The magazine said its test of Tesla's Navigate on Autopilot feature, which was first introduced last year for highway driving and updated with new options in April, performed worse than human drivers and even created new risks for them. Consumer Reports reviewed one of the autopilot's optional features that allows the car to automatically change lanes on highways. The function, which needs to be enabled by the driver, automatically switches lanes without driver confirmation until it's disabled or Navigate on Autopilot is turned off.
"The feature cut off cars without leaving enough space and even passed other cars in ways that violate state laws," the magazine said Wednesday. "As a result, the driver often had to prevent the system from making poor decisions."
The damning words from a highly respected consumer review magazine could be a problem for the automaker as it looks to mitigate safety concerns about its Autopilot driver assistance system, which was in use during three deadly car accidents in recent years.
One of the company's recent options offered to its autopilot system allows the vehicle to change lanes on its own without confirmation from the driver.
Though the driver can stop the vehicle from changing lanes by moving the turn signal or canceling the change on the car's touchscreen, Consumer Reports found the feature was subpar compared with human drivers.
"This isn't a convenience at all," Jake Fisher, senior director of auto testing at CR, said in the report. "Monitoring the system is much harder than just changing lanes yourself. Using the system is like monitoring a kid behind the wheel for the very first time. As any parent knows, it's far more convenient and less stressful to simply drive yourself."
Fisher said the feature had an issue responding to other cars that were approaching quickly from behind, causing the vehicle to cut off cars driving much faster. Consumer Reports testers also found the feature struggled to merge into traffic, often automatically breaking to create space between the vehicle and the car in front of it, which can be a "rude surprise" to the vehicle behind it, Fisher said.
Tesla told Consumer Reports that "Navigate on Autopilot is based on map data, fleet data, and data from the vehicle's sensors. However, it is the driver's responsibility to remain in control of the car at all times, including safely executing lane changes."
The company also said in an email to CNBC that its customers have driven millions of miles and safely executed millions of automated lane changes under this optional setting.
Navigate on Autopilot is an added function to Tesla's Autopilot system, which partially takes control of the vehicle and controls its speed while keeping it centered in its lane. There have been three deadly crashes in the U.S. while Autopilot was engaged on Tesla vehicles, according to the National Transportation Safety Board.
As worries about consumer safety rise due to these incidents, Tesla introduced two new features earlier this month that are designed to stop drivers from inadvertently switching lanes. The company presented its Lane Departure Avoidance feature, which flashes reminders to the driver to place their hands on the wheel when departing their lane without a turn signal. If a driver who is using Traffic Aware Cruise Control is repeatedly found to not have their hands on the wheel, the car will slow to 15 miles below the speed limit and flash its hazard lights.
The company also introduced Emergency Lane Departure Avoidance, which steers the vehicle back into its lane if the system detects you could be merging into a possible collision.
Clarification: This article was updated to provide more details about Tesla's software update tested by Consumer Reports.