In the presence of labor market failures, workers may have financial incentives that penalize safety. This paper studies how failing to account for this incentive problem may result in ineffective safety interventions. We evaluate a policy introduced to curb excessive driving in trucking, an industry in which workplace accidents often generate a public safety externality. The policy inadvertently heightened the payoff for other unsafe driving practices, such as speeding, including during unsafe weather. Using data on 1.4 million truck crashes across the continental United States, we first show that truck crashes increase by 150 to 220 percent on days with icy weather. Leveraging the fact that the policy was binding for only a subset of truckers, we find that it led those truckers to experience 7 percent more crashes in icy conditions relative to a no-policy counterfactual. We then descriptively consider how alternative policy measures might affect safety and aggregate social welfare.