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. The cost estimates come from a review of dozens of systems worldwide. I've spent the last 2.5 years working with this technology and have generated a significant collection of research on the matter and am confident in the numbers. At the same time, any estimate as wide-ranging as $15 - $45 million is admittedly crude and outliers on both ends of the spectrum do occur. (Those outliers, incidentally, often provide fascinating cautionary tales about what not to do with cable.) Like any major transit technology, the cost is incredibly dependent upon local environment, jurisdiction, capacity requirements, technology requirements and political considerations. If, in the future there is interest, one of the things I'd like to add to the site is a cost database of systems worldwide adjusted for inflation. Thanks for your interest, Andrew, and if you have any other questions, feel free to send them my way. Steven.
  3. 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.
  4. 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.
  5. Hey Kevin, I'll go through your points one-by-one: 1. Surge capacity really isn't an issue because no transit system I know of has that built in. You have to evaluate cable in the same way you would evaluate current public transit systems. 2. Breakdowns are a fact of life, and I've never said they wouldn't occur. I've simply said that they would be far less frequent than our existing technology. I also prefer a philosophy of using back-up diesel engines to guide the vehicle back into the station so that the evacuation can occur in station rather than in mid-air. A sound evacuation procedure is absolutely necessary. 3. The SF airport people mover is a Bombardier CX-100, self-propelled AirTrain system. It is not cable propelled.
  6. Hey Kevin, I'll go through your points one-by-one: 1. 15 mph (24 km/hr) is still above the average speed that most light rail travels at. Furthermore, bottom-supported cable liner systems can reach above 25 mph (40 km/hr) which is competitive with the average speeds of all other forms of transit. Speed is largely dependent on station spacing; few transit technologies eclipse the 40 km/hr threshold. 2. Doppelmayr sales literature states up to 10,000 for certain cable liner configurations and 6,000 for certain gondola systems. 3. Just because you have station attendants, doesn't mean the technology is not automated. The benefit of cable automation is the reliability and short wait times that stem from that automation. Station attendants are desirable as they increase security and community presence. 4. Why is it that just because something is for tourism it can't also be used for transit? Trains were originally used to transport tourists and freight and now their all over cities. 5. The weight of an additional vehicle on a cable is negligible compared to the weight of the cable itself. The more vehicles that are put on the line, the less the total per vehicle energy consumption is. You can think of it like marginal energy cost. 6. While cable can hit 6,000 pphpd, it doesn't actually need to. There is no light rail system in North America that has a line with capacity greater than 3,500. 7. I would be interested in learning about these "rube-goldberg corners". Turning corners is not difficult, it simply requires the infrastructure to do it. 8. Station size is, indeed, an issue. The problem stems not from the size of the infrastructure, however. It stems generally from large station design. I've toured incredibly slim profile stations as well as incredibly huge stations. You have to imagine the infrastructure separate from the architecture, they're two totally different things. 9. Do you have any literature on why Six Flags and Paramount got rid of their lines? Who built those originally?
  7. 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.
  8. Hi Vince, We actually conducted a comprehensive study on this matter a few years back. We went through every transit system's scheduling and reporting and calculated what the offered capacity was. So there's no specific source for it except for us. I noticed, however, that those numbers are a bit out of date and adjusted it upwards to "~ 5,000 pphpd" as Calgary's C-Train is now approaching that figure. Should you have any other sources that can shed light on this matter, we'd be happy to look at them and adjust the numbers accordingly. Also, when looking at these numbers remember two things: Firstly, we're talking about offered capacity - as in how much capacity is a city offering at peak. This is not a commentary on what the theoretical maximum capacity of light rail is. Secondly, as we mention in the post, we understand that there are systems (notably San Francisco, Boston and Calgary) where the offered capacity of light rail trunks that exceed that number. The commentary here is meant to shed light on a bizarre aspect of North America's usage of Light Rail; that we spend a lot of money to build a high-performance, high-capacity technology but rarely actually offer (or have need to offer) a similarly high level of capacity. Steven.