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I'm not sure how those sensors work, but if they are like a typical metal detector they should have no problem registering the Roadster's aluminum frame.
I have a feeling that they are correct on the ferrous metals issue. I have not had any problem when riding my older Honda Shadow with its steel frame and other components. But when riding my heavier Vectrix with its all aluminum frame, nickel metal hydride batteries and copper wound motor there are several sensor controlled intersections that will never change.