Post by Steven Dale
(For those of you not statistically or mathematically inclined, you’ll probably want to skip this post)
PPHPD is an acronym for persons per hour per direction and is a great tool for calculating offered capacity of a transit line. Unfortunately, it’s not a term that has any sort of mainstream usage or understanding and that means it’s easy for us to be confused when we read reports or news articles about our cities’ transit systems.
When we read a news clipping where someone lauds a transit line carrying “40,000 people” (as is common in my hometown of Toronto), we tend to nod our heads and say “hmm . . . yes . . . that’s a lot of people. We should be proud of ourselves.”
But what does 40,000 people really mean . . ? We’ll get back to that in a minute.
PPHPD boils things down to their lowest common denominator. PPHPD defines this: How many total passenger spaces per hour pass a given point on a transit line in a the single peak direction?
In other words, if over the course of one rush hour, a westbound streetcar is scheduled to arrive at a given stop every fifteen minutes; and those streetcars can each carry 100 passengers each, then we know that the PPHPD of that line at that time is 400 (60 minutes / 15 minutes x 100 passengers = 400 PPHPD).
So let’s apply that knowledge, going back to our 40,000 people example:
The 501 Queen Streetcar in Toronto has the distinction of being the world’s longest Streetcar line, it’s also one of North America’s busiest. That should tell you something. At around 30 km long and running 24 hours per day, it carries 40,000 people (on average) per weekday.
Impressive? I guess, unless you look at it from the perspective of PPHPD. If you look at the 501 from the perspective of PPHPD, you find that on any given day, the501 Queen Streetcar only offers around 2,000 PPHPD at peak rush hour. See the difference there? It’s classic bait-and-switch.
40,000 people sounds impressive so that’s the statistic planners and journalists trot out. 2,000 on the other hand, doesn’t just sound common, it sounds inadequate. What politician wouldn’t want to say 40,000 instead of 2,000?
My point in bringing this up is this: Light Rail/Streetcar technology is very expensive to build. It ranges, generally, between $30 – 75 million USD per kilometer. Some instances such as Seattle, have had costs explode over $100 million USD per kilometer. Meanwhile, there is no single Light Rail line in all of North America that provides an offered capacity greater than ~ 5,000 PPHPD.
(For the wonks out there: Yes, I know Boston’s Green Line provides offered capacity of over 9,000 but that’s only in the trunk section of three converging lines.)
Cable, on the other hand, can be built for between $15 – 45 million USD per kilometer and can provide capacity up to 6,000 PPHPD.
How much sense does that make?
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