In February 2008, President George W. Bush signed into law a bill that essentially required that new cars sold in the United States be equipped with rearview cameras to prevent back-up accidents.

The measure would save about 100 lives per year, many of them children, and prevent 7,000 injuries, according to the Transportation Department. It would cost between $58 and $203 per vehicle.

More than five years later, the law has yet to take effect.

“It’s one of those rules that is so obvious it just should be done,” said Joan Claybrook, former administrator of the National Highway Traffic Safety Administration and president emeritus of Public Citizen, a consumer group. “But it hasn’t been.”

A coalition of safety groups — Consumers Union, Advocates for Highway and Auto Safety, and Kids and Cars — is expected to file a lawsuit Wednesday asking a judge to force the federal government to implement the requirement.

The law does not explicitly require that cars be equipped with rearview cameras; it calls for expanding the federal requirements for rear visibility in vehicles. Given current technology, according to the Transportation Department, that means cameras.

Automakers oppose the rule, saying consumers should be given a choice of which safety features to pay for — and that they already have an option regarding rearview cameras. About 45 percent of 2012 models had back-up cameras as a standard feature, according to automotive Web site

“Consumers should decide how they want to spend their safety dollars,” said Gloria Bergquist, vice president of the Auto Alliance, a lobbying group. “Let the marketplace decide.”

One of the expected plaintiffs is Greg Gulbransen, a Syosset, N.Y., pediatrician whose son Cameron was killed by an SUV that was backing up in 2002.

“I was the driver of the car that terrible night, and although I used both side-view mirrors and the rear view mirror and looked over my shoulder in an attempt to avoid hitting anything, I could not see that Cameron had run into the driveway because he was too small for me to see him behind my vehicle,” he said in a statement.

Cost has always been a central part of the debate, and advocates say that the issue has led to delays in implementation.

In issuing a proposed rule in December 2010, the Transportation Department estimated the overall cost to be between $1.9 billion and $2.7 billion.

“These costs are admittedly substantial,” the Department of Transportation notice said. Nonetheless, officials concluded tentatively that “the benefits justify the costs.”

The department did not comment on the expected lawsuit, but a spokesman noted that it had recently added back-up cameras to its list of recommended safety features.

“As we’ve seen with other features in the past, adding rearview video systems to our list of recommended safety features will encourage both automakers and consumers to consider more vehicles that offer this important technology,” U.S. Transportation Secretary Anthony Foxx said in a statement.

“It’s tragic every time a young child is killed or injured this way,” Sen. John D. Rockefeller IV (D-W.Va.), chairman of the Senate commerce committee, said in a statement. “When the experts tell me that installing rear cameras in cars could save the lives of hundreds of young children and prevent thousands of heartbreaking injuries, I want action. I’ve supported this safety rule for a long time. I continue to believe the Administration needs to move forward with this common sense safety measure.”