문장 속 that의 쓰임이 궁금해요

“The fatality rate in 2006 for motorists between 18 and 20, according to the National Highway Traffic Safety Administration, was more than double that for drivers over 70.”
여기서 that은 어떤 쓰임인가요?
관계대명사는 아닌 것 같은데 설명 부탁드립니다.