Dwell Times

Post by Steven Dale

Image by Steven Dale.

True story:

While I was touring the Caracas Metrocable earlier this year, myself and my guide were joined by an elderly gentleman in our gondola. Via my guide, I asked the man how he felt about the system. Did he like it? Any complaints?

He said he loved it – except for all the time the gondolas spend in the stations.

When I looked back at my records, it appears that the man had a point. During my tour of the system, I recorded end-to-end travel times of apx. 14 minutes. 5 of those minutes were spent in the three intermediary stations, meaning more than a third of the trip is spent in stations. Dwell times were roughly 1.5 minutes at each station.

Dwell times are something the cable industry isn’t adept at handling yet and that needs to change. Based upon conversations I’ve had with cable engineers, the consensus is that dwell times can be reduced down to 20-30 seconds. Given that such dwell times have been observed in large detachable chairlifts around the world, there’s no reason to believe this isn’t true.

But for whatever reason, the industry tends to install systems with station dwell times of a minute or more.

This wasn’t something unique to Caracas, either. I witnessed similar dwell times with both the Medellin and Caracas Metrocables, suggesting this issue isn’t company specific (Poma built the Medellin system, Doppelmayr the Caracas system).

My guess is that dwell times are not something the cable industry has really actively dealt with in the past. After all, most ski lifts are point-to-point installations. Dwell times simply don’t factor into the equation on most ski hills.

Furthermore, in a ski lift situation, you probably would want dwell times of 1-2 minutes. Given all the equipment, gear and clothing skiers require, more time is needed to board and alight – especially when you consider how slow people move in ski boots.

But we’re not talking about ski hills here. We’re talking about transit and most commuters don’t wear ski boots.

