Arizona State Route 989
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State Route 989, also known as SR-989, is an unmarked state highway in Oro Valley, Arizona that is comprised of a one and a half mile stretch of Tangerine Road west of State Route 77.
This route number was initially intended as part of a proposed highway network for the Tucson area (in this case, the Tangerine Highway) that was never implemented. While no signage exists for this highway, the road is fully maintained by the Arizona Department of Transportation, complete with mile markers. SR-989 is the highest numbered route in the Arizona state highway system.
The reason this exists is because a local wash crosses the highway. In the original planning, this came first so that ADOT would be responsible for the bridge over the wash.