TEXAS TRANSP INST:LA’s PODI Biggest in America

Texas Transp Institute (TTI) has abandoned its annual Roadway Congestion report in favor of an Annual Mobility Report. Another darned acronym AMR. In place of the gutsy B&W cover of a thousand backed up cars with CONGESTION reverse blocked over them, we’ve got a happy five color title ‘mobility’ (at left below) with not a backed-up car in sight.

Now that’ll make motorists feel better about sitting in stop-&-go traffic. Think positive guys, this slow traffic is now mobility, not congestion. The admen rule.

And in the new AMR, TTI de-emphasizes our favorite old roadway congestion index (based on actual traffic volumes relative to standardized free-flow roadway loadings) to put more emphasis on congestion-increased travel times which it measures with a Travel Rate Index – an index of average peak hour travel times in normal conditions relative to free-flow travel times, the normal conditions excluding non-recurrent sources of congestion such as the jack-knifed tractor trailer across 5 lanes. Instead of being called obscurely a Travel Rate Index this measure should be called plainly the Peak Overload Delay Index (PODI).

How bad’s US congestion? By the PODI measure one fifth of the TTI’s US cities have a PODI of 1.3 or more, meaning that peak travel times are 30% longer because of regular congestion than free flow times. Almost a third of the cities have PODI’s 1.25 or more. By the PODI measure LA is 1.51, Seattle 1.43, San Francisco-Oakland 1.42 and Wash DC 1.41. There follows Chicago 1.37, Miami and Atlanta 1.34, Boston 1.32 with Detroit, San Diego and Las Vegas scoring PODIs of 1.31. (None in the US can get close to Sydney’s truly Olympian PODI of about 3.0 – see TRnl#44 Nov/Dec 99.)

Please note none of the toll road heavy cities such as New York, Orlando or Houston figure on this list of high PODIs.

Incident delays constitute 57% of total delays, 43% is recurrent or regular overloading delays in which the roads simply have more traffic than they can handle in free flow conditions, TTI reports.

1982 to 1997 the amount of uncongested peak period travel has declined from 65% to 36% and travel in most congested conditions has risen from 14% to 36%. The reason? “Not enough transp system improvements” relative to the growth of demand. (xvii)

TTI at last addresses the enviro question about whether roads help relieve congestion and answers plainly: “Overall mobility in urban areas is better if areas attempt to construct additional roadway at a pace similar to that of traffic demand growth...If roadway is not added at a pace similar to the growth in traffic demand, travel time and delay per person increases.”

A correlation coefficient of 0.69 was found between the lane-km construction deficit (the extent to which capacity increase lagged traffic increase) and growth in peak hour delays. The trite enviro/EPA line that extra highway capacity only induces increased demand and does nothing for congestion is plain wrong, TTI finds. In another test a 0.71 correlation is found. (mobility.tamu.edu)