A National Highway Traffic Safety Administration study, withheld from the public since 2003 and finally released Tuesday, found that hands-free mobile technology presents as much of a safety hazard as handheld phones.

Two advocacy groups, Public Citizen and the Center for Auto Safety, obtained the data, which was published on the New York Times web site.

"Specifically, the experimental data reveal observable degradations in driver behavior and performance and changes in risk-taking and decision-making behaviors when using both hand-held and hands-free mobile phones," the study said.

The two safety groups expressed concern over the information that was kept secret for six years, saying that the government has endangered lives. In addition, many cities and states have approved laws requiring drivers to opt for hands-free phones, rather than handheld.

"By withholding this data, the National Highway Traffic Safety Administration led consumers to believe that it was safe to talk on their cell phones while driving if they kept both hands on the wheel," a Public Citizen press release said.

The study points to the danger of simple conversation, which can disrupt attentive scanning and information processing of the visual scene. The research says this conversation can contribute to extra demand on the driver, which can cause late detection, reduced situation awareness and reduced margin of safety. The report also finds that drivers using hands-free features talk on the phone with greater frequency and for longer intervals.

The Center for Auto Safety is petitioning the government to limit the availability of two-way communication features through in-vehicle systems while the vehicle is in motion, based on information in the report. The center is also urging the NHTSA to support state programs designed to limit use of all cell phones devices, hands-free and handheld, while driving.

The Center for Auto Safety obtained the study after suing the agency, which did not grant its Freedom of Information Act request in 2008.

To access the study, click here.