Federal auto safety officials today proposed a new rule requiring black boxes -- data recorders that capture the moments before and after a crash -- in all new U.S. cars and trucks. Such recorders already come standard in most new vehicles, but the auto industry opposes a mandate, and the rule will do little to solve a simmering legal battle over who can see what the black boxes know.

The National Highway Traffic Safety Administration says it will require all new U.S. vehicles to have black boxes by Sept. 1, 2014, noting that 96 percent of 2013 models already come with them standard. The new proposal does not change the 15 types of data black boxes should record when it senses a crash.

"By understanding how drivers respond in a crash and whether key safety systems operate properly, NHTSA and automakers can make our vehicles and our roadways even safer," said U.S. Transportation Secretary Ray LaHood. "This proposal will give us the critical insight and information we need to save more lives."

In use since the 1970s, event data recorders were originally installed as part of air bag systems, recording data such as acceleration, speed, braking and bag deployment in the few seconds before and after a wreck. While the data include whether the driver is wearing a seat belt, it doesn't record any other facts about the driver or the car's location, and can only keep a maximum of five seconds of information.

Safety advocates have long contended black boxes could be used to improve crashworthiness or show why accidents took place; such boxes did help Toyota convince federal regulators two years ago that most sudden acceleration complaints not tied to defects involved drivers mistaking the gas and brake pedals.

But the boxes -- typically installed out of sight -- remain a mystery to most car owners and a privacy concern to many. States have set a panoply of laws governing who can access the data stored in a black box; some allow law enforcement agencies to do so at an accident scene without a warrant, while others require some court oversight, but 37 states have no rules. The boxes themselves can't be turned off or disabled, and most require special software to access and read. In the Toyota cases, many probes were hampered because the black box data could only be read by Toyota engineers.

In a few high-profile crashes, black box data has been used to contradict the driver's explanation for a crash. When Massachusetts Lt. Gov. Timothy Murray wrecked his state-owned Ford Crown Victoria a year ago, he initially said he had been driving near the speed limit; the black box data revealed he was driving 100 mph without his seat belt on, likely because he fell asleep behind the wheel. Data from an SUV that crashed while carrying New Jersey Gov. Jon Corzine in 2007 showed it was doing 91 mph at the time of the wreck -- and that Corzine wasn't wearing a seat belt.

Several courts have allowed black box data as evidence in cases involving car crashes, but experts warn that the boxes are far from foolproof. Electrical surges have been known to erase or scramble the 15 data points modern boxes are required to collect, and the sensors can report faulty information. While federal law generally says the data belongs to car's owner, many insurance contracts allow insurance companies to gather the data after the crash. While automakers have asked NHTSA to clarify privacy concerns in any new rule, it will likely fall to Congress to decide who gets to talk to the spy in your dashboard.