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| Route information | ||||
Part of  E90 | ||||
| Length | 32 km (20 mi) | |||
| Existed | 1992–present | |||
| Major junctions | ||||
| West end |   D.330 / D.750 near Tepeköy, Konya | |||
| East end |  O-21 near Eminlik, Niğde | |||
| Location | ||||
| Country | Turkey | |||
| Regions | Central Anatolia | |||
| Provinces | Konya, Niğde | |||
| Highway system | ||||
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Otoyol 21A, abbreviated as O-21A, is a 32 km (20 mi) long auxiliary otoyol connecting the D.330 and D.750 to the O-21. The motorway was opened in 1992 as a connecting route to Konya and passes through mostly uninhabited rural land. The O-21A is a part of the E90.
The motorway was deemed too short to receive its own O-XX designation, despite being longer than the O-50, but too long to be designated as an exit; therefore, the route was signed as the O-21A, and is the only otoyol route in Turkey to have an alpha-numeric route designation.