Another consideration about the Mine Ride may be the popularity of the ride - it isn't practical (parts/wear/maintenance-wise or interval-wise) to be running every possible train if the trains will only be less than half-full all the time. The Mine Ride is a great coaster, sure, but it's heyday in the spotlight is over.
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PO!NT OF VIEW - A Different Look at Roller Coasters
http://www.crosswinds.net/~justmayntz/thrills/