University of Virginia Library

Assimilation:

As park roads are swallowed up by the street and highway systems
of the cities and states, so too are signs and symbols. In 1953 when
working on the final phases of the Baltimore-Washington Parkway,
I presented a design for green signboards with white lettering to
distinguish the Parkway from the adjacent streets and highways.
The engineers of the Bureau opposed the use of green because it
lacked the contrast of standard black and white signs. We had one
made in our signshop and installed it as an experiment. People
from 3M saw it and offered to make a sample using their new product
called Scotchlite, a reflective signboard material. That was the
beginning of the green background signs you see on the Interstates
today.

The same thing happened with the long map-like arrows and circles
you see at interchanges. Tommy Herr designed the first sign of that
type for the traffic circle on the Virginia side of the Memorial
Bridge. The International Symbols developed for parks met the same
success...you can't keep exclusive rights to a good idea!