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, just click on the name of the calculation below, and the calculation will open in a new window.
Crash Query Calculations
Comparison Report Percent Change (Annualized)
Network Screening Calculations
Equivalent Property Damage Only (ePDO)
Predicted Crashes Per Mile (SPF)
Predictive Analysis Calculations
Expected Crashes Per Mile (EB)
Expected Excess Crash Rate (EB)
Expected Excess Crashes Per Mile (EB)
Level Of Service of Safety (LOSS)
Modified Level of Service of Safety (MLOSS)
Predicted Crashes Per Mile (SPF)
Predicted Excess Crash Rate (SPF)
Predicted Excess Crashes (SPF)
Predicted Excess Crashes Per Mile (SPF)
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 |
CMFs | Crash Modification Factor of Severity |
CR | Total number of crashes in the study period |
CR1 | Total number of crashes for time period 1 |
CR2 | Total number of crashes for time period 2 |
CRc1 | Crashes in Countermeasure 1 |
CRc12 | Crashes in Countermeasure 1&2 |
CRc13 | Crashes in Countermeasure 1&3 |
CRc123 | Crashes in Countermeasure 1, 2, & 3 |
CRf | Total number of crashes within the Crash Field |
CRfa | Total number of crashes per attribute within the Crash Field |
CRs | Crashes of Severity |
CR(k, a, b, c, o, u) | The total number of the corresponding K, A, B, C, O, and Unknown (U) crashes in the study period |
DR | Discount Rate |
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. |
O | Total number of Property Damage Only crashes in the study period |
SL | Service Life |
SW(k, a, b, c, o) | The Severity Weight of the corresponding K, A, B, C, O severity values |
TC | Cost of the treatment of the project |
Ty | 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) |
Comparison Report Percent Change (Annualized)
The expression used to determine the Annualized Percent Change in a comparison report is:
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)
Crash Report Percentages
The expression used to determine the percentages in Crash Reports is:
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:
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:
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:
Expected Crash Rate (EB)
[Also listed as: EB Expected Rate, Expectations Crashes Rate, Crashes Per Million Entering Vehicles]
The Expected Crash Rate is calculated by multiplying the Expected Crash Rate per Mile (ECPM) by the Rate Multiplier. This calculation utilizes Empirical Bayes to account for regression to the mean.
The expression used to determine the Expected Crash Rate is:
Expected Crash Ratio (EB)
[Also listed as EB Rato]
The Expected Crash Ratio is calculated by dividing the Crash Rate for the road segment by the Expected Crash Rate. This calculation utilizes Empirical Bayes to account for regression to the mean.
The expression used to determine the Expected Crash Ratio on a segment of roadway is:
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)
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.
Expected Excess Crash Rate (EB)
Expected Excess Crash Rate is calculated by multiplying the Expected Excess Crashes Per Mile by the Rate Multiplier. This calculation utilizes Empirical Bayes to account for regression to the mean.
The expression used to determine the Expected Excess Crash Rate is:
Expected Excess Crashes (EB)
[Also listed as: Expectation Excess, EB Excess]
Expected Excess Crashes are calculated by subtracting the crashes per year by the Expected Crashes (segment or intersection). This calculation utilizes Empirical Bayes to account for regression to the mean.
The expression used to determine the Expected Excess Crashes is:
(Note: for intersections, the segment length is defined as 1)
Expected Excess Crashes Per Mile (EB)
Expected Excess Crashes Per Mile is calculated by dividing the Expected Excess Crashes by the segment length. This calculation utilizes Empirical Bayes to account for regression to the mean.
The expression used to determine the Expected Excess Crashes Per Mile is:
Fatal Crashes
The Fatal Crashes Ranking in Network Screening displays the total number of observed Fatal Injury crashes during the screening date extents.
Level of Hazard
The level of Hazard (or LOH) is calculated by dividing the Expected Crash Rate by 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 Level of Hazard is:
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.
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.
Predicted Crash Rate (SPF)
[Also listed as: SPF Predicted Rate, Crashes Rate, Crashes Per Million Entering Vehicles]
The Predicted Crash Rate is calculated by multiplying the Predicted Crashes Per Mile (PCPM) by the Rate Multiplier. This calculation utilizes the state-provided SPF.
The expression used to determine the Predicted Crash Rate is:
Predicted Crash Ratio (SPF)
[Also listed as SPF Ratio]
The Predicted Crash Ratio is calculated by dividing the Crash Rate for the road segment by the Predicted Crash Rate. This calculation utilizes the state-provided SPF.
The expression used to determine the Predicted Crash Ratio on a segment of roadway is:
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)
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.
Predicted Excess Crash Rate (SPF)
Predicted Excess Crash Rate is calculated by multiplying the Predicted Excess Crashes Per Mile by the Rate Multiplier. This calculation utilizes the state-provided SPF.
The expression used to determine the Predicted Excess Crash Rate is:
Predicted Excess Crashes (SPF)
[Also listed as: Prediction Excess, SPF Excess]
Predicted Excess Crashes are calculated by subtracting the crashes per year from the Predicted Crashes (segment or intersection). This calculation utilizes the state-provided SPF.
The expression used to determine the Predicted Excess Crashes is:
(Note: for intersections, the segment length is defined as 1)
Predicted Excess Crashes Per Mile (SPF)
Predicted Excess Crashes Per Mile is calculated by dividing the Predicted Excess Crashes by the segment length. This calculation utilizes the state-provided SPF.
The expression used to determine the Predicted Excess Crashes Per Mile is:
PSI Potential
[Also listed as Potential for Safety Improvement]
Potential for Safety Improvement (PSI) Potential 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 Potential is:
PSI Potential Per Mile
Potential for Safety Improvement (PSI) Potential 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 Potential Per Mile is:
PSI Potential Rate
PSI Potential Rate is calculated by multiplying the PSI Potential 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 Potential Rate is:
Rate Multiplier
The Rate Multiplier is used in various calculations.
The expression used to determine the Rate Multiplier is:
