Gemini is definitely a big twin track mine ride. Just look at the construction -- steel tubular track on wooden supports, fairly open cars...
Corkscrew is somewhat rough for such a small coaster.
Don't forget that Kennywood DOES know maintenance. At least on wooden coasters -- you don't keep coasters like Jackrabbit and Racer running so well for so long without knowing what you're doing.
I like Steel Phantom, and I'll miss it (it's sad to see a record-breaker go), but it's a testimony for what Arrow did wrong in the early 90's. Rough construction, crude transitions (IMHO at least).
Magnum was a happy mistake, and even that had its share of problems. It's the ultimate mine train ride, though...
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--Greg
http://www.pobox.com/~gregleg/