sentences:  These roads are maintained by the Harris County Toll Road Authority, and add approximately of highways to the overall Harris County highway system.There are four interstates located within Harris County.They consist of three major interstates (Interstate 10 (I-10), known as the Katy Freeway and the East Freeway, Interstate 45 (I-45), known as the Gulf Freeway and the North Freeway, and Interstate 69 (I-69), known as the Southwest Freeway and the Eastex Freeway) and one Auxiliary Interstate (Interstate 610 (I-610), known as "The Loop").