The 2000s were a big era for improved safety. The NHSTA began studying and testing a wider variety of different crashes events and used ATDs (crash test dummies) designed to simulate women and children. Side-impact airbags became mandatory equipment in the USA in 2007 and electronic stability control in 2008.

It's not something people realize because they think car safety improvements slowed/stopped once airbags became widespread. But really, the mid 2000s are when cars began to get very safe. By 2011, the NHSTA had to make their star rating system much more strict because nearly every car had a achieved a five star rating.