuel consumption and emission rates, although most other studies find that these rates increase over about 55 mph (Figure 7).
The UMR assumes that congestion reductions always save energy and reduce emissions although other researchers conclude otherwise (Bigazzi and Figliozzi 2012). Barth and Boriboonsomin (2009) explain, “If moderate congestion brings average speeds down from a free-flow speed over 70 mph to a slower speed of 45 to 55 mph, this moderate congestion can reduce CO2 emissions.”
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If congestion mitigation raises average traffic speed to above about 65 miles per hour, it can increase CO2 emissions. And, of course, speeds above 65 or 70 also make the roadway more dangerous.” .
The Urban Mobility Report ignores this last point, that congestion reductions can increase traffic risks, although it is much discussed by traffic safety researchers (Marchesini and Weijermars 2010).
Crash rates tend to be lowest on moderately congested roads (V/C=0.6), and increase at lower and higher congestion levels, while fatalities decline at high levels of congestion, indicating a tradeoff between congestion and safety (Zhou and Sisiopiku 1997). Per capita traffic deaths tend to increase with per capita vehicle travel, so roadway expansions that induce additional vehicle travel this tends to increase traffic casualties (Luoma and Sivak 2012).
Full report here.
First excerpt here.
Second excerpt here.
