Complex sentence: In the United States in 2013, the National Highway Traffic Safety Administration (NHTSA) released a formal classification system, but abandoned this system when it adopted the SAE standard in September 2016.
Split into simpler sentences: In the United States, the National Highway Traffic Safety Administration (NHTSA) released in 2013 a formal classification system. The NHTSA abandoned this system when it adopted the SAE standard in September 2016.