During the last decade much progress has been made in defining & measuring the external costs of transport. As the cost of tolling equipment falls, the set of realistic policy options to internalise these externalities will continue to grow. This will determine the research and policy agenda. We make three points. Firstly, empirical work is still necessary to better identify marginal external costs, including congestion, accident and environmental costs. Secondly, any assessment of policy options should treat externalities simultaneously. The use of pricing instruments and emissions standards are discussed within this framework. Thirdly, we emphasise the role of government. Designing the optimal road-pricing institutions requires consideration of horizontal and vertical tax competition, while double-dividend arguments are central to the question of securing public support.