A supplemental route is a state secondary road in the U.S.

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 state of Missouri

Missouri

Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...

, designated with letters. Supplemental routes were various roads within the state which the Missouri Department of Transportation

Missouri Department of Transportation

The Missouri Department of Transportation is a state government organization in charge of maintaining public roadways of the U.S. state of Missouri.-External links:*...

 was given in 1952 to maintain in addition to the regular routes. The goal of the secondary highway system was to place state-maintained roads within two miles (3 km) of more than 95% of all farm houses, schools, churches, cemeteries and stores. The four types of roads designated as Routes are:

• Farm to market roads
• Roads to state parks
• Former alignments of U.S. or state highways
• Short routes connecting state highways from other states to routes in Missouri

Supplemental routes make up 19064 miles (30,680.5 km) (59%) of the state highway system.

Highway designations

The more major supplemental routes of the system are assigned single-letter designations (such as "K"). Minor branch routes and farm-to-market roads, which often end at county roads or are former alignments of other highways, are typically assigned two-letter designations consisting of two of the same letter (e.g. "KK"). Additionally, combinations of letters may be used, but always with "A" as the first letter (such as "AD"). The only exception is Route BA found in western St. Louis County

St. Louis County, Missouri

St. Louis County is a county located in the U.S. state of Missouri. Its county seat is Clayton. St. Louis County is part of the St. Louis Metro Area wherein the independent City of St. Louis and its suburbs in St. Louis County, as well as the surrounding counties in both Missouri and Illinois all...

.

The vast majority of the highways in the system are designated with 19 letters of the alphabet. The letters "G", "I", "L", "Q", and "S" are not used due to potential confusion with "6", "1", "1", "O", and "5" respectively.

The letter "R" is reserved for the first letter of supplemental routes which connect with state parks or other recreational facilities. Route AR, a non-recreational route south of Bakersfield

Bakersfield, Missouri

Bakersfield is a village in Ozark County, Missouri, United States. The population was 285 at the 2000 census.-Geography:Bakersfield is located at ....

, is the only exception to this.

These routes rarely run for more than a few miles, though they may cross county lines. At a U.S. Route or interstate, they change letters, for example, in Greene County

Greene County, Missouri

Greene County is a county located in Southwest Missouri. As of 2010, the population was 275,174 making it the fourth most populated county in Missouri. Its county seat is Springfield...

, southbound Route J crosses U.S. Route 60 and becomes Route NN. But when Route MM crosses Route 360, it remains Route MM, only changing into Route B when crossing Interstate 44. The names are also reused, but not near one another. No letter is reused in a county. Route D exists in Greene County, Newton County, St. Louis County, and in several other counties.

Signage

Supplemental routes are signed by black letters on a white background with a black border. Rarely, the shields will be marked with banners such as EAST, WEST, or END. There are no business or bypass routes for the roads; however, five examples exist of spur route

Spur route

A spur route is a short road forming a branch from a longer, more important route . A bypass or beltway is never considered a true spur route as it typically reconnects with the major road...

s: Spur Route N in Cedar County

Cedar County, Missouri

Cedar County is a county located in the U.S. state of Missouri. As of 2000, the population was 13,733. Its county seat is Stockton.- Origin of name :...

, Spur Route C in Gentry County

Gentry County, Missouri

As of the census of 2000, there were 6,861 people, 2,747 households, and 1,884 families residing in the county. The population density was 14 people per square mile . There were 3,214 housing units at an average density of 6 per square mile...

, Spur Route K (into East Lynn) in Cass County

Cass County, Missouri

Cass County is a county located in the U.S. state of Missouri. As of 2010, the population was 99,478. Its county seat is Harrisonville. The county was organized in 1835 as "Van Buren County", renamed in 1848 after Michigan U.S...

, Spur Route AA (to the Sappington Cemetery State Historic Site

Sappington Cemetery State Historic Site

Sappington Cemetery State Historic Site in Saline County, Missouri, is maintained by the Missouri Department of Natural Resources as a state historic site.- See also:* Meredith Miles Marmaduke* Claiborne Fox Jackson...

) in Saline County, and Spur Route Y in Montgomery County

Montgomery County, Missouri

Montgomery County is a county located in the U.S. state of Missouri. It lies in East Central Missouri, approximately halfway between Columbia and St. Louis. As of 2000, the population was 12,136. It was named in honor of Richard Montgomery, an American Revolutionary War general killed in 1775...

.

It is erroneously believed that due to these roads being designated by letters rather than numbers and their existing in more than one county that these roads are county roads, not state highways, with some businesses and residences located on these roads saying their address is "County Road A" for example. This may have also arisen from the signage used prior to the early 1960s, where the letter was painted black against a white background, with the words "STATE ROAD" above the letter and the county name (in all capital letters) below the letter.