States also have systems in how they number
their state highways. While not all states have logical systems, most will
fall into several categories:
Primary Highways: (usually one- and two-digit
numbers)
In a geographical system, the highways are
numbered in a way similar to interstate and US highways. The numbering
starts on one side of the state, and increases as you go across (ie Florida).
With this system, there is also some sort sort of rule where odd numbers
are one direction and even the other direction, but not always.
In a clustering system, highways in the same
area of the state are around the same number. However, the "areas" are
probably arbitrary, and cross-state highways have to, by definition, violate
this system.
Secondary Highways (usually three-digit numbers):
When a secondary highway is numbered with
the parent route system, usually two numbers from the parent route are
used, and then another digit is slapped in front or behind of those two
digits.
Some states also use clustering for secondary
highways.
Secondary highways can also be numbered by
county.
And then there are states which also number
secondary highways geographically.
Other Systems:
Some states do it in a legislative manner.
This can be done a number of ways, either with the legislature asigning
each route a legislative number, or similar method. Sometimes, this is
the reason you will see clusters of numbers.
As with everything, there are exceptions.
It should be noted that not all states differentiate between primary and
secondary highways, and some states seem to have no system at all.
To find out much more detailed info about
numbering in a specific state, try looking at the highways
page for that state.
Other State Highway Notes
Most of the time, a three digit state highway
is just some sort of spur, link, or loop. However, there are MAJOR violations
of this rule. The one that comes to mind immediately is CO 470, which is
freeway for its entire length. This is a case where a three-digit interstate
was proposed, or it existed, but the state took over, and the state highway
took on the number of the three-digit interstate.
A lot of state highways get their number
by being a decommissioned US highway. Decommissioning is what it's called
when AASHTO decides that a certain US highway should no longer exist along
a certian route, so the number is decommissioned, leaving the state to
do what it wants to. Examples of US -> State decommissioning abound in
every state. For example, MN 16, 61, 210, and 371 are all the old routes
of US 16, 61, 210, and 371 in Minnesota.
Arizona, Indiana
and Pennsylvania number most 3-digit routes as spurs off the 2-digit ones
(i.e. 16 -> 116, 216, etc.) PA's 9xx routes are mostly unrelated to 2-digit
routes.
Washington also does
this, but as a prefix: I-82 gives you 821, 3 gives you 304, 305, etc; I-5
gives you all the 500-series numbers in its corridor.This is much better
than WA's old system where Route 5 had about six different branches, all
labeled route 5! I'm not kidding, that road had more than two ends.
Hawaii has sort of a
Washington system going; Maui has roads in the 30's and 300's for example.
Hawaii and Florida have
4-digit roads that follow the 2- and 3-digit roads. You've seen 9336 in
Florida, but there's also some 2000-series routes.
Some states have more numbered highways than
others, and many skip a lot of numbers. This table shows the highest and
lowest route numbers in each state and province. If there is more than
one number in a box, then there could be a letter suffix or secondary highway
system.
