The measures need to be selected based on evidence of the results they can be expected to produce. Detailed ex-ante assessment is employed in countries at the leading edge of achievement. In the United Kingdom, for example, targets for specific users or types of crash are based on ex-ante assessments. In the Netherlands, overall targets for reducing deaths and serious injuries are tightened periodically and the accompanying measures modelled to assess whether they will deliver the improvement required to meet the new target.