The IIHS, a safety research arm of the insurance industry, also said there is no evidence that Autopilot or other assisted-driving systems have real-world safety benefits, based on crash data.
"We are able to look at insurance claims data. We have been able to look at vehicles with and without these (systems) and determine there is no reduction in claims as a result of these more advanced systems," said IIHS president David Harkey.
By comparison, there is evidence that automatic emergency braking systems cut rear-end collisions by 50% and cut incidents of a vehicle hitting a pedestrian by 30%, he said.
Tesla and its chief executive, Elon Musk, have said that a Tesla operating with Autopilot engaged is about 10 times safer than the US average and five times safer than a Tesla without the technology enabled.
Federal regulators are investigating nearly 1,000 accidents in which Tesla's Autopilot was in use.
A civil case scheduled to go to trial next week in California will be the latest test of Tesla's strategy of blaming crashes on drivers who fail to heed the EV maker's warnings to pay attention to the road when Autopilot or Full Self Driving technology are engaged.
Tesla did not reply to an email seeking comment.
The IIHS study rated 14 assisted-driving systems from nine automakers against standards it developed.
The US National Highway Traffic Safety Administration has no formal standards governing advanced-driver assistance systems, or ADAS in industry terminology.
"There are no federal regulations, nor is there good consistent guidance," Harkey said. "That was our reason for putting these safeguards together."
Of the systems IIHS tested, only one earned an acceptable rating: The Lexus Teammate with Advanced Drive, offered last year on a small number of Toyota Motor's luxury Lexus LS hybrid sedans.
"Toyota continuously aims to increase vehicle safety," Toyota said in a statement.
"As a part of that effort, Toyota, among other things, considers performance in third-party testing programs like NHTSA’s New Car Assessment Program and IIHS’s Top Safety Pick program.”
GM's Super Cruise and Nissan's "ProPILOT Assist with Navi-link" offered on the 2023-2024 Ariya electric vehicle received "marginal" overall ratings.
"We are evaluating the results from the first-ever Partial Automation Safeguards test and will continue to work with IIHS in all matters related to customer safety," Nissan said.
GM said in a statement that Super Cruise "is meant to serve as an enhancement to the driving experience," not as a safety feature.
Different assisted-driving systems from Tesla, Mercedes-Benz, BMW, Nissan, Ford, GM, Hyundai's Genesis brand and Geely's Volvo Cars brand received "poor" overall ratings, although all achieved "good" scores on certain elements of the IIHS tests, the group said.
"This new IIHS testing methodology does not assess the performance of the driver assistance systems, instead it focuses on safeguards to prevent misuse," Mercedes said in a statement.
"We take the findings of the IIHS partial driving automation safeguard ratings very seriously."
Automakers could boost safety ratings by adopting existing technology for functions such as driver-monitoring or attention warnings that achieved "good" scores, Harkey said.
Tesla and other automakers are improving the capabilities of their systems, the IIHS said.
Tesla revised its Autopilot software following a federal recall agreement, and IIHS will test the updated system, Harkey said.
"We are certainly going to take in the results of these tests as our cars and these systems continue to evolve," BMW spokesman Jay Hanson said on Monday.
BMW now offers in certain US models a more sophisticated driving-assistance system than the one tested by the IIHS.
The Genesis GV80 SUV that launches in the US this spring will the first model in the Hyundai luxury brand with an in-cabin camera to monitor the driver's face and eyes while assisted driving is engaged.
"This enhancement will also be rolling out to future Genesis products in the coming months and years," the company said.
