6.1.4.2 HSM Part C Predictive Method
The purpose of the HSM Part C predictive method is to provide a structured method for determining predicted or expected average crash frequencies for both existing and proposed future conditions of a roadway network, facility, or individual site. A detailed introduction into the HSM Part C Predictive Method is provided in
Chapter 5, Section 5.3
.Alternative | CMF Description | CMF ID | CMF Value | Star Rating |
|---|---|---|---|---|
Alternative #1 – Pedestrian Hybrid Beacon | Install pedestrian hybrid beacon (PHB) with advanced yield or stop markings and signs | 9021 | 0.432 | 4 Star |
Alternative #2 – Raised Median | Install raised median with marked crosswalk (uncontrolled) | 175 | 0.54 | 3 Star |
Alternative #3 – Raised pedestrian crosswalks | Install raised pedestrian crosswalks | 136 | 0.55 | 3 Star |
Alternative #4 – Rectangular Rapid Flashing Beacon (RRFB) | Install RRFB | 9024 | 0.526 | 3 Star |
There are four analysis approaches for applying the HSM Part C predictive method to estimate the safety effectiveness of proposed projects or alternatives. Not all analysis methods have the same order of reliability when investigating the results of the potential safety impacts of proposed improvements or alternatives. It is important for practitioners to determine which analysis method is most applicable for the given analysis scenario. presents a flowchart for where the HSM Part C predictive method analysis falls within the future conditions analysis. The following are the four HSM Part C predictive method analysis approaches in order of highest to lowest predictive reliability:
- Approach #1 – Apply the Part C predictive method to estimate the average crash frequency for both the existing and proposed conditions.
- Approach #2 – Apply the Part C predictive method to estimate the average crash frequency for the existing conditions. Apply the appropriate CMF(s) related to the proposed condition to the existing condition results to estimate the safety performance of the proposed condition. Approach 2 is typically applied when the proposed conditions do not apply directly to a predictive model located within the HSM. The CMF located on the CMF Clearinghouse needs to be applied to the results from the predictive method for the existing conditions to generate predictive results for the proposed conditions.
- Approach #3 – Use a SPF developed outside of the HSM to estimate the average crash frequency for the existing conditions, then apply the appropriate CMF(s) related to the proposed condition to the existing condition results to estimate the safety performance of the proposed condition.
- Approach #4 – Use historical crash data to estimate the average crash frequency of the existing condition and then apply the appropriate CMF(s) related to the proposed condition to the historical crash data to estimate the average crash frequency for the proposed condition.
The basic analysis steps when performing HSM Part C predictive method analysis are as follows:
- Determine the safety study area based on project type, complexity, and impact of proposed improvements;
- Determine the analysis years;
- Determine which of the four approaches is the most appropriate;
- Apply the HSM predictive method 18- step process, where applicable;
- Determine appropriate CMF(s), where appropriate;
- Document analysis methodology, approach, and assumptions; and
- Summarize and document analysis results