The following was taken from an IBMWR posting by Frank Glamser:
The original Route 66 number was assigned in 1926 as the highway from
Chicago to Los Angeles. It connected small towns all along the way
providing for economic development. The road was fully paved by 1938.
The road was featured in John Steinbeck’s Grapes of Wrath which came out
in 1939. By 1970 all segments of Route 66 had been bypassed by modern
four-lane highways, and in many cases the old road bed was used for the
new roads. Route 66 was officially decommissioned in 1984 and interest
in its history waned. The road was a major factor in the development of
motels, cabins, camp grounds, and purpose built service stations. You
can find a brief history at <http://www.national66.org/66hstry.html>. In
recent years there has been a resurgence in interest in the history and
legacy of the road. States have designated surviving sections as Old 66
or Historic 66. In Arizona it is the later.