The Secret Worldwide Transit Cabal

Informed but opinionated commentary and analysis on urban transportation topics from the Secret Worldwide Transit Cabal. Names have been omitted to protect the guilty.

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Monday, May 12, 2003

 
Wendell Cox Is Not Mediocre, But Sometimes, He's Dense -- 8

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"Truth passes through three phases: 1) It is ridiculed. 2) It is violently opposed. 3) It is accepted as self-evident." Albert Schopenhouer. In the United States, rail is currently passing through Phase Two.


From the Cabalmaster:

For Wendell is Dense Installment 6, click here. For Installment 7, click here (Adobe PDF 5.0 files). These are data tables.

Continuing with our remarkable, landmark, groundbreaking analysis of urban transit traffic density, comparing and contrasting with the poor surrogate, “boarding density,” used by the ever-dense Wendell Cox.

(Hey, Wendell’s into shameless self-promotion, so we thought we’d try it, too.)

First, a bit of a recap: “Traffic density,” passenger-miles per mile of route, sounds like a mouthful but simply describes the number of passengers who travel over each mile of route (usually in both directions). Traffic density has to be tied to some unit of time (year, day, or weekday).

“Boarding density,” boardings per mile, describes the number of passengers who enter stations, or board vehicles, along each mile of route.

To summarize the results on the tables above, we’ve prepared the following list of unweighted annual “Traffic Density Averages,” using the major mode categories described previously:

URBAN HRT:

U.S, Canada, Australia, Western Europe: 14.4 million pass-mi per mile of route.
Eastern Europe: 41.5 million.
Asia: 37.2 million.
Former USSR: 48.7 million.
Latin America: 48.6 million.

LRT:

U.S, Canada, Australia, Western Europe: 4 million pass-mi per mile of route.
Asia: 7.4 million.
Latin America: 11.2 million.

STREETCAR:

U.S, Canada, Australia, Western Europe: 2.3 million pass-mi per mile of route.
Eastern Europe: 10.0 million.
Asia: 2.7 million.
Former USSR: 6.7 million.

SUBURBAN:

U.S, Canada, Australia, Western Europe: 2.2 million pass-mi per mile of route.
Asia: 1.6 million.

LARGE CITY SUBURBAN:

Asia: 44.8 million passenger-miles per mile of route.

ICTS:

U.S, Canada, Australia, Western Europe: 1.8 million pass-mi per mile of route.
Asia: 6.9 million.

MONORAIL:

U.S, Canada, Australia, Western Europe: 4.7 million pass-mi per mile of route.
Asia: 1.5 million.

There is a strong correlation between “traffic density” and “boarding density” (r-squared = 0.9). However, one would expect this, because the two are not independent. The two are not independent because “traffic density” equals “boarding density,” multiplied by average travel distance. A high correlation between two variables that are not independent means little.

(Got that, Wendell??)

The problem for U.S. transit planning, which seldom considers traffic density and related issues, is that the correlation between “boarding density” and “average travel distance” is very weak (r-squared = 0.1). In other words, a line with a relatively low boarding density may have a high traffic density, and vice versa. Not taking this into account may lead to serious problems that are expensive to fix.

The strong correlation between “traffic density” and “boarding density,” compared to the weak correlation between “boarding density” and “average travel distance,” is not a paradox. The strong correlation arises because 1.) “traffic density” = “boarding density” times “average travel distance,” and 2.) “boarding density” is a much larger number than “average travel distance.” Wendell may try his best to convince you that the strong correlation is significant, but it isn’t, because the two variables are not independent.






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