By David Shepardson

WASHINGTON, Oct 11 (Reuters) - Drivers using advanced driver assistance systems like Tesla Autopilot or General Motors Super Cruise often treat their vehicles as fully self-driving despite warnings, a new study has found.

The Insurance Institute for Highway Safety (IIHS), an industry funded group that prods automakers to make safer vehicles, said on Tuesday a survey found regular users of Super Cruise, Nissan/Infiniti ProPILOT Assist and Tesla Autopilot "said they were more likely to perform non-driving-related activities like eating or texting while using their partial automation systems than while driving unassisted."

The IIHS study of 600 active users found 53% of Super Cruise, 42% of Autopilot and 12% of ProPILOT Assist owners "said that they were comfortable treating their vehicles as fully self-driving."

About 40% of users of Autopilot and Super Cruise - two systems with lockout features for failing to pay attention - reported systems had at some point switched off while they were driving and would not reactivate.

"The big-picture message here is that the early adopters of these systems still have a poor understanding of the technology’s limits," said IIHS President David Harkey.

The study comes as the National Highway Traffic Safety Administration (NHTSA) is scrutinizing Autopilot crashes.

Since 2016, the NHTSA has opened 37 special investigations involving 18 deaths in crashes involving Tesla vehicles and where systems like Autopilot were suspected of use.

Tesla did not respond to requests for comment. Tesla says Autopilot does not make vehicles autonomous and is intended for use with a fully attentive driver who is prepared to take over.

GM, which in August said owners could use Super Cruise on 400,000 miles (643,740 km) of North American roads and plans to offer Super Cruise on 22 models by the end of 2023, did not immediately comment.

IIHS said advertisements for Super Cruise focus on hands-free capabilities while Autopilot evokes the name used in passenger airplanes and "implies Tesla’s system is more capable than it really is." IIHS in contrast noted ProPILOT Assist "suggests that it’s an assistance feature, rather than a replacement for the driver."

NHTSA and automakers say none of the systems make vehicles autonomous.

Nissan said its name "is clearly communicating ProPILOT Assist as a system to aid the driver, and it requires hands-on operation. The driver maintains control of the vehicle at all times." (Reporting by David Shepardson; Editing by Robert Birsel)