Normally on U.S. interstate highways, the highway keeps a number below 100 (like 75) and bypasses around major cities (or short dead-end branches) are given an extra digit in front (like 375).

I-75 breaks this rule -- in Tampa, Florida, the main I-75 runs to the east of most of Tampa, while 275 runs through Tampa, crosses Tampa Bay and runs through St. Petersburg, and across the bay again before it merges with 75.

The northern end is in Sault Ste. Marie, Michigan, going through Detroit, into Ohio (Toledo, Dayton, Cincinnati), then Kentucky, eastern Tennessee, Georgia (Atlanta), then finally into Florida, where it goes through Tampa, then east across the top end of the Everglades, known as Alligator Alley, into Miami.

Interstate 75 used to go through Tampa and St. Petersburg, but then in the early 1980s, the powers that be in the Florida Department of Transportation decided to build the bypass through eastern Hillsborough County and changed the number on that portion to 275, indicating to traffic bound for Fort Myers or Miami that they should take the shorter route and stay on I-75. However, since the bypass didn't open for several years after the number was changed, motorists were no doubt even more confused in the intervening period.

There used to be a sign on southbound I-275 near the Ashley Drive exit where the edges of an old "75" shield were visible underneath a newer "275," but that sign has since been replaced.

Between Atlanta and Tampa, I-75 is a very boring drive, with nothing but trees and billboards to look at.

I-75 is one of the most heavily traveled interstates, second in cars per mile to I-95.

The northern terminus is Sault Ste. Marie on the north shore of Michigan's Upper Peninsula. South from there, I-75 traverses a bit of the U.P., and crosses the Mackinac Bridge, one of the longest suspension bridges in the world. It bisects the Lower Peninsula of Michigan, sweeping to the east to pass through Detroit, then directly southward for Toledo, Dayton, and Cincinnati in Ohio, and Lexington in Kentucky. It then tacks to the east to hit Knoxville and Chattanooga, Tennessee, then west to Macon and Atlanta, Georgia. From there it is south to the Tampa area and south along Florida's gulf coast until it heads due east for Miami.

Interesting facts:

I-75 crosses the Great Miami River near Dayton five times. 2000 miles away it hits the city of Miami.
There are no exits to residential streets anywhere along I-75.

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