This research concerns interactions between actors on the car insurance market, and the corresponding influence of large decision makers (i.e., insurance companies and government) on each other and, eventually, on drivers’ incentives, and thus on road safety. We compare the public welfare-maximizing monopoly with a private profit-maximizing monopoly and competitive markets. The key stone of the analysis is the accident externalities that individual road users impose on one another via their presence on the road. Contrary to the case of private road optimization, where all externalities imposed by a customer remain internal to the private road supplier, this is not true in the context of accident externalities. In this paper we design optimal insurance premiums as well as manipulable tax rules, imposed on insurance companies in order to achieve the social optimum when agents anticipate the full impact of their actions on tax liabilities.