19
Nov

2009

PPHPD

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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Comments

  1. "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." Steven, what is the source of your cost estimates? Thanks, Andrew
  2. I spent a few years building lifts with Poma. Top speed when I was there was 1200 fpm. That's less than 15 mph. It would take a major change in technology to advance past that. I just went to see what Poma currently is claiming for a gondola - their sales literature only claims 3000 pph. Length is also an issue. We did Skyrail in Australia, at a length of 5 miles. I can go back and look, but I believe that took 2 sets of drive terminals, each drive 500 hp. But Skyrail is for tourism, not for transit, so the cabins are spaced very far apart, and the capacity is around 700 pph. To do his 6000 pph is going to take a lot of horsepower, even in flat terrain. Yes, you can do electrically powered heaters, etc per cabin. But assuming you go with 6 passenger gondolas, you end up with a complete power and heat system for each 6 passengers. That's a lot of maintenance. And they can't really be automated. The current level of technology would require each station be manned, to watch for problems in the accel/decel sections. They are designed for somewhat seasonal use, and if you tried to turn them into 18 hr/day, 365 day/year use, significant design upgrades would be required. Then there is the handicapped access issue. For the occasional handicapped skier, they stop the lift to let them load. That really wouldn't be acceptable in mass transit. As currently designed, gondolas don't stop for loading. To hit the 3000 (not 6000) pph number, you have to have really short headways, and there isn't much slack in the system. So a mis-load in one terminal would likely cut capacity for the entire system. Turning corners is difficult, generally resulting in the addition of a back-to-back terminal, although there have been a few lifts that have a rube-goldberg corner. The towers are pretty small, but the terminals are easily at least as big as a small monorail station. And due to wind etc, the clearance envelope is about double the line to line distance. So no overhead power lines, signs, etc in the area. When these things go down, (and they do occasionally) rescue is an issue. If you have good terrain, and healthy skiers, you can throw a rope over the line and evacuate with a "bosun's chair". What do you do over a freeway? There are some more complicated rescue methods, but generally in a ski area, those are only required for a few areas. Evacuation is a major reason why the Six Flags and former Paramount Parks got rid of most of their gondola rides. Sorry, this just got me ramped up. Gondola's are a good solution to a narrow band of problems, but urban transit isn't one of them.
  3. As far as the latching (detachable technology) - the normal ski lift technology does come off the cable, but there really isn't any surge capacity. As one comes in, another one has to go. I have spent many a light night pushing chairs and cabins when the cadencing system wasn't set up right. You can build in a surge capacity, but if you do, then your station gets bigger, and/or your capacity goes down. If you have never had to guide a platform lift down a crowded midway to perform an evacuation, you probably shouldn't be calling the evacuation issue "overblown". I have been evacuated from or evacuated other people from multiple roller-coasters, other amusement rides, ski lifts, the aforementioned Skyrail in Australia, two different monorails, and I was even on board the SF Airport transit thing when it went down one time. Even at 99.9% reliability, that means you eventually are going to have a breakdown on the line. At the SF airport, another passenger pulled the door release before maintenance even knew we were broke down. So most of the passengers self-evacuated before maintenance arrived. However, there were a couple of older ladies who couldn't make the first big step down out of the car. I picked up my rental car, and was out of the parking garage, and they were still working on getting them into the building.
  4. Hi, I'd like to know where you got your source for this "Meanwhile, there is no single Light Rail line in all of North America that provides an offered capacity greater than 3,500 PPHPD.". Thanks a lot. Have a nice day.