Improving the risk–risk trade-off method for use in safety project appraisal responses

The risk–risk trade-off method is a technique used to elicit the relative trade-off between changes in morbidity and mortality risks in stated preference surveys. The responses can be used to inform the (relative) values or weights that should be given to different accidents in cost–benefit analyses of road-safety projects that reduce the risk of death or injury. While the method has some distinct advantages over eliciting direct monetary measures of value, it is likely to suffer from similar problems that are found in other stated preference surveys, which might mitigate against its more widespread use. This study explores this issue, but shows that the estimates from a risk–risk trade-off study can be improved by employing a pre-survey learning experiment in which respondents make incentivised risky choices and also using a frame that focuses on the total risk or risks that respondents face, thereby broadening the toolkit available to measure preferences over road-safety interventions.