Rethinking traffic safety: the case for reducing kinetic energy exposure, not just speed

This study extends beyond traditional speed and conflict management approaches to explore the role of kinetic energy exposure in shaping road safety outcomes.

We examined the associations between exposure-based metrics (ie, mode share, vehicle miles travelled (VMT) and commute time) and fatality rates (ie, overall, vehicle occupant, pedestrian and bicyclist) by analysing 227 urban areas across 45 US states, controlling for other transportation and socioeconomic covariates. We used linear mixed-effects models to account for unobserved heterogeneity at the state level.

The results indicate that exposure plays a central role in shaping traffic fatality rates. Overall, measures of auto-dominance - particularly automobile mode share and VMT - are most strongly associated with higher fatality rates. When examining specific road users, time spent in the transport system emerges as a key predictor across modes. However, mode share appears more strongly associated with safety outcomes for vulnerable road users (ie, pedestrians and cyclists) whereas VMT is more strongly associated with motor vehicle occupant fatality rates. Notably, exposure-related factors remain strong and significant even for individuals travelling in cars, underscoring that increased system exposure elevates risk across all user types.

Our findings also reinforce the association between socioeconomic and demographic conditions and safety outcomes. However, in addition to longstanding strategies focused on kinetic energy severity (eg, speed management) and kinetic energy likelihood (eg, conflict management), our results suggest that reducing fatality rates requires reducing overall kinetic energy exposure. Providing viable modal alternatives and designing communities that enable shorter travel distances and less time spent in the transportation system may be critical components of a comprehensive road safety strategy.