A group of major automakers accounting for more than half of U.S. auto sales will make automatic emergency braking standard on new U.S. vehicles in one of the industry’s biggest auto safety moves since it embraced technology to prevent rollovers more than a decade ago. The car makers, which accounted for 57 percent of car and light truck sales in the United States last year, said Friday they will work with regulators and the insurance industry to roll out collision avoiding braking technology across their lineups over the next few years.