Lois Cooper was the first female African American transportation engineer to be hired in the Engineering Department at the Division of Highways, now known as California Department of Transportation (Caltrans), in 1953. She was also the first African American woman in California to pass the Professional Engineers (PE) License Exam.
She was a part of several significant projects during her career, including the I-105 Century Freeway, the San Diego Freeway, the Long Beach Freeway, the San Gabriel River Freeway, and the Riverside Freeway. She was also the first female director of the First Diamond Lane, the predecessor to carpool lanes. In addition to her career achievements, Cooper participated in the Los Angeles Council of Black Professional Engineers, visiting students and advocating for math and science in schools.