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  1. A gondola jam is, if a gondola is at the station, there are problems to shut the doors and the next gondola is arriving at the station. At winter sport ropeways the gondolas arrive at the station, they brake to 0,5 m/s, the doors open, passengers get off, the gondola drives with this slow speed on the rail from the get-off point around to the get-in point, passengers enter the cabin, the doors are still open, the gondola moves to the starting point, no more passengers enter here the cabin, then the doors shut, some seconds later the gondola starts. If you optimize the dwelling time you have to shorten each procedure. The gondola drives with about 2m/s to the stopping place and brakes to 0 m/s, the doors open for 10 seconds, the doors shut, the gondola starts. 2 seconds later ( ! ) the next gondola stops at the stopping place. If you have a problem with the doors (it isn’t seldom at subways or winter sport ropeways) you have a JAM and a BIG PROBLEM. If you have a time reserve, you could solve the problem. And there is no problem with accessibility by handicapped persons. The following gondola could wait at a jam track, of course, but the jamming gondola doesn’t start, the interval to the third (driving through?) gondola decreases,…Like a car jam at a street, the jam moves backwards, you have to stop the whole system. If you stop a driving rope, the rope and the cabins start to swing (could be a problem at re-starting) and the passengers lose time and are perhaps frightened. By all means a stop of the rope must be avoided at urban ropeways ! Mid stations don’t need a bullwheel, what is it used for? Only if the arrival direction has a separated drive and the exit direction too ( it would be better). To start deceleration/acceleration outside a station it is too expensive. Detachable ropeways with one rope can drive only up to a side wind of 65-70 km/h, detachable ropeways with two (hauling or support) cables can drive up to a wind of 100 km/h. You cannot stop an urban transportation system, because “sorry, today is the wind stronger”. So it is better to move gondolas on two ropes and with this systems (3S, Funitel) the towers are very very expensive. But you need two towers with bullwheels to return the de/acceleration ropes. Deceleration/acceleration outside a station is a nice idea, but too expensive. Why a gondola must be faster than a tram? Guys, before I have to copy my whole website here, please TAKE YOUR TIME and read a little bit there: http://www.abcde-institute.org/urban_ropeways_destination_stops.html so we can discuss at the same eye level (don’t be angry about me).
  2. Regarding loops in stations...not to feed the flames here...but check out page 2 of the most recent issue of WIR magazine. http://www.doppelmayrctec.com/uploads/media/WIR_183_Englisch.pdf Here Doppelmayr has designed two loops to handle the mixed chair and gondola traffic on one of their "kombi" or "chondola" lifts. Granted this solution only applies to end stations, and granted as @Rose points out it's more complicated, but I point this out to highlight the switching rail idea is completely possible as @Matt the engineer and @LX are working on. and yes @Steven Dale 2 minutes seems huge...I'm not sure why that's so long but probably has to do with the length of the mid stations versus cabin spacing (they seem like huge stations in the pictures and the spacing is very dense) together with how they've laid out the machinery in the stations versus passenger traffic flow...yes they could have made the load/unload sections shorter and the lengthened the accel/decel sections but they didn't for some reason. I suppose if they wanted to change this they could change the diameter of the v-belt pulleys that are powering the individual wheels that drive the cabins around the track so that some sections will be rolling faster versus how they are now (this could mean less overall cabins too...this is what I mean by "tuned" to how the customer/regional code wants the lift to run).
  3. Matt the Engineer
    [BC] That'll do it. I don't see any reason that can't be done at a middle station. That magazine's a great resource. I'm very impressed by the 3.5 mile long tram with only 3 towers.
  4. [BC] Very nice to see it before it is online published (in the pull-down-menu). You are an insider.
  5. We can read at the magazine "The gondolas have a station transit speed of 0.15 m/s". "2 minutes seems huge". The giondolas drives 18 m in 2 minutes ( 9 m at the arriving platform and 9 m at the exit platform).
  6. [Guenther Ecker] you're right!...18m at 0.15 m/s will do it. Nice job. I'm more used to gondolas traveling at 0.3 m/s in stations which is as fast as I think I'd ever want them to go while loading/unloading. And yet the cabins have to travel that distance one way or another. It's true, and I think [LX] suggested it, (please correct me if I'm crediting the wrong person) it would be nice if the cabin would quickly stop for 20 sec to unload...then advance...stop for 20 sec to load and then get on its way.
  7. i don't believe the issue was ever if 2 loops could be done, but rather, if 2 loops should be done. i think it's still heavily a space and money issue. if the only way to solve dwell times is with that much extra infrastructure the flexibility of gondola technology is severely decreased, most notably in terms of the idea of small footprint stations in cities. as in, it would no longer be able to say "we can go almost anywhere", but rather "we could go almost anywhere ... as long as you have X by Y amount of space" now, as an end station, the diagram makes the design look pretty slim, small, and not too cumbersome, but stretch that out to a straight line, and suddenly you have to pick between giant station with short dwell or little station with long commute times... either way i don't think it will sell in NA/Euro markets, which would bring us all right back to the same problem, but after significant amounts spent in R&D.
  8. [BC] What is the fastest deceleration [- m/s²] and the fastest acceleration [ m/s² ] gondolas drive at a station?
  9. [Rose] One advantage of gondola transit is, that you can take it as a transportation system in cities of developing countries with not enough space for trams or buses, and in this case you have not enough space for large gondola stations. If you have to integrate the stations into an existing town structure at traffic junctions/road crossings, you haven't much space, too. Not even the station is above the cars on the first floor (townscape problem). You find space for tracks for Urban Ropeways only at the side of roads, but they should not drive above the rooftops (rescuing problems). In town you must have small stations, especially the stations are midstations !
  10. [Guenther Ecker ] I'm not sure about other countries but the Canadian code (CSA Z98-07) says that "The rate of the carrier’s acceleration to and deceleration from the design haul rope speed shall not exceed 2.4 m/s2 under **the most adverse braking conditions**" (emphasis mine). General accel/decel is done more gradually over 8-15m long sections depending on the size of the carriers/terminal and is based more on passenger comfort...and I bet in the transit field there are codes that govern this too since riders are often standing or sitting without seat belts. Does anyone know what other standards may be in force here?
  11. guenther, why are you telling me what i already said?
  12. @GE "Mid stations don’t need a bullwheel, what is it used for?" Midstations very often join two gondola ropeway turnarounds endwise coupled by a conveyor. This is due to inherent limitations of rope length variation due to load and temperature changes and rope stretch over time - "tensioning". It is true however that if the overall distance of the system isn't extremely long then the bullwheels can be eliminated and the station can decouple cabins simply through accel/decel conveyors only.