CONGESTICS:Texas Transp Institute report

The 1998 report confirmed Los Angeles (1.57) and Washington DC (1.43) secure in their top two positions in the Road Congestion Index ranking, but Miami (1.34) and Chicago (1.34) edged out San Francisco (now 1.33) for equal third place.

The greenies at STPP managed some statistical finagles that purport to show extra road doesn’t help relieve congestion and put out a press release claiming the TTI as their ally in their war against roads. (See next article.) Houston TX of course is the metro area that has been bucking the national trend over more than a decade and which keeps slipping down the congestion league ladder, though Phoenix has done a similar job in the past four years. Houston dropped another two points this year (to 1.11) and is now about 10% less congested than at the peak in the mid-80s. Houston also happens to have added lane-miles faster than population and traffic, in no small part thanks to the great success of the Harris County Toll Road Authority there. The TTI data in fact show a general tendency for extra roadway to be associated with reduced congestion, an unsurprising conclusion to most. And TTI itself says of the countries cities as a whole: “the data are fairly clear — not enough roadway is being added to stop the growth in road congestion.” (p.xv) They estimate that on average only 60% of the new roadway needed to keep pace with extra traffic was added 1993 to 1996.

Only two out of 70 cities (Houston and Phoenix) added enough total new lane-km to relieve congestion a little. In terms of recent annual deficit in freeway lane-km added versus laneage need to keep congestion from worsening, Altanta is the major slacker. It should be adding 93 more lane-mi annually than it is to keep congestion constant. Next biggest slacker is Indianapolis 81, then Chicago 77, Minneapolis 71, St Louis 69, Orlando 56, Dallas 54, Detroit 51. The Los Angeles area has done rather well recently with big expansions of capacity in Orange Co and a deficit of 30.

1992 to 1996 congestion worsened fastest in Memphis, Indianapolis, Louisville, Brownsville, Orlando, Minneapolis, Salt Lake City and Las Vegas.

The TTI data show that as a group the larger the metro area the worse the congestion but the medium sized cities are facing a faster rate of growth of congestion, perhaps because when congestion gets bad enough demand for roadspace is suppressed — another way of describing latent demand. People make arrangements to avoid having to drive when traffic is worst. Congestion itself exacts its price in time lost and so there is something of a convergence occuring in congestion levels.

Different measures produced by TTI show slightly different rankings. By per capita delay Washington DC is tops at 67 hrs/yr well ahead of =#2s LA and Seattle at 56hrs.

Incident-related delays in Wash DC and other northeastern cities seems much worse than in LA. Wash DC’s delays are 64% incident-caused compared to 54% in LA. New York 64%, Boston 72%, Baltimore 66% and Philly 59% also suffer more from incident delay than from general recurrent delays (due to chronic overloading). I wondered if the gridlike structure of a network helps to accomodate incidents with less disruption than radials plus beltway and the bottolenecks of major tidal river crossings typical of the northeast? Minneapolis which like LA has a grid has incidents contributing to only 48% of its congestion. But TTI tells me that these numbers are largely modeled, not measured by FHWA, and it is more likely to be the generally narrower highways in the northeast, and meaner shoulders. Given that such a large proportion of incidents only close one lane, the same level of incidents with basically 2x2 lanes will close 25% of capacity in say the New York area, whereas in Los Angeles with basically 2x4-lanes most incidents will close down only 12.5% of capacity?

There are 20 cities with congestion costs estimated at over $1 billion — LA $10.8b, NYC $9.8b, Chicago $4.0b, Wash DC $3.7b, San Franc $3.3b, Detroit $3.2b, Houston $2.4b, Boston $2.2b, Altanta $2.1b, Philadelphia $1.8b, Seattle $1.8b, Dallas $1.8b, Miami $1.5b, San Jose $1.3b, St Louis $1.3b, Baltimore $1.2b, San Diego $1.2b, Denver $1.1b, Phoenix $1.0b,

Minneapolis $1.0b.

The 70 cities now included have a total estimated congestion cost of $78b/year. The list is far from complete. Many cities over 500k especially in the south like Greenville SC, Raleigh-Durham NC, Richmond VA, Savannah GA, Charleston GA, Birmingham Al, Little Rock AK etc are not included. The total pop of the 70 cities covered is 123m about 60% of the metropolitan pop of the country (210m). Coverage of the 1m-plus cities is complete but gets thinner with smaller cities. A lot depends, says TTI candidly on which states will help sponsor their studies! Boulder got added, for example, when CDOT gave a grant.

TTI says you can’t really make a good estimate of national congestion costs from their data. My guess is you should add 15% to the $78b for the missing 40% of mostly smaller cities which makes $90b for 1996 so by now it is probably running close to the big round $100b. (Tim Lomax TTI 409 845 9960 t-lomax@tamu.edu http://mobility.tamu.edu)