Cameras proliferate this data-driven age, replacing hazy recollections with clear digital images.

Starting on New Year's Day, 2011, this will be increasingly true on California's roadways when AB 1942 takes effect, legalizing the use of "video event recorders" in our cars.

For several years, police agencies have used these kinds of devices to document the conduct of officers during traffic stops. Going forward, vehicle owners can install them to create evidence of collisions and other hazardous driving conditions. As the state Senate's bill analysis describes the contraptions:

"Video event recorders for vehicles capture high definition videos, both of the front of the vehicle and the rear, using a dual camera device and record when an event occurs, including accidents or aggressive driving behavior. The videos are stored on internal memory together with other information such as G-force values, GPS coordinates, date, time, and more."

"The new law - authored by Assemblyman Nathan Fletcher, R-San Diego - authorizes the recorders' use for all California motorists, but was not intended for them, at least not initially. Professional drivers are likely to be the first to find themselves under the cameras.

In addition to the California State Sheriffs' Association, one of the legislation's chief backers was MV Transit, which operates buses and other passenger transportation services.

Supporters contend that the recorders decrease car accidents, in part because motorists drive differently when they are likely to be taped.

This is the logic behind the recorders' use in police squad cars.

"In the spirit of building public trust, the in-car camera recording provides an unbiased account of events that allow citizens and others to view what actually occurred during encounters that have been called into question," Lonnie J. Westphal, former chief of the Colorado State Patrol, wrote in Police Chief Magazine in 2004.

The measure passed both the state Assembly and Senate with hardly any opposition.

Only the American Civil Liberties Union put forward an argument against legalizing the recorders, centering on privacy. "While we understand the need for driver safety," the organization's position statement reads, "we do not believe that there has been sufficient evidence to demonstrate the need to allow the installation of cameras continuously trained on employees and other drivers."

Those installing the devices may not always like what the cameras record.

The clear evidence would document instances where the vehicle owner is liable, digital files that would probably be discoverable when car collisions land in court.