Friday, January 06, 2006

Thoughts on congestion

I've just received the Fall 2005 issue of Access, the newsletter of the University of California Transportation Center. This edition isn't yet online. I was struck by a couple factoids in the article "What We've Learned About Highway Congestion." From the Cal-Berkeley PeMS database, researchers have determined that maximum highway capacity is achieved at about 60 mph, up sharply from the 40-45 mph estimated earlier. Research also shows that only 21% of congestion is due to "excess demand" -- too many vehicles for the design of the roadway; the other 79% of congestion is due to operational failings such as weather, traffic crashes or failure to provide metered ramp access to freeways. This, of course, underlines the priority that should be given to investing in highway operations -- like snow & ice control. Another tidbit: high-occupancy vehicle (HOV) restriction does encourage carpooling, but otherwise it acts perversely to increase congestion. "Analysis of Bay Area data suggests that the effeect of teh combined penalties is larger than the positive carpooling effect. Thus, the likely net result of HOV restrictions in the Bay Area is worsening congestion." Kinda sounds like the situation we face in salt restriction, ostensibly to improve health and reduce heart attacks. Good theory, but the "net result" may be a worsening of public health (see other posts in this blog).


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