Despite the common misconception that cable systems can only travel in straight lines, many CPT systems can in fact turn corners. Cornering is key to creating urban systems because cities aren’t laid out in straight lines.
(Since bottom supported systems operate on rails, turning is much different, and arguably simpler, so this page will only talk about aerial systems.)
Most aerial cable systems can make turns, although it is difficult, or near impossible, for fixed grip technologies such as aerial trams and pulsed gondolas. (Fixed grip systems, particularly pulsed gondolas systems do sometimes make slight turns along specially designed towers.)
TURNING IN STATIONS
At turning stations, cabins are transfered from one cable loop to another. It is this connection of straight loop segments that together form the turn. In the stations, cabins detach from one loop and are automatically carried through to the next. This concept is illustrated on the left, where each cable loop is a blue and stations are orange. The black arrows indicate the direction of the cabins.
The method of moving from one cable loop to another originally involved having two bullwheels per loop, one at each end, which also meant two in each station. (For example, a three-station, one turn system would have two cable loops and four bullwheels.) This set up, as you may imagine, can get rather complicated — twice the mechanics means twice the space needed for each station and twice the parts to buy and fix.
To simplify and slim down corners, the passive deflection bullwheel was invented. This technology is illustrated in Caracas Metrocable. As you can see from the image above, instead of doubling the number of bullwheels at each turn, engineers essentially doubled up the role of a single bullwheel, allowing it to turn two loops at once. Since turns happen in stations, cabins are detached and slowed for boarding and alighting, allowing the cable to pass by the bullwheel without interference.
The Caracas Metrocable and the Teleferico do Alemáo in Rio de Janeiro are both multiple station systems with multiple turning stations. The Ngong Ping Cable Car in Hong Kong also has two turning stations, yet neither of which allow passengers to board or alight.
TURNING WITH TOWERS
Turning towers are interesting because for a “normal” two-direction system the towers can only achieve a very slight turn, but for single directional systems the turning range is huge. This is due to how a cable itself can turn — the cable can only turn on the outside of a circle, so the cabin can only follow the cable in that one direction. To achieve a second direction you essentially need a second “outer” circle path to follow. The image above shows the turn at Squaw Valley — a pulsed gondola (fixed grip) system. A discussion on that system can be found here.
The Rostock Gondola is a circulator system that was built for the BUGA festival in 2003. The image above shows how a unidirectional system can turn without a station, but in this case the example is rather large and unweildy.
A much more recent and totally fascinating system is the Kolmården Wildlife Park Cable Car in Sweden. The cable runs in one direction taking visitors all over the grounds but in the meantime follows a rather unusual path with overlaps and extreme turns. Yet, because the system runs a single cable in one direction, the turns are achieved with very small, low profile towers. In fact, there is only one station.
While uni-directional systems aren’t really practical for commuter use on their own, one way they may work is if two systems were stacked and operated in opposing directions. This could be the basis for a large circulator system.
In the mean time, turns will most likely continue to largely take place at mid-stations. As we’ve already seen the space required for these turns will continue to decrease while the ability for cornering will only improve.
For more information, check out some of the Gondola Project past posts related to corners:
- Grip Module, Lesson 4: Cornering
- The Complexo de Alemão Teleferico opening this year
- The Pace of Innovation
- Ngong Ping Cable Car (two turning stations that don’t allow boarding)
- Caracas Metrocable (two nearly 90 degree turns in stations)
- Kolmarden Wildlife Park Cable (extreme turning towers)
- Cornering Gondolas in Squaw Valley
- The 10 Most Promising Developments & Discoveries in Cable Transit (2011)