Accident SEA
Accident Involvement Indicator (AII)
Accident Involvement Measure (AIM)
Recordable Accident Indicator (RAI)
Recordable Accident Rate (RAR)
Accident SEA Value

ACCIDENT SEA

The Accident SEA Value reflects a carrier's crash experience relative to its peers. The Accident SEA Value is based on the Accident Involvement Indicator (AII) and the Recordable Accident Indicator (RAI). The AII uses measures derived from state-reported crash data normalized by power unit data from the Motor Carrier Census. The RAI uses measures based on recordable crash and annual vehicle-miles traveled (VMT) data gathered at the most recent compliance review. The sections that follow present the specific computations for each measure, indicator, and the Accident SEA Value. Figure 3-1 shows the computational hierarchy used to calculate an Accident SEA Value.
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Figure 3-1. Accident SEA Value Computational Hierarchy

Accident Involvement Indicator (AII)

SafeStat uses the state-reported crash data and Motor Carrier Census power unit (trucks, tractors, hazardous material tank trucks, motor coaches, and school buses) data to calculate the Accident Involvement Measure (AIM) for all carriers. SafeStat uses only vehicles involved in crashes that have occurred within the last 30 months and time weights the data to give more relevance to recent crashes than to older crashes. It also weights individual crashes based upon the consequences of the crash (i.e., vehicle towed, injury, fatality, and release of hazardous material). SafