Below is a comprehensive list of the calculations used in the Numetric/AASHTOWare Safety applications. Each of these calculations references the terms identified in the Summary List of Terms below. To view a calculation, click on the name of the calculation below.
Crash Query Calculations
Network Screening Calculations
Predictive Analysis Calculations
Safety Analysis Calculations
Summary List of Terms
Term | Definition |
A | Total number of Suspected Serious Injury crashes in the study period |
ACR | Total number of Annual Crashes Reduced crashes in the study period |
B | Total number of Suspected Minor Injury crashes in the study period |
C | Total number of Possible Injury crashes in the study period |
CC | Crash costs based on severity type |
 | Crash Modification Factor of Severity |
CR | Total number of crashes in the study period |
 | Total number of crashes for time period 1 |
 | Total number of crashes for time period 2 |
 | Crashes in Countermeasure 1 |
 | Crashes in Countermeasure 1&2 |
 | Crashes in Countermeasure 1&3 |
 | Crashes in Countermeasure 1, 2, & 3 |
 | Total number of crashes within the Crash Field |
 | Total number of crashes per attribute within the Crash Field |
 | Crashes of Severity |
| The total number of the corresponding K, A, B, C, O, and Unknown (U) crashes in the study period |
DR | Discount Rate (Set to 3% by default) |
ECPM | Expected Crashes Per Mile (also referred to as EB Expectation Per mile) represents the yearly expected number of crashes per mile according to Empirical Bayes calculations.
Expected Crashes Per mile is calculated using the state configured SPFs and the observed crashes to determine the number of crashes expected, adjusted for regression to the mean. |
K | Total number of Fatal Injury crashes in the study period |
L | Length of the roadway segment in miles. This is a segment-level attribute. The segmentation approach for your agency is documented in your agency-specific article collection. |
M | Crash Multiplier. This value can be customized for each agency. |
PCPM | Predicted Crashes Per Mile represents the yearly predicted number of crashes per mile, as determined by the state-specific SPF for the segment type. |
O | Total number of Property Damage Only crashes in the study period |
SL | Service Life |
 | The Severity Weight of the corresponding K, A, B, C, O severity values |
TC | Cost of the treatment of the project |
 | Time, in years. Indicating the number of years of data (note, in the event that a fraction of a year is selected, the decimal equivalent will be used) |
U | Total number of Undefined Injury crashes in the study period |
V | Annual Average Daily Traffic (AADT) |
Calculations
Annual Crashes Reduced
The expression to determine Annual Crashes Reduced on an intersection or segment of roadway is:
Used in Safety Analysis.
Annual Severe Crashes Reduced
The expression to determine Annual Severe Crashes Reduced on an intersection or segment of roadway is:
Used in Safety Analysis.
Benefit
The expression to determine the Benefit on an intersection or segment of roadway for a single severity is:
Used in Safety Analysis.
Benefit Cost Ratio
The expression to determine Benefit Cost Ratio on an intersection or segment of roadway is:
Used in Safety Analysis.
Comparison Report Percent Change (Annualized)
The expression used to determine the Annualized Percent Change in a comparison report is:
Used in Crash Query.
Crash Rate
The Crash Rate is calculated by multiplying the Crashes Per Mile by the Rate Multiplier.
The expression used to determine the Crash Rate on a segment of roadway is:
(Note for intersections, the Segment Length is defined as 1, and the Volume used is the Total Entering Vehicles (TEV), which is the sum of the major and minor legs of the intersection)
Used in Network Screening.
Crash Report Percentages
The expression used to determine the percentages in Crash Reports is:
Used in Crash Query.
Crashes
The Crashes ranking displays the total number of observed crashes in the segment or intersection during the screening date extents, regardless of severity (including Unknown injury crashes).
The expression used to determine Crashes is:
Used in Network Screening and Predictive Analysis.
Crashes Per Mile
Crashes Per Mile is calculated by dividing Crashes Per Year by the segment length.
The expression used to determine Crashes Per Mile on a segment of roadway is:
Used in Network Screening.
