I’ve heard the argument that cable’s not a viable form of transit because vehicles cannot move independently of each other. Standard transit technologies – the argument goes – are self-propelled and are therefore immune to problems experienced by other transit vehicles on a line.
This argument is only half-true. The first part is true: Yes, in standard configurations all vehicles are self-propelled. The second part is false: Just because all vehicles move independently of one another, does not mean they are not impacted by each other.
Consider, for example, how many times a fully-functioning streetcar, LRV or subway is stuck in place due to the malfunction of a vehicle ahead of it. Because all vehicles share the same right-of-way, they are just as interdependent upon each others’ movement as a cable system. Even PRT would be susceptible to this (if it existed), and independence is one of that technology’s key selling points.
A problem in one part of a transit system will always reverberate throughout the rest of that system, independent or not.
Buses, one could argue, avoid this problem entirely, but their full independence means high operational costs due to the need for a large number of drivers. (Their independence, however, is also questionable due to the mitigating impacts of traffic, stop lights and scheduling.)
The independence argument is a red herring and completely masks three significant advantages to interdependent movement:
- Cheap Automation – As cable systems move interdependently, automation can be accomplished easier and more cost-effectively than complex automation of independent vehicles. You don’t need a driver in each vehicle – human or otherwise.
- Economies of Scale – Rather than build 30 engines to propel 30 vehicles, cable systems build one engine to move 30 vehicles. The economies of scale that occur here are one of the single greatest reasons for cable’s cost-effectiveness.
- Reliable Headways - Ever waited for half an hour for a bus or streetcar only to have four arrive at one time? That’s what happens with independent vehicles. In a cable system, that doesn’t occur. Because vehicles move interdependently, chain-gangs of vehicles (‘bunching’ as it’s called) is a virtual impossibility.
It’s easy to get caught up in terms like “independence” because it sounds like a good thing. But – really and truly -independence is a non-argument.
After all, independence without impact is irrelevant.
