In the spring of 2018, Abena Marfo left her home in Garland and drove to the leafy campus of Southern Methodist University, a private school located in the upscale Dallas enclave of University Park. She was both nervous and excited to tour campus and meet professors who might be teaching her in the fall, when she would start at SMU as a freshman. But as she drove through campus, she saw the flash of police lights in her rearview mirror. The $180 ticket for failing to yield on a left turn stung...