The gradual replacement of distance signs strategy was the way it was done
in Ireland. I believe it was planned to take 6 years but in the event it
took 8
It is a useful way to minimise replacement costs but it does carry some risk
of confusion, unless speed limit signs normally have a units indication
(which they don't in the UK and Ireland). There were reported incidents of
visting motorists in Ireland causing tale-backs because they thought that
the speed limits were in km/h.
In practice I doubt that distance signs would be replaced overnight because
it's probably too big a job but I would recommend that protracted periods of
gradual replacement be avoided if possible.
Phil Hall
I have proposed ways to metricate our highways for while minimizing the
cost
of doing so. The FHWA had two different proposals to metricate highways,
one was change all the signs at once which had the higher cost and the
other
was replace signs with metric ones as they wore out and needed replacing.
This method would cost no more than the normal cost of replacement.
As we know, the latter approach is not the most desirable. My idea was to
use a hybrid where metric speed limit signs would be placed within 10 to
50
m of current signs. After a period of time, the non-metric signs would be
removed. Guide and warning signs would be gradually replaced as they wore
out, perhaps on an accelerated schedule. Mile-based exit number signs
would
be grandfathered for a period of time in certain states as they just
recently converted from consecutive numbering. To put a change in so soon
will only lead to confusion and resentment. While there would be some
overlap for a few years, if people are educated properly and understand
that
there is no turning back, it will work.
Phil
