There is a famous shortcut on Maui via Hansen Road--you take it if you're driving upcountry (or back to South Maui) and wish to by-pass the Kahului traffic.
There is a way to get air-borne on this road if you time it right. This only works when there are zero cars of ahead of you. What you do is step on the gas and hit the bump in the road at just the right time. Then your car wheels can briefly leave the ground, and your stomach does a little fun flip. This little trick works best with small sports cars.
I've discovered one other bump on the road between Makena and La Perouse Bay, but it's not quite as exciting.