14
Jun

2011

Cable Cars Module, Lesson 5: System Capacity & Line Length of Fixed Grip Cable Cars

Post by Steven Dale

For our new readers: Despite the fact that systems like the planned London Thames Cable Car are often officially called “Cable Cars,” they are more often than not Gondolas. This can be confusing to cable transit novices. To make it easier: Cable Cars are supported from below (like cars) and Gondolas are supported from the top (like ski lift gondolas). This is an error of nomenclature, nothing more.

For Cable Cars Lesson 1, click here. For Cable Cars Lesson 2, click here. For Cable Cars Lesson 3, click here. For Cable Cars Lesson 4, click here.

Thus far we’ve discussed Single Loop, Dual Loop and Dual By-Pass Cable Cars. Those three configurations together constitute the overwhelming majority of all fixed grip cable car technologies.

If it helps, let’s draw an analogy between cable cars and Aerial Rapid Transit systems: The fixed grip configurations listed above are rough equivalents to Aerial Trams. They are useful in point-to-point (or three station) situations, are fast and involve only one or two vehicles shuttling back-and-forth either on the same loop or on two separate loops.

To take the analogy one step further, a Dual Loop Cable Car would be analogous to a Funifor.

The system capacity of a Fixed Grip Cable Car is a function of four variables:

  • Vehicle Size
  • System Speed
  • Whether Single Loop or Dual Loop
  • Line Length

Arguably, the most important of these four variables is the fourth. As there is a maximum of just one vehicle traveling in either direction at any given time, the length of a line has dramatic implications. Assuming a conceptual situation where all things were equal, you can imagine the relationship between system capacity and line length as being a direct one where capacity drops as line length increases:

[easychart type=”line” height=”300″ width=”350″ title=”Conceptual Relationship Between Line Length and System Capacity” groupnames=”Fixed Grip Cable Car” valuenames=”Very Short, Short, Medium, Long, Very Long” group1values=”8000, 4000, 2000, 1000, 500″]

(Note: The chart above should not be taken literally, it is merely a conceptual representation of the relationship between line length and system capacity.)

Consider this comparison: The Mexico City Airport Aerotren travels at a speed of 45 km/hr whereas the Venice People Mover travels at a lethargic 29 km/hr. And yet despite this clear speed advantage, the Aerotren only offers capacity of 600 pphpd whereas the Venice system offers capacity of ~3,000 pphpd.

Aside from the speed mentioned above, there are three major differences between the Aerotren and the Venice People Mover:

  • The Venice system is a Dual By-Pass system and the Aerotren is a Single Loop system.
  • The Venice trains hold 200 passengers, almost double that of the Aerotren’s 104.
  • The Venice system is 870 meters long and the Aerotren is just over 3 kilometers long.

But these three differences do not affect system capacity equally.

According to company literature, the Aerotren vehicles can be expanded to a capacity of 156 persons, thereby increasing system capacity to 800 pphpd. That means a 50% increase in vehicle capacity causes just a 33.3% increase in system capacity.

And while we could imagine an alternate universe Aerotren built – like the Venice system – as a Dual By-Pass, that would theoretically only double its capacity up to a maximum of ~1,600 pphpd – around half of that offered by the Venice APM despite operating at a speed that’s 50% faster.

Most of the capacity disparity here is therefore caused by system length.

So remember: If you’re contemplating a Fixed Grip Cable Car, and you want high capacity, you either need a pretty short line or you’re going to have to opt for another technology.



Want more? Purchase Cable Car Confidential: The Essential Guide to Cable Cars, Urban Gondolas & Cable Propelled Transit and start learning about the world's fastest growing transportation technologies.

Want more? Purchase Cable Car Confidential: The Essential Guide to Cable Cars, Urban Gondolas & Cable Propelled Transit and start learning about the world's fastest growing transportation technologies.

Comments

  1. The graphic is just wrong. It is not linear but logarithmic. Eg. if you double the line length capacity is half. If you quadruple line length capacity is one fourth. therefore capacity never drops to zero. Further there are station dwell times. Given its only a point to point application the vehicles of the short system spend more times in stations that the vehicles of the long system. Long cable car do not make sense because the pulling rope will be much heavier than the vehicle including passengers itself.
  2. Agreed, Matthias. Again, as I say in the post, this is purely about demonstrating a conceptual relationship. There would be no way to demonstrate a clear relationship between the two as there are so many other factors (like station dwell times, like you mention). I just think it important for people to realize that the longer the line, the lower the capacity.
  3. I've also changed the graph to correct some of the issues you spotted.
  4. @ "Long cable car do not make sense because the pulling rope will be much heavier than the vehicle including passengers itself." AND "I just think it important for people to realize that the longer the line, the lower the capacity." So it is better you compare capacities with the unit "persons per hour per kilometer (per direction)".
  5. @ "Venice People Mover travels at a lethargic 29 km/hr" Yesterday I was travelling with the Venice People Mover. This velocity does not matter. You can go from the bus station to a shopping centre or to the port of the cruise ships, so you don't need high speed.
  6. I agree with you that high speeds aren't necessary. The point was to demonstrate that speed is no where near as important as line length as it pertains to line capacity.
  7. Speed does not matter. The CTP must be BETTER than other transit systems.