Sarah Seo is the author of Policing the Open Road: How Cars Transformed American Freedom. She explains how traffic enforcement fundamentally changed Fourth Amendment jurisprudence in the 20th century. Namely, it vastly expanded police discretion, creating the law enforcement regime that has presided over numerous high profile killings of unarmed black drivers by police in recent years. We rethink that regime. Then, we take a turn to ask what the 20th century’s major technological disruption (cars) can teach us about how we in the 21st century can respond to new disruptive technologies like big data.