What are the risks associated with the use of a benefit - cost ratio when comparing safety countermeasures?

• A. It can understate the value of a project with significant benefits, if the costs are also high.
• B. It can overstate the value of a project with marginal benefits, if the costs of the project are extremely low.
• C. It may provide a false sense of objectivity for a project in which the benefits and / or costs are subjective or difficult to quantify.
• D. It guarantees objective results regardless of data quality.

Answer: (C)

The main idea is that a benefit-cost ratio relies on turning safety benefits and implementation costs into monetary values in order to compare options. The risk is that this can give a false sense of objectivity when the benefits and costs are subjective or hard to quantify. In road safety, many gains (like lives saved or injuries prevented) and some costs (such as disruption during rollout or long-term maintenance) are difficult to monetize precisely, and different valuation methods or data quality can produce very different numbers. Because the decision is boiled down to a single ratio, important uncertainties, distribution of impacts, and non-monetary effects can be hidden, leading to overconfidence in the result. To avoid this, it’s important to perform sensitivity analyses, consider net benefits in addition to the ratio, and account for non-monetized impacts alongside the monetary values.