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National
Major Urban Roads See Drop in Peak Hour Congestion
Last year, peak hour congestion on major urban roads in 99 of the 100 largest metro areas, except Baton Rouge, Louisiana, decreased 30 percent -- being 15 to 60 percent lower each hour of every day depending on day and time -- not because of road expansion, but because of some 3 percent fewer vehicle miles traveled (VMT), an unprecedented decline forced by higher gas prices and economic hardships, and a kind of incidental ''transportation demand management,'' writes CEOs for Cities chief economic analyst Joe Cortright in an Infrastructurist guest commentary on Kirkland, Washington-based INRIX' second annual National Traffic Scorecard, built on many billions of real-time travel data sent from nearly a million GPS-equipped cars and trucks.
Inviting readers to imagine ''how many tens or hundreds of billions it would cost to reduce congestion by 30 percent by building new roads,'' the Portland-Oregon Impresa consulting firm economist points out that the nation ''could just as effectively -- and more efficiently -- accomplish the same purpose with other policies, especially variable road pricing.''
Reported earlier by the Federal Highway Administration (WHWA), the 3 percent VMT decline could produce the 30 percent congestion drop, now evidenced by INRIX, because traffic congestion ''is subject to a tipping point -- what economists call non-linearities,'' the Impresa expert explains.
''Add an additional car to a crowded road at rush hour, and traffic slows down a bit, and then the 'carrying capacity' of the road declines,'' he writes. ''Traffic engineers estimate that most roads carry their maximum throughput -- number of vehicles per hour at about 40 miles per hour -- so as traffic slows below that speed, the road actually loses capacity and goes slower and slower, producing a traffic jam.''
The phenomenon ''has an important implication for transportation policy,'' the economist observes. ''Pricing the roads to reduce peak volumes even slightly -- by encouraging those with flexible schedules to take the trip at some other time, go by another mode, or forego the trip altogether -- makes the system work better for everyone else and actually increases its capacity.''
The road pricing technology ''has been implemented around the country through 'fast pass' electronic tolling,'' and its large-scale introduction has had ''a significant effect on congestion in London and Stockholm,'' he adds, concluding, ''If we truly want to have a smart transportation system for the 21st century, we'll see the lessons of the 'tipping point.'''
See the INRIX press release and its National Traffic Scorecard for 2009 and 2008 at www.inrix.com/pressrelease.asp?ID=65 and http://inrix.com/scorecard/. -- Infrastructurist 3/5/2009
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