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Definition
Definition
The State Highway System (SHS) is any roadway that is owned and/or maintained by ADOT. Several types of roads are included in the SHS. Scroll down to learn more.
Route Types
Route Types
Mainline Routes
Mainline Routes
Signed (i.e. numbered) highways that carry high volumes of traffic across the nation or state. These include high functional class routes, such as Interstates, U.S. Routes, and State Routes. The majority of SHS routes are mainlines.
Examples of mainline routes
Map of the State Highway System.
Special Routes
Special Routes
Special Routes are optional categories that more clearly define the role and function of a route within the State Highway System (source).
Alternate Routes
Signed routes that branch from a parent route, continue along a different alignment, and then reconnect with the parent route several miles away (source). Unlike state business routes (see below), which traverse a short distance through a local business district, alternate routes are longer and can traverse through several towns and cities. Alternate routes have the same name as their parent but include the “A” qualifier, such as State Route 89A.
State Route 89A between Prescott and Flagstaff
Example
An example of an alternate route is State Route 89A (SR 89A) between Prescott and Flagstaff (see map above). Before 1956, the quickest route from Phoenix to Flagstaff was US 89, traveling from Prescott, north to Ash Fork, and then east to Flagstaff. US 89A was designated as a quicker alternative, departing from US 89 in Prescott, traversing through Cottonwood and Sedona, and then reconnecting with US 89 in Flagstaff (source). In 1992, the route was converted to a State Route (source).
Although the construction of I-17 and I-40 mean SR 89A no longer connects with Highway 89 in Flagstaff, ADOT has retained the alternate "A" qualifier.
State Business Loop 40B in Seligman
State Business Routes
Signed routes that are principally within the corporate limits of a city and pass through the city’s business area (source). There are two types of business routes:
Loops connect with the main route at each end of the business area
Spurs terminate in the business area
Business routes retain the same route number as their parent route but include the “B” qualifier. Also, all business routes are signed as State Routes, regardless of whether the parent route is an Interstate or US Route.
Example
State Business Route 40 (SR 40B) in Seligman, located in northern Arizona, is an example of a business loop. It departs from I-40, traverses through the Seligman business district, and then returns to I-40 after a few miles.
Temporary Routes
Signed routes designed for short-term use to complete a gap in a parent route. Temporary routes are used when a permanent alignment for the main route is not possible, such as when a traffic on a main route must be detoured for a long period while the main route is under construction or maintenance. They are also used when the main route alignment must remain flexible (see the example below). Temporary routes have the same name as their parent but include the “X” qualifier.
Example
U.S. Route 191X (US 191X) in eastern Arizona, north of Clifton. The temporary designation allows the Morenci Copper Mine to periodically move the route to accommodate mining operations while still allowing traffic on US 191 to flow through the area.
US Route 191X north of Clifton.
State Spru 266 south of Fort Grant in eastern Arizona
State Spurs
Signed routes that branch from the mainline but terminate at a destination or at another highway. Unlike alternate routes, spurs do not reconnect with the parent route.
Example
State Spur 266 (SS 266) in eastern Arizona, north of I-10, branches from SR 266 and terminates at the Arizona State Prison Complex at Fort Grant.
Other Route Types
Other Route Types
Ramps
Ramps allow traffic to enter or exit from a limited-access highway, such as a mainline. Unlike interchanges that require vehicles to stop, such as at lights or stop signs, ramps allow vehicles to accelerate or decelerate to match the speed of the traffic they are merging into, minimizing the impact on the flow of traffic.
Frontage Roads
Roads that run parallel to a mainline highway and have slower speed limits, allowing easier access to local businesses and residence.
Examples of ramps and frontage roads
Example of an E-ramp on 7th Street where it crosses I-10
Non-Highway Routes
Any routes that are owned by ADOT but are not signed highways (i.e. they do not have an assigned route number). These include local roads and E-ramps.
E-Ramp
An E-ramp is a special type of ramp designation used by ADOT to categorize portions of local roads that are within the ADOT right-of-way and cross an ADOT-owned mainline route.
An example is the portion of 7th Street that crosses over I-10 in central Phoenix. ADOT owns and maintains the half-mile segment of 7th Street that is within the ADOT right-of-way and designates the section as an E-ramp.
Signed Routes Not Owned by ADOT
Signed Routes Not Owned by ADOT
Some local government agencies have signed (i.e. numbered) routes that they own using the same standard highway nomenclature as ADOT. However, since these routes are not owned or maintained by ADOT, they are not part of the State Highway System.
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