Selective enforcement is most effective when...

Answer: C — Accident-causing violations are concentrated at a single location

Selective enforcement is most effective when accident-causing violations are concentrated at a single location. This is because targeted enforcement in areas where there is a high incidence of traffic violations or accidents allows law enforcement to address specific problems directly. By focusing resources and attention on a concentrated area of concern, officers can deter future violations, enhance safety, and reduce the likelihood of accidents. Concentrated enforcement efforts enable officers to establish a visible presence, which can deter potential violators who may rethink their behavior when they know that law enforcement is actively monitoring a high-risk area. Additionally, it allows for a more efficient use of resources, as officers can respond more quickly and effectively to incidents that may arise in that concentrated area. In contrast, when violations are dispersed across the city, it complicates enforcement efforts and dilutes the impact of any singular enforcement action taken by officers.