What is a measure of safety effectiveness in transportation design?

The Crash Modification Factor (CMF) is a crucial measure of safety effectiveness in transportation design. It quantifies the expected change in crash frequency due to specific changes made in the roadway environment or traffic control measures. CMFs are derived from empirical studies and are used to assess the impact of design features on safety outcomes, allowing engineers and planners to evaluate the effectiveness of various interventions.

For example, if a certain roadway design change has a CMF of 0.8, it indicates a 20% reduction in crashes compared to the baseline condition, suggesting that the design is effectively improving safety. This enables transportation professionals to make data-driven decisions in their designs, prioritizing solutions that will lead to significant reductions in accidents.

While traffic volume, transportation incident rates, and vehicle occupancy rates provide useful context and information regarding roadway usage and potential congestion, they do not directly measure the effectiveness of safety measures implemented in transportation design. In contrast, the CMF specifically addresses how design modifications can enhance safety, making it the most relevant choice for assessing transportation design safety effectiveness.