I-90
About 3.0 miles. You get on the on-ramp, get up to 35ish, and coast. I don't EOC, but in neutral, it'll hold 70ish. At the end there, it comes up a little bit, then back down to the merger of the highways, overall about 4.5 miles with maybe 15 seconds of accel.
To the north going across the top of the park, there is another road that has a significant drop. However, the end is a blind corner with an immediate stop sign. Too bad!