State Highway 66 is a 196-mile (315 km) state highway

State highway

State highway, state road or state route can refer to one of three related concepts, two of them related to a state or provincial government in a country that is divided into states or provinces :#A...

 in the U.S. state

U.S. state

A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

 of Oklahoma

Oklahoma

Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...

, beginning at U.S. Highway 81 in El Reno

El Reno, Oklahoma

El Reno is a city in Canadian County, Oklahoma, United States, in the central part of the state. A part of the Oklahoma City Metropolitan Statistical Area, El Reno is west of downtown Oklahoma City...

 and ending at U.S. Highway 60 near White Oak

White Oak, Oklahoma

White Oak is an unincorporated community in Craig County, Oklahoma, United States, along State Highway 66 about one mile west of that road's eastern terminus with U.S. Route 60. The community had a post office from October 14, 1898 until October 31, 1957...

. The highway was designated in 1985 as a replacement for the decommissioned US-66. Although most of the highway follows Historic Route 66, the highway follows US-66's final alignment, joining Interstate 44 through Tulsa

Tulsa, Oklahoma

Tulsa is the second-largest city in the state of Oklahoma and 46th-largest city in the United States. With a population of 391,906 as of the 2010 census, it is the principal municipality of the Tulsa Metropolitan Area, a region with 937,478 residents in the MSA and 988,454 in the CSA. Tulsa's...

 and Oklahoma City

Oklahoma City, Oklahoma

Oklahoma City is the capital and the largest city in the state of Oklahoma. The county seat of Oklahoma County, the city ranks 31st among United States cities in population. The city's population, from the 2010 census, was 579,999, with a metro-area population of 1,252,987 . In 2010, the Oklahoma...

, while older versions of the route follow various city streets through both cities.

The highway has retained its importance for most of its length due to its paralleling Interstate 44 which between 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...

 and Oklahoma City (except in the cities of Tulsa and Oklahoma City) is a toll road

Toll road

A toll road is a privately or publicly built road for which a driver pays a toll for use. Structures for which tolls are charged include toll bridges and toll tunnels. Non-toll roads are financed using other sources of revenue, most typically fuel tax or general tax funds...

.

SH-66 currently has one spur route, designated SH-66B.
State Highway 66 begins at Business I-40 in El Reno

El Reno, Oklahoma

El Reno is a city in Canadian County, Oklahoma, United States, in the central part of the state. A part of the Oklahoma City Metropolitan Statistical Area, El Reno is west of downtown Oklahoma City...

 (another old Route 66 segment), concurrent

Concurrency (road)

A concurrency, overlap, or coincidence in a road network is an instance of one physical road bearing two or more different highway, motorway, or other route numbers...

 at this point with US-81.