Transportation officials today issued a final rule that will require back-up cameras in cars under 10,000 pounds by May 2018.

"Safety is our highest priority, and we are committed to protecting the most vulnerable victims of backover accidents — our children and seniors," U.S. Transportation Secretary Anthony Foxx said in a statement. "As a father, I can only imagine how heart wrenching these types of accidents can be for families, but we hope that today's rule will serve as a significant step toward reducing these tragic accidents."

Vehicles - including buses and trucks - manufactured on or after May 1, 2018 must be equipped with rear-view cameras that let drivers see a 10-foot by 20-foot zone directly behind the vehicle. The system must also meet other requirements including image size, linger time (between 4 and 8 seconds), response time (2 seconds after a car is put into reverse), durability, and deactivation.

The National Highway Traffic Safety Administration (NHTSA) said there are an average of 210 deaths and 15,000 injuries a year caused by drivers backing over people behind their cars. About 31 percent of back-over fatalities affect kids 5 years and younger, while 26 percent impact those 70 years and older.

Back in September, safety advocates sued the Department of Transportation, arguing that the agency had dragged its feet on releasing federal standards for rear-view cameras in cars.

Rules were initially supposed to be in place by 2011, as required by the 2008 Cameron Gulbransen Kids Transportation Safety Act. President Bush approved the bill, which called for final rules within three years. A proposed rule was released by DOT in Dec. 2010, and a final draft was sent to the White House Office of Management and Budget (OMB) a year later. After three extensions, DOT in June 2013 withdrew its rule from OMB and pushed the deadline back to 2015, saying it needed more time to study the issue.

NHTSA said today that it "took time on this regulation to ensure that the policy was right and make the rule flexible and achievable."

As the agency noted, a number of car markers are already installing these cameras on their vehicles. "Including vehicles that already have systems installed, 58 to 69 lives are expected to be saved each year once the entire on-road vehicle fleet is equipped with rear visibility systems meeting the requirements of today's final rule," NHTSA said.