The Indiana state road numbering scheme is fairly simple. Basically, odd-numbered highways go north and south and
even-numbered ones go east and west. Lower numbers are on the east and north sides and higher numbers are are on the west and south.
In other words, it is very similar to the US Highway numbering scheme.
In addition, three digit routes exist. Most run parallel to their parent route, but a few are perpendicular.
For example, SR 134, SR 140, SR 520, SR 524, and SR 650 run the opposite direction to their parents. The ones where the cardinal
direction is perpendicular from the parent are usually short spurs.
Some are branches off their parent. For example SR 104, SR 105, SR 115, SR 167, SR 352 and SR 930 are children of
SR 4, SR 5, SR 15, SR 67, US 52, and US 30 respectively.
Others never touch their "parent". For example, SR 103, SR 117, SR 128, SR 213, and SR 236 run parallel to, but
never meet their respective parents: SR 3, SR 17, SR 28, SR 13, and US 36. These are the most common. Yet other 3 digit route follow
old routings of their parent. Examples are SR 158, SR 340, and SR 431. And yet another variant are the state road "placeholders" for future
interstate designations. For example SR 265 and SR 469.
Finally, some are children of parent routes that no longer exist. For instance, SR 129, SR 229, and SR 143 are children of routes that
have been truncated, and SR 121, SR 234 and SR 135 are examples of children of routes that do not even exist anymore.
There generally are no state roads and US highways that share the same number. Until recently, US 131 and SR 131 existed on
opposite sides of the state, however. SR 131 has been decommissioned since.
There are a few unexplainable anomolies.
- Old SR 122 did not fit the system at all, but seemed to be numbered to connect to Ohio 122
- SR 47 is posted north-south, but is clearly east-west. It originally was diagonal, however, but why it was not changed to match reality
- SR 75 and SR 79 are/were totally misplaced. It is unknown why this was done. SR 17 is slightly misplaced, but was originally planned to
go further south and east of its current terminus.
- SR 152 doesn't fit, but was apparently a product of the short-lived US 152
As a byproduct of this numbering scheme, several discontinuous sections exist. For example, there are two unconnected sections of SR 1,
three unconnected sections of SR 114, and four unconnected sections of SR 101. If the numbering were random, discontinuous routes
would not make sense.
An interesting phenomena of the numbering is how several US highways fit or almost fit into the state numbering system. Such examples
are US 6, US 31, US 36, US 40, US 41, and US 50.
In summary, it is a very straight forward and logical system.
In addition to the anomolies listed that still apply these issues exist that detract from the fundamental logic of the numbering system.
Recommended Numbering Changes
- Numbering of three digit routes is arbitrary. For example, despite the fact that SR 128 and SR 332 line up, they have different numbers.
SR 227 and part of SR 101 also closely line up, but have different numbers. On the other hand, the discontinuous sections of SR 119, SR 236,
and SR 356 do not even line up.
- Some three digit routes are children of diagonal routes thereby defeating the purpose of the numbering system. For example, SR 167,
SR 267, SR 352, and SR 229. Child routes should be generally be based on grid routes to preserve the benefits of the scheme.
- Despite the care taken to not have state and US routes with the same number, no attempt was made to do the same when the Interstate
highway system was constructed. In particular, the proximity of SR 64 and I-64 in the southern part of the state cause confusion. When
I-69 is extended, SR 69 and I-69 will cause similar confusion.
- The removal of all routes other than Interstate through Indianapolis is questionable, at best. Particularly, the lack of north
and northwest routes is problematic. Further, the poor signage of routes such as US 31, US 36, US 40 around Indianapolis causes
- Decommisionings cause more inconsistencies. For example, the section of SR 37 northeast of Fort Wayne now sits as a useless
anomoly in the system. Ironically, this section was once SR 14; now that number would make much more sense (see
1937 map). It could also be argued that SR 37 northeast of Indianapolis also
makes little sense any more.
Realizing that any route changes are highly unlikely and as a fun exercise, here are some suggestions for numbering improvements anyway.
Some are easier to accomplish than others:
- SR 37 (northeast of Ft. Wayne) becomes SR 14: lines up and SR 37 makes no sense. Also original route number reinstated.
- SR 17 becomes SR 29: SR 29 makes more sense and both roads line up and meet in Logansport
- SR 352 becomes SR 22: original designation makes more sense (see 1931 map).
- US 421 (Michigan City - Reynolds) becomes SR 43: original designation makes more sense/US 421 designation adds no value.
If US highway designation is desired, US 231 makes more sense.
- US 421 (SR 28 south to I-465) becomes SR 29: original designation makes more sense/US 421 designation adds no value
- US 421 truncated to section from I-74 to Madison: much of route is multiplexed anyway
- SR 37 northeast of Indianapolis becomes SR 15: no longer does the SR 37 designation make sense; other numbers more logical
- SR 54 (south of SR 445) becomes SR 43: to free up SR 54 number/ lines up to existing route better
- SR 54 (west of SR 57) becomes SR 154: to free up SR 54 number/lines up with existing SR 154
- SR 60 becomes SR 54: to free up SR 60 number
- SR 63 (expressway)becomes US 41, US 41 becomes SR 55, SR 55 Wingate-Rob Roy becomes SR 228, US 41 existing
SR 63 to Attica becomes SR SR 141
- SR 64 becomes SR 60: to avoid confusion with I-64, SR 64 number disappears
- SR 69 becomes SR 73: frees up SR 69 number, is furthest west road so should have highest number
- SR 37/SR 54/SR 57 (south of Indianapolis) becomes SR 69: to follow the eventual route of I-69. Would prevent future confusion with existing SR 69.
- SR 37 truncated to section from Bloomington to Tell City
- SR 161 becomes SR 57: relatively major route gets a 2 digit number as former SR 57 became SR 69/I-69
- US 231 (Hebron - Montmorencie) becomes SR 53: original route number makes more sense/US 231 designation adds no value
- US 231 (St. John - Hebron) becomes SR 8: original route number makes more sense.
(see 1940 map).
- US 231 truncated to section from Lafayette to Rockport where it is a major route
- SR 75 becomes SR 139: misplaced number; minor route
- SR 121 (south)/SR 229/SR 129 becomes SR 401: misplaced numbers and all closely line up
- SR 135 becomes SR 29: SR 135 is an anomoly - it was originally SR 35 until US 35 came into being in Indiana
(see 1931 map).
- SR 47 becomes SR 34: is now a primarily east-west road
- Elkhart CR 17 whis is part of the NHS becomes SR 17 from M-217 to US 20
- SR 120 truncated to new SR 17
- SR 121 (north) is decommissioned
- SR 340 is decommissioned