A decade and a half ago, research requested by Congress highlighted warning systems as a promising way to get more back-seat passengers to fasten their seat belts.
Over 10 years ago, safety advocacy groups formally asked the government to write rules requiring the warnings. They argued warnings could help save hundreds of lives each year, many of them children.
In 2012, Congress told regulators to get on it, asking for a rule within three years.
This fall, the National Highway Traffic Safety Administration put out an announcement saying they would think about it.