Monday, September 21, 2009

Why the Catenary Talk?

After overriding the Mayor's veto, URS is going to look at how to bring the streetcar to the city. One of the issues, how to power them, will be fun to consider. Though the question asked in the article seems wrong:
"Do you want to be one of the last streetcars with a catenary system, or the first with a new system - that's the dilemma," Nadolny said.
What streetcar actually needs catenary? Simple trolley wire will do. Some interurban lines could run up to 90mph on trolleywire. I don't see why we have to always over-engineer these things. If you want to ugly things up, go ahead and build catenary. Perhaps that is the goal since the idea of wireless streetcars is all the rage.

10 comments:

Patrick said...

I'm confused. What's the difference between catenary and trolley wire? Wikipedia seems to think they're the same thing: http://en.wikipedia.org/wiki/Overhead_lines

crzwdjk said...

Catenary has two (or more) wires: a contact wire that is level, and a support wire that droops between the supports. The contact wire is suspended from the support wire by means of suspenders that are much more frequent than the support poles. Trolley wire has just one wire, which means that it tends to sag more, thus requiring either more support poles, or more tolerance for sag (or, often, both). Usually, trolley wire is used for low speed and street running sections, including in places like yards on electrified mainline railroads.

Winston said...

I did some looking at the route and honestly I don't see where using direct suspension of the trolley wire instead of catneary would save money or be more aesthetically pleasing. The reason is that you need much more frequent supports for direct suspension than for catenary. If you're in an urban area with buildings right against the street then it's pretty easy to just attach brackets to those buildings and support your trolley wire with wires suspended across the street. However, if you don't have buildings adjacent to the street then direct suspension means lots and lots of poles - about 3 times as many as you need for catenary suspension.
Downtown Charlote is not urban in the sense of having buildings built up to the street. I count a total of 4 blocks out of the 16 blocks of trade street where direct suspension MIGHT save money and would reduce aesthetic impact. On the other blocks catenary is the least intrusive and least expensive way to go.
The other reason why catenary is the best choice for most of this route is that outside the 3 mile segment between the university and the hospital it runs along a 4 lane suburban arterial with a 35 mph speed limit which is at the edge of what you can do with direct suspension with reasonable maintenance costs.
As for wireless technologies, I guess you could use batteries downtown, but why? They would cost more in the end and downtown is suburban enough that wires wouldn't be that big of a deal in that context. There is, of course the option of running the trains off of an on-board diesel engine, but that probably isn't what they're thinking of when they say cutting edge.
As a side note, the folks in Charlotte DO use some direct suspension trolley wire in their LYNX light rail system in a couple of places where they deemed it appropriate, so it isn't like they have standards saying that thou shalt use catenary everywhere. In fact, I suspect the journalist asked someone what the wires the trains got their power from were called and was told catenary and is using this term generically for overhead wires and not to specify a wire suspension system.

Jon said...

just stick with overhead electric wires like everyone else, i could careless whether its catenary or trolley wire. if its going to run on tracks (and therefore be confined to a route anyway) theres no point in off-wire capabilities. diesel/CNG/hybrid powered trolley? just stick with a bus then.

i'm always concerned when people start building part of some infrastructure in anticipation of it being finished in the future. change always happens and many times you end up with unused infrastructure. charlotte started building the tracks for a regular modern streetcar, why now try to reinvent the wheel?

no worries about visual clutter, as its been said, downtown charlotte is already suburban. theres almost no buildings downtown built before 1980, so theres no need to consider historic fabric.

Matt Fisher said...

Yes. Why the f*** about this s***? Just stay with the wire. I can't stomach why we would continue to let them get away with the lie that overhead wires cause "visual pollution".

W. K. Lis said...

Bombardier has a PRIMOVE system for light rail and streetcars that "presents an entirely new prospect, particularly for trams operating in historic city centers. Thanks to this technology cityscapes will no longer be disrupted by overhead lines. It allows catenary-free operation of FLEXITY trams in all surroundings including underground. One of its outstanding features is the safe and contactless power transfer. The electric supply components are completely hidden under the vehicle and beneath the track, thus ensuring operation in all weather conditions."

clever-title said...

I'm not positive, but I think that newer LRVs can't use trolley wire. In Newark, they installed pantographs on the old PCC streetcars just before they were replaced to use the catenary strung for newer LRVs.
http://world.nycsubway.org/us/newark/

There's an engineering argument for 3rd rail systems in place of overhead wire, in that there is far less power loss, and no possibility of weather and trucks breaking it. The problem is that it is much more expensive to build a safe system (one that powers segments only when they are covered by the cars)

crzwdjk said...

clever-title: the outer parts of the SF Muni network definitely use trolley wire and are actually compatible with both trolley pole and pantograph. I suspect that in Newark, they figured that if they were going to upgrade the wire to clear pantographs, they might as well install catenary, and not even bother to support trolley pole operation. And they needed to upgrade the overhead anyway to support the much bigger, more powerful, and air conditioned LRVs.

Jon said...

the places that usually bitch about 'visual pollution' are almost always full of strip malls and abundant surface parking.

Jon said...

fellow Streetsblog.net network blog posting of interest on this topic...

GGW: Powering the streetcars, part 2: From web to thread
http://greatergreaterwashington.org/post.cgi?id=3586