I've seen a guy riding a scooter down the mountains and along the motorway while I'm going to work lately.
I haven't been close enough to see what model it is (he rides a bit faster than I drive), but it looks like one of the Yamaha Burgman range.
My point is, even with his high vis vest flapping in the breeze and standard bodywork, these things handle motorway speeds OK.
If you started with a 250cc version and improved aero a bit, it could handle any legal speeds NSW has to offer and return pretty good MPG while doing it.
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