Planes have them. Trains have them. Some trucks do, too. And you may be driving around with one somewhere in your car and not know it.

A rule the National Highway Traffic Safety Administration proposed last month would blow the cover on "black boxes" in cars, standardizing by 2008 the kinds of information they collect and requiring the data be disclosed to those who own or lease the vehicles.

Also known by the auto industry and regulators as "event data recorders," or EDRs, these devices are connected to a vehicle's air-bag system and are capable of detecting many things, including the speed of the vehicle, whether the driver was wearing a seat belt at the time of a crash and how the brakes were applied.

Though some insurers, consumer groups, medical professionals and the National Transportation Safety Board have been pushing to make the boxes mandatory, the NHTSA proposal is limited to requiring automakers who install the devices to collect the same data in the same format -- 18 pieces of information in all.

The NHTSA says there are 30 million of the devices on the road and that up to 90 percent of new models will have the recorders. Under the proposal, carmakers would have to disclose in owners' manuals that the recorders have been installed and that they will record what happens in the seconds before and during a crash. They also would have to make it easier for researchers and crash investigators to access the recorded data, which can be difficult to mine.

John Hinch, a NHTSA safety engineer, said the agency is not interested in the information to determine who might be at fault in a crash -- as insurers or family lawyers might be -- but in the vehicle's speed and what happened in the split seconds before the crash. "We will have a better understanding of cause and effect and better rules in the future. EDR will allow us to build safer cars," Hinch said.

The leader in EDR technology is General Motors Corp. The car company, which has used the technology in a limited way since the 1970s, now equips all its models with the feature. Ford Motor Co. and Toyota have some of the capability. Chrysler has downplayed the recorders and said only a few of its models are collecting crash data.

Insurers, consumer groups and manufacturers have a variety of opinions about the usefulness of the data and how it should be used. Supporters of collecting the data think that safety research, car design and accident investigations would be enhanced by standardized information that one day could be centrally collected and analyzed.

Law enforcement officials regard it like DNA or a video camera in a bank -- it becomes a piece of valuable evidence. For example, an information dump from an event data recorder won a case for a prosecutor in Florida in 2003. It would have been hard to prove that the Pontiac Firebird was going 114 miles per hour without it.

"They are increasingly being used in litigation. It can be a key piece of evidence. This would revolutionize third-party claim settlements," said David Snyder, vice president of the American Insurance Association, which represents 400 auto insurance companies. "But their greatest value is in safety research."

Some carmakers are dubious about the rulemaking proposal. They predict that it will discourage the expanded use of event data recorders simply because of questions about who owns the data, the security of the information and the feelings consumers will have about its collection.

Robert S. Strassburger, vice president of vehicle safety and harmonization for the Alliance of Automobile Manufacturers, said the proposal would require significant changes for some manufacturers while others would have to invest in expanding their capability.

The automakers are likely to ask the agency to be definitive about the kind of information it needs for safety research. "It's got to be more than, 'It would be nice to have this information,'" Strassburger said.

The problematic issues are privacy and disclosure.

"If vehicle owners are not made aware of these systems, then potentially we have problems. By and large, the public is unaware they are in their vehicles," said Philip Haseltine, president of the Automotive Coalition for Traffic Safety, a group funded by the automakers. Consumers Union told the agency that it is concerned that insurers will require the use of EDR information as a condition of coverage in the future.

GM has responded to these concerns by highlighting the black box in owner's manuals and making related information easier to find. The car company said it gets the permission of owners or lessees before it downloads information. Courts can order the release of the information, and search warrants can be issued to obtain it.

Though the NHTSA proposal calls for disclosure in every owner's manual, Henry Jasny, general counsel for Advocates for Highway and Auto Safety, a consumer group, said there has to be more widespread publicity because few people consult the manual.

Debate in the states already is hot, particularly over who owns the information. California passed a law requiring disclosure that the device is in the vehicle and requiring the vehicle owner to give permission to download any of the data.

Nine other states, including Maryland and Virginia, are discussing legislation.