When Timothy P. Murray crashed his government-issued Ford Crown Victoria in 2011, he was fortunate, as car accidents go. Mr. Murray, then the lieutenant governor of Massachusetts, was not seriously hurt, and he told the police he was wearing a seat belt and was not speeding.

But a different story soon emerged. Mr. Murray was driving over 100 miles an hour and was not wearing a seat belt, according to the computer in his car that tracks certain actions. He was given a $555 ticket; he later said he had fallen asleep.

The case put Mr. Murray at the center of a growing debate over a little-known but increasingly important piece of equipment buried deep inside a car: the event data recorder, more commonly known as the black box.

About 96 percent of all new vehicles sold in the United States have the boxes, and in September 2014, if the National Highway Traffic Safety Administration has its way, all will have them.

The boxes have long been used by car companies to assess the performance of their vehicles. But data stored in the devices is increasingly being used to identify safety problems in cars and as evidence in traffic accidents and criminal cases. And the trove of data inside the boxes has raised privacy concerns, including questions about who owns the information, and what it can be used for, even as critics have raised questions about its reliability.

To federal regulators, law enforcement authorities and insurance companies, the data is an indispensable tool to investigate crashes.

The black boxes “provide critical safety information that might not otherwise be available to N.H.T.S.A. to evaluate what happened during a crash — and what future steps could be taken to save lives and prevent injuries,” David L. Strickland, the safety agency’s administrator, said in a statement.

But to consumer advocates, the data is only the latest example of governments and companies having too much access to private information. Once gathered, they say, the data can be used against car owners, to find fault in accidents or in criminal investigations.

“These cars are equipped with computers that collect massive amounts of data,” said Khaliah Barnes of the Electronic Privacy Information Center, a Washington-based consumer group. “Without protections, it can lead to all kinds of abuse.”

What’s more, consumer advocates say, government officials have yet to provide consistent guidelines on how the data should be used.

“There are no clear standards that say, this is a permissible use of the data and this is not,” Ms. Barnes said.

Fourteen states, including New York, have passed laws that say that, even though the data belongs to the vehicle’s owner, law enforcement officials and those involved in civil litigation can gain access to the black boxes with a court order.

In these states, lawyers may subpoena the data for criminal investigations and civil lawsuits, making the information accessible to third parties, including law enforcement or insurance companies that could cancel a driver’s policy or raise a driver’s premium based on the recorder’s data.

In Mr. Murray’s case, a court order was not required to release the data to investigators. Massachusetts is not among the states to pass a law governing access to the data. Asked about the case, Mr. Murray, who did not contest the ticket and who resigned as lieutenant governor in June to become head of the Chamber of Commerce in Worcester, Mass., declined to comment.

Current regulations require that the presence of the black box be disclosed in the owner’s manual. But the vast majority of drivers who do not read the manual thoroughly may not know that their vehicle can capture and record their speed, brake position, seat belt use and other data each time they get behind the wheel.

Unlike the black boxes on airplanes, which continually record data including audio and system performance, the cars’ recorders capture only the few seconds surrounding a crash or air bag deployment. A separate device extracts the data, which is then analyzed through computer software.

The Alliance of Automobile Manufacturers, a Washington-based trade association that represents 12 automakers including General Motors and Chrysler, said it supported the mandate because the recorders helped to monitor passenger safety.

“Event data recorders help our engineers and researchers understand how cars perform in the real world, and one of our priorities for E.D.R.’s continues to be preserving consumer privacy,” said Wade Newton, a spokesman for the trade association. “Automakers don’t access E.D.R. data without consumer permission, and we believe that any government requirements to install E.D.R.’s on all vehicles must include steps to protect consumer privacy.”

Beyond the privacy concerns, though, critics have questioned the data’s reliability.

In 2009, Anthony Niemeyer died after crashing a rented Ford Focus in Las Vegas. His widow, Kathryn, sued both Ford Motor and Hertz, contending that the air bag system failed to deploy.

The black box, however, derailed Ms. Niemeyer’s assertion that her husband had been traveling fast enough for the air bag to deploy.

Though Ms. Niemeyer lost the suit last year, her lawyer, Daniel T. Ryan of St. Louis, was successful in excluding the black box data as evidence on the grounds that the device is not fully reliable. The judge in the case ruled that because an engineer working on behalf of the defense retrieved the data, the plaintiffs, who maintained there were errors, had no way to independently verify it.

“It’s data that has not been shown to be absolutely reliable,” Mr. Ryan said. “It’s not black and white.”

The origins of black boxes, which are the size of about two decks of cards and are situated under the center console, date to the 1990 model year, when General Motors introduced them to conduct quality studies. Since then, their use and the scope of the data they collect has expanded.

The lack of standardization among manufacturers has made it difficult to extract the data, most notably during the investigations into the crashes caused by sudden, unintended acceleration in some Toyota vehicles.

Until recently, crash investigators needed an automaker’s proprietary reader as well as the expertise to analyze the data. The safety administration’s regulations will help enable universal access to the data by using a commercially available tool. At the same time, police departments are receiving training on the new regulations. In Romulus, N.Y., last week, the Collision Safety Institute, a consultancy in San Diego, helped teach New York State Police investigators how to read the devices.

But privacy advocates have expressed concern that the data collected will only grow to include a wider time frame and other elements like GPS and location-based services.

“The rabbit hole goes very deep when talking about this stuff,” said Thomas Kowalick, an expert in event data recorders and a former co-chairman of the federal committee that set the standard for black boxes.

Today, the boxes have spawned a cottage industry for YouTube videos on how to expunge the data. And Mr. Kowalick, seeing an opportunity, invented a device that safeguards access to in-vehicle electronics networks. It is controlled by the vehicle’s owner with a key and is useful in the event of theft, he said.

“For most of the 100-year history of the car, it used to be ‘he said, she said,’ ” Mr. Kowalick said. “That’s no longer going to be the way.”