I-90 is the longest interstate route, stretching 3,085 miles from Seattle to Boston.
I-10 is the longest east-west transcontinental route, running 2,459 miles from Los Angeles to Jacksonville, Fla.
I-5 is the longest north-south transcontinental route: 1,382 miles from San Diego to Blaine, Wash.
Source: U.S. Department of Transportation's latest study
When the last section of Interstate 75 was opened 35 years ago today, federal transportation officials compared the 1,575-mile highway to the pyramids.
Today local officials say I-75 -- a corridor from Miami to the lakes of Michigan -- has helped shaped the region's economy and is a major contributor to cities along its path, such as Chattanooga; Cleveland, Tenn.; and Dalton and Calhoun in Georgia.
"I would be sad to think what we would be without the interstate," Cleveland Mayor Tom Rowland said.
But local towns without access to the most traveled road in Georgia, such as Rossville and LaFayette, still are working to get a connector to the interstate. Officials say they recognize the interstate is a key factor to their economic growth.
"We would be a booming, booming county," said Walker County Sole Commissioner Bebe Heiskell.
On Dec. 21, 1977, local and federal leaders met four miles north of Marietta, Ga., to celebrate the end of the $3.5 billion project, creating what was then the longest border-to-border interstate in the country.
Then-U.S. Transportation Secretary Brock Adams told a crowd of several hundred: "It is hard to imagine sometimes the implications of the interstate system. It is comparable to the pyramids."
The big, smooth highway halved the time it took to drive from the rural regions to Chattanooga along winding roads, locals said.
Ringgold Mayor Joe Barger remembers frequent wrecks around a curved bend on U.S. Highway 41 toward Chattanooga.
Cleveland City Councilman Charles Poe claims to be one of the first people to drive on the incomplete section of interstate from Cleveland to Chattanooga, when he sped a man who'd been shot to Erlanger in a Cadillac-turned-ambulance.
When looking back on the magnitude of the project, Georgia Department of Transportation spokeswoman Jill Goldberg said it's hard to believe the magnitude of such an undertaking.
"The cost today," she said. "I can't imagine it."
Just last year, GDOT finished widening I-75 across Georgia to three lanes in each direction.
When the interstate was paved, some of the road replaced U.S. Highway 41 in Georgia, which was a national north-south route, Dalton Mayor David Pennington said. If Dalton had lost its access to that route, the city wouldn't be the same, he said.
The major corridor is one reason for the carpet industry's past success, because most of the carpet is shipped by truck, Pennington said. He said the hotel industry also has boomed because it's a direct route for families heading south to Disney World and back.
While locals recognize the economic growth from the interstate, Heiskell said it can also be a blessing in disguise not to have a town gutted by the major road project because it destroys the landscape and also brings higher crime to an area.
"[We] keep our rural setting, and a lot of people like that," she said. "It does give you an edge on retail business and industry, but we have some other reasons to offer."