The relationship between deregulation in the trucking industry and highway safety is an important economic and social issue. Analyses thus far have concentrated on the relationship between the downward pressure imposed on freight rates by deregulation and total safety investment by firms. Two issues which have been ignored are the effects that deregulation had on route carriage restrictions and total firm mileage. We show that the inclusion of these factors yields a model in which the relationship between motor carrier deregulation and highway safety is dependent upon the relative effects of all three factors. Estimation of the model using accident data implies that trucking deregulation did not deteriorate highway safety and may have actually improved it.