A car crash and subsequent lane closure is affecting traffic on I-35W in southern Denton County on Monday morning. The Northlake Police Department, Flower Mound Fire Department and Denton County ESD No. 1 responded around 9:45 a.m. to the northbound lanes of I-35W, north of the FM 1171 exit, after a car crash and rollover, according to the ESD. One northbound lane is temporarily closed as police investigate and crews clean up the wreckage.