Equivalent Property Damage Only (ePDO)
Equivalent Property Damage Only (ePDO) is used to compare crash severity types among each other. Each severity is assigned a Severity Weight to indicate the number of property damage only crashes would be equivalent to a single crash of that severity (e.g. one “B Injury” crash could be considered equivalent to 19.1 “O Injury” crashes). These Severity Weights are determined by each agency.
The expression used to determine the ePDO on a segment or intersection is:
Used in Network Screening.
Expected Crashes (EB)
[Also listed as: EB Expectation, Expected Crashes]
Expected Crashes determines the number of crashes per year expected for the given segment or intersection according to the Empirical Bayes regression to the mean.
The expression used to determine the Expected Crashes is:
(Note: for intersections, the segment length is defined as 1)
Used in Network Screening and Predictive Analysis.
Expected Crashes Per Mile (EB)
[Also listed as: ECPM, EB Expectation Per Mile, Crashes Per Mile]
Expected Crashes Per Mile (ECPM) represents the yearly expected number of crashes per mile according to Empirical Bayes calculations.
Expected Crashes Per mile is calculated using the state configured SPFs and the observed crashes to determine the number of crashes expected, adjusted for regression to the mean.
Used in Predictive Analysis.
Fatal Crashes
The Fatal Crashes Ranking in Network Screening displays the total number of observed Fatal Injury crashes during the screening date extents.
Used in Network Screening.
Level Of Service of Safety (LOSS)
Level Of Service of Safety compares the observed crash frequency and/or severity to the mean value predicted for the reference population using a state-provided SPF. The difference between the two values yields a performance measure that ranges between LOSS I and LOSS IV, with LOSS I indicating a low potential for crash reduction and LOSS IV indicating a high potential for crash reduction.
Used in Predictive Analysis.
Modified Level of Service of Safety (MLOSS)
Modified Level Of Service of Safety compares the Empirical Bayes modified crash frequency and/or severity to the mean value predicted for the reference population using a state-provided SPF. The difference between the two values yields a performance measure that ranges between LOSS I and LOSS IV, with LOSS I indicating a low potential for crash reduction and LOSS IV indicating a high potential for crash reduction.
Used in Predictive Analysis.
Predicted Crashes (SPF)
[Also listed as: SPF Prediction, Predicted Crashes]
Predicted Crashes determines the number of crashes per year predicted for the given segment or intersection as determined by the state-specific SPF for the segment or intersection type.
The expression used to determine Predicted Crashes is:
(Note: for intersections, the segment length is defined as 1)
Used in Network Screening and Predictive Analysis.
Predicted Crashes Per Mile (SPF)
[Also listed as: SPF Prediction Per Mile, Crashes Per Mile]
Predicted Crashes Per Mile represents the yearly predicted number of crashes per mile, as determined by the state-specific SPF for the segment type.
Used in Network Screening and Predictive Analysis.
PSI
[Also listed as Potential for Safety Improvement]
Potential for Safety Improvement (PSI) is calculated by subtracting the Expected Crash Rate from the Predicted Crash Rate. This calculation utilizes both Empirical Bayes to account for the regression to the mean, as well as the state-provided SPF.
The expression used to determine the PSI is:
Used in Network Screening and Predictive Analysis.
PSI Per Mile
Potential for Safety Improvement (PSI) Per Mile is calculated by dividing the PSI by the segment length. This calculation utilizes both Empirical Bayes to account for the regression to the mean, as well as the state-provided SPF.
The expression used to determine the PSI Per Mile is:
Used in Network Screening and Predictive Analysis.
PSI Rate
PSI Rate is calculated by multiplying the PSI Per Mile by the Rate Multiplier. This calculation utilizes both Empirical Bayes to account for the regression to the mean, as well as the state-provided SPF.
The expression used to determine the PSI Rate is:
Used in Network Screening and Predictive Analysis.
Rate Multiplier
The Rate Multiplier is used in various calculations.
The expression used to determine the Rate Multiplier is:
Used in Network Screening and Predictive Analysis.
Unique Benefit
The expression to determine the Unique Benefit on an intersection or segment of roadway is:
Used in Safety Analysis.
Overlapping CMFs
Find the Overlapping CMF Calculations here.