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A Hybrid Funicular, Image by Steven Dale

This is Part 3 of a 3 Part series on the Innsbruck Hungerburgbahn. Part 1 can be found here and Part 2 can be found here.

The Hungerburgbahn is what is known in the industry as a Hybrid Funicular. It is a unique and rather new technology that defies categorization and is bound to confuse. Even the simple act of calling it a “Funicular” is mistaken because it is only a Funicular in the strictest sense of the term for a disproportionately short part of its journey.

Hybrids are more mutt than purebred and that’s what makes them so special; they’ve got a good mix of genes from a large pool of possibilities. Hybrids are literally cross-breeds between three cable families: Cable Cars, Funiculars and Gondolas. It’s this cross-breeding that allows Hybrids to do things no other traditional or cable transit technology can.

Consider the Hungerburgbahn’s route: A vehicle begins in an Open Air Yet Underground (OAYU) station in downtown Innsbruck. The vehicle then journeys through a single tunnel and then darts quickly up to street level. It then gently ascends to a slim-profile station a couple metres above street level. After allowing riders to board and alight, the vehicle banks sharply to the left and crosses a river on an elegant single-purpose bridge. It then plunges below ground, tunneling under a major highway and then pitches back above ground where it starts a dramatic climb up the side of a mountain. It comes to a rest at its third stop in an inclined position at a dramatic station dangling at the edge of a cliff. The vehicle then finishes its climb and comes to a rest at its final destination in a second OAYU station.

A yellow hybrid vehicle makes the trek up hill (look closely in the upper left corner) while a blue hybrid vehicle departs the Löwenhaus Station and ducks underground. Image by Steven Dale

Now here’s the kicker: Despite the myriad of changes in inclination the vehicle goes through, the rider is absolutely unaware of anything. The inclination of the rider never changes, only the vehicle.

To imagine how Hybrids work, picture a car’s chassis, now imagine the same thing but in the shape of a streetcar. Now populate that chassis with 5 separate gondola cabins that are bolted to the inside of the chassis. These gondola cabins are not stationary, however; they are allowed to tilt freely and independently of the chassis which occurs naturally according to gravity. In all but the flattest tracks, therefore, a Hybrid’s chassis will be inclined to a different degree than the passenger compartments attached to the chassis itself.

A yellow hybrid vehicle waits at the Alpenzoo Station. Notice how the individual cabs are inclined separate from the grey chassis. Image by Steven Dale

It sounds complicated, but it isn’t. Much like a carpenter’s plumb-bob, a gondola will always find a natural, level inclination because it’s supported from above. It doesn’t matter if the carpenter is leaning forward or backward, the bob he’s holding will always find the same natural inclination separate from the carpenter, just as a gondola’s inclination is separate from the inclination of the cable that supports it. As there is no friction from below, gravity can do what it does best, and the gondola finds its natural inclination.

Surface vehicles are the exact opposite. Because their support comes from below, they cannot float free. A surface vehicle’s inclination is exactly the same as the road, track or rail it is supported on. This problem is as common to Cable Cars and Funiculars as it is to Buses, Subways and Light Rail. This makes sharp changes in inclination uncomfortable for riders (particularly standees), and technologically difficult for traditional technologies themselves.

That’s why roads, rails and tracks are typically inclined at a maximum 10 percent inclination. But doing this adds large costs to any bridges or tunnels required because the total ascent and descent must be “stretched-out” so that it doesn’t eclipse the 10 percent limit. The greater the total change in elevation, the greater the stretching-out.

This, of course, adds significantly to the amount of infrastructure required which adds additional cost while damaging the street level urban fabric. Furthermore, streetcars, subways, or any other rail-based technology simply cannot ascend a greater than 10 percent inclination due to a lack of traction and this “stretching-out” becomes an absolute prerequisite.

(Note: After additional research, I’ve found that a 10 percent inclination is typically too high for most urban rail systems, though there have been a few examples. The ability of any train to ascend such an inclination is dependent on the power of the motor and the speed of the train prior to its ascent. The descent is even more difficult. Bad weather significantly decreases a rail vehicle’s ability to deal with high gradients.)

A blue hybrid vehicle crossing a river. Image by Steven Dale

(Note: Some rail-based trains have solved the 10 Degree Problem using what is known as a Rack-Railway.)

Hybrids dispense with “stretched-out” bridges and tunnels. Hybrids disregard the 10 Degree Problem and nimbly leapfrog over (or groundhog under) impediments and intersections with ease. That saves money and does not clutter the streetscape with additional infrastructure. It also means that Hybrids could provide the first true fully-dedicated street level right-of-way, something Light Rail has never been able to accomplish.

Contemporary Light Rail systems operate in what are known as semi-dedicated rights-of-way. Mid-block they operate in their own exclusive rights-of-way, but at intersections they must contend with traffic, pedestrians and cyclists like everyone else. These semi-dedicated rights-of-way are meant to be an improvement on simple mixed traffic operations but statistics show little if any improvements because it is in the intersections where most problems occur, not at mid-block.

It’s a “weakest link” kind of problem and the weakest link in any right-of-way is always the intersection. If a right-of-way does not provide a vehicle exclusive access through, above or below the intersection, that right-of-way is virtually useless. This situation is common to semi-dedicated rights-of-way and are little more than a cosmetic frill that steals road space from private automobiles and cyclists. Some cities have experimented with Transit Signal Priority schemes to correct for this problem, but those schemes have yielded questionable results and a dubious track record.

Hybrids therefore present an intriguing possibility: Vehicles could run mid-block at street level in dedicated rights-of-way. This eliminates the cost of tunneling or elevating an entire line while contributing positively to the streetscape. Come the intersection, however, the vehicles could groundhog under or leapfrog over the problem, thereby preserving the fully-dedicated right-of-way.

This would, in turn, also allow the systems to be fully-automated, an impossibility with semi-dedicated rights-of-way. As was demonstrated by the Hungerburbahn, stations could even be located underneath the intersection, an ideal configuration for all.

A hybrid vehicle enters an inclined tunnel. Notice how the roof of the vehicle is still level despite the chassis's inclination. Image by Steven Dale.

The Hungerburgbahn may not be the silver bullet system cable’s waiting for, but it’s Hybrid configuration is a quantum leap forward for Cable Propelled Transit. While they are admittedly rare, they should not be ignored. Cable Hybrids can finally help transit planners realize their goal of a low-cost, fully-automated system that operates at ground level.

For that reason, Hybrids deserve a ton of respect and a whole lot of attention.