The Lincoln Highway (dedicated in October 1913) was the first road across the United States. In 2009, a sign was placed in New York’s Times Square to mark the beginning of the highway that extends all the way to San Francisco, California.
 
The Lincoln Highway was nicknamed “America’s Main Street” since at least 1919. In 1988, Drake Hokanson published the first edition of his book, The Lincoln Highway: Main Street Across America. “Main Street Across America” is now the Lincoln Highway’s popular nickname, although the highway was almost never called that before the 1988 book.

 
Wikipedia: Lincoln Highway
The Lincoln Highway was the first road across the United States of America.
 
Conceived and promoted by entrepreneur Carl G. Fisher, the Lincoln Highway spanned coast-to-coast from Times Square in New York City to Lincoln Park in San Francisco, originally through 13 states: New York, New Jersey, Pennsylvania, Ohio, Indiana, Illinois, Iowa, Nebraska, Colorado, Wyoming, Utah, Nevada, and California. In 1915, the “Colorado Loop” was removed, and in 1928, a realignment relocated the Lincoln Highway through the northern tip of West Virginia. Thus, there are a total of 14 states, 128 counties, and over 700 cities, towns and villages through which the highway passed at some time in its history.
 
The first officially recorded length of the entire Lincoln Highway in 1913 was 3,389 miles (5,454 km). Over the years, the road was improved and numerous realignments were made, and by 1924 the highway had been shortened to 3,142 miles (5,057 km). Counting the original route and all of the subsequent realignments, there is a grand total of 5,869 miles (9,445 km).
 
Conceived in 1912 and formally dedicated October 31, 1913, the Lincoln Highway was America’s first national memorial to President Abraham Lincoln, predating the 1922 dedication of the Lincoln Memorial in Washington, D.C. by nine years. As the first automobile road across America, the Lincoln Highway brought great prosperity to the hundreds of cities, towns and villages along the way. The Lincoln Highway became affectionately known as “The Main Street Across America.”
       
21 September 1919, New Orleans (LA) States, “Better Roads Demand All Over the World,” pg. 36, col. 2:
...the Lincoln Highway Association has been so successful in promoting on “America’s Main Street.”
 
12 December 1919, Rockford (IL) Republic, pg. 20, col. 3:
CANADA TO HAVE A ROAD
LIKE LINCOLN HIGHWAY
“America’s Main Street” To Be Dupli-
cated in the Dominion.
Ottawa, Canada, Dec. 12.—“America’s main street,” as the Lincoln highway has been dubbed, will soon be duplicated in Canada.
 
Google Books
Diary of a Motor Journey from Chicago to Los Angeles
By Vernon McGill
Los Angeles, CA: Grafton Publishing Corporation
1922
Pg. 18:
Marshalltown, Iowa, Monday, October 10, 1921.
Left Clinton after an early breakfast at the Hotel Lafayette, and continued our journey over the Lincoln Highway which we had followed from Chicago. This highway is well marked and can be followed from the signs without the aid of map or guide book. It is called “America’s Main Street.”
 
Google News Archive
23 April 1923, St. Petersburg (FL) Evening Independent, “Route of La Salle Is Followed by Nation’s Broadway,” pg. 9, col. 2:
If the Lincoln Highway is America’s Main Street, .this is America’s Broadway.
 
Google News Archive
28 January 1925, Providence (RI) News, pg. 8, col. 2:
AMERICA’S “MAIN” STREET
Seven million dollars were spent last year for Lincoln Highway improvements. This makes approximately $60,000,000 invested in the famous transcontinental turnpike since 1913. And this is three times the sum originally estimated by the founders of the Lincoln Highway Association as necessary to complete the 3100 miles of road.
 
This is America’s real “Main Street.” It is expensive, but it is well travelled and is therefore worth the price.
 
30 August 1971, Gettysburg (PA) Times, “Year-Old Keystone Shortway Fails To Attract Economic Growth Predicted By State” by lee Linder (Associate Press Writer), pg. 5, col. 1:
But nothing too much has happened in the past 12 months around what is also known as Interstate 80…“the green tunnel”...the Main Street Across Pennsylvania on the Main Street Across America.
 
OCLC WorldCat record
The Lincoln Highway : main street across America
Author: Drake Hokanson
Publisher: Iowa City : University of Iowa Press, 1988.
Edition/Format:  eBook : Document : State or province government publication : English : 1st ed
     
New York (NY) Times
February 12, 2009, 6:01 pm
A Lincoln Highway Marker in Times Square
By SEWELL CHAN
Traffic in Times Square does not usually conjure the image of a highway.
 
Nevertheless, Times Square is indeed the eastern terminus of the Lincoln Highway, the nation’s first coast-to-coast road, which was formed in 1913, its 3,389 miles stretching from New York City to San Francisco.
(...)
Jerry Peppers, the New York State director of the Lincoln Highway Association, said in a statement:

The Lincoln Highway brings together the “Main Street Across America” and the nation’s most famous intersection — Broadway and 42nd Street. It’s particularly important to mark the eastern terminus of the Lincoln Highway, where it will serve as a reminder to millions of New Yorkers and visitors from all across the globe who pass through here of our nation’s history and the City’s connection with the rest of the country’s early highways.
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WANE.com (Fort Wayne, IN)
Lincoln Highway signs unveiled in FW
Published : Friday, 22 May 2009, 3:37 PM EDT
FORT WAYNE, Ind. (WANE) - Mayor Tom Henry helped unveil one of the new signs marking the 1915 route of the Lincoln Highway through Fort Wayne Thursday.
 
Nearly one hundred years ago, the privately funded highway was the first coast-to-coast route, connecting New York to California, winding through smaller cities and towns in fourteen states. Once called “Main Street Across America,” the route came through Indiana and through Fort Wayne.