As a retired U.S. Highway worker, my pal
Kenny got me started on a little history project
about the first coast to coast highway built
in the United States. Hope you enjoy it.
Route 66 gets all the attention as the "Mother Road" of the United States, but the Lincoln Highway was the first paved, marked and through roadway in the country. The eastern terminus began in New York City and the western in San Francisco.
This marker still stands in Lincoln Park,
San Francisco, CA
Motorists used a ferry to transport them across the bay to Oakland, where before them lay 3389 miles (5454 km)
of mostly crushed stone or paved brick, two-lane highway.
Here's the original route, opened in 1913. The east terminus started in Times Square, New York City, then south through Trenton, NJ and Philadelphia, PA, before heading west. All told, the highway passed through 12 U.S. States.
The men who built the
Lincoln Highway used mostly
picks, hand-held shovels
and sledge hammers.
They resurfaced existing roads, 
most of which were nothing more
than dirt or mud.
Then, they built new roadway
to connect all the paths
 together, making one
transcontinental road.
By the time this picture was
taken in 1936, steam shovels
had replaced hand-helds
and the highway itself had
been divided into
many different names 
and designations.  

In 1925, the U.S. government started planning a federal highway system and in 1926, the name Lincoln Highway was replaced by U.S. Route numbers. This laid the foundation for what would become the now-familiar U.S. highway system. This shows the new designations for each section of the Lincoln Highway.
Here are two sections of the highway still in use today. To the left is Wyoming and above near Pittsburgh, PA.
These photos were taken in the 1930s.
  Many miles are abandoned or nearly forgotten. Above in Ohio and left Nebraska. You can see red brick mixed with more modern asphalt.
In 1919, a 29 year old lieutenant colonel participated in a transcontinental military convoy trek from Washington, D.C. to San Francisco, CA. Here they are in Nebraska.
His name was Dwight D. Eisenhower, seen here on the far right.
37 years later in 1956 as the 34th President of the United States, he signed into law the Federal-Aid Highway Act, which began the construction of the highway system we use today. Interstate 80, which crosses the country from New York to San Francisco, very closely follows the route of the old Lincoln Highway.
Thanks to men like Kenny and all those before and since, tens of thousands of miles of concrete roadway connect the United States from coast to coast in all directions.