27 years. The first famous "proof of concept" autonomous driving is Navlab (Thorpe, 1990). (Are there any prior projects?)
Navlab 1 was built in 1986 using a Chevrolet panel van.[2] The van had 5 racks of computer hardware, including 3 Sun workstations, video hardware and GPS receiver, and a Warp supercomputer.[2] The vehicle suffered from software limitations and was not fully functional until the late 80s, when it achieved its top speed of 20 mph (32 km/h).[2] https://en.wikipedia.org/wiki/Navlab
https://en.wikipedia.org/wiki/Ernst_Dickmanns
Already driving on the Autobahn in '87: