• December 2nd, 2017

From the Mountain Plains Consortium Report: Perception-Reaction Time (PRT) and deceleration rate are two key components in geometric design of highways and streets. Combined with a design speed, they determine the minimum required stopping sight distance (SSD). Current American Association of Highway Transportation Officials (AASHTO) SSD guidance related to PRT and deceleration rate are based on 90th percentile PRT and 10th percentile deceleration rate values from experiments that were completed in Texas in the mid-1990s (3).

Research Objectives:

  • Evaluating differences in perception-reaction times (PRT) and deceleration rates between crash and near-crash events
  • Assessing the correlation between PRT and deceleration rate
  • Determining if there is a causal relationship between PRT and deceleration rate (and what it is)
  • Developing predictive models for PRT and deceleration rate that can be used for roadway design and crash reconstruction

The analysis results indicated that crash events were associated with longer PRT values and lower deceleration rates. The Pearson correlation between PRT and deceleration rate was low. However, PRT was a causal factor of deceleration rate in both crash and near-crash events. In crash events, longer PRT values were associated with lower deceleration rates. In near-crash events, longer PRT values were associated with higher deceleration rates.

Regression models for crash reconstruction were estimated using panel and quantile regression methods. Applications of these models for both purposes are illustrated and discussed. The results for design applications are compared with existing AASHTO design guidance.

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