Qualitative methods classify risks based on descriptions of frequency and severity criteria. Qualitative methods are subjective and usually assign relative risk rankings such as low, medium, high.
Quantitative methods are objective and place greater reliance on numerical data, statistics or records to “score” frequency of exposure, probability of occurrence and severity of impacts and calculate individual risk scores.
Risk assessments using either method should take full advantage of direct observations and records. In addition to understanding the consequences and costs of crashes, knowing how often crashes occur, when and where they happen, what the hazards were, and which vehicle, driver and journey characteristics were involved helps an organization conduct more informative risk assessments.
Risk assessments are forward-looking procedures seeking to anticipate risks and prevent MVIs. Many organizations simply don’t have enough data to use purely quantitative methods to assess road safety risks. Even if you use compiled industry data (see The Numbers section) or incident reports from other employers, it is difficult to gather enough reliable data to enable quantitative assessments.
As a result, evaluating road safety risks requires that assessors use the relevant statistics and values they can assemble along with their qualified estimate or informed best guess in a combination of qualitative and quantitative methods.
Sections below demonstrate two such hybrid methods.
- A Simple Risk Matrix is a 3 x 3 matrix that uses qualitative descriptions and comparative ranges of values to rank risks as high, medium or low.
- The Quantified Risk Scale has three risk variables and applies more precise qualitative criteria as well as specific values to calculate individual risk scores.