the shortest air route is a great circle
Assuming you're driving (and not flying) the shortest route is 86 miles.
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Great Circle Route
The shortest route between two points on the surface of a planet, when routes are limited to the planet's surface, is the arc of the great circle that connects the two points. The shortest route between two points anywhere, without regard to intervening matter or energy preventing the route from being followed, is always the line connecting the two points.
If you mean by the words "direct route" the shortest distance between two places, distances between two places are shortest at the equator, because of the shape of the planet. If you mean which direction should be traveled to minimize distance, the route taken should be as straight a line as possible.
Take I-94 WEST from Milwaukee to I-494 SOUTH at EXIT 249 in Minnesota outside of St. Paul.Take I-494 SOUTH to South St. Paul.
Because that location is the lowest, shortest route between oceans.
straight line
The shortest route is on I-90 W.
We are an aircraft delivery company and have often reviewed the shortest flying route to Hawaii. The shortest direct route between two airports is Monterey, California to Hilo Hawaii at 2012 Nautical Miles. Fred Sorenson Flight Contract Services, Inc.
about 1900 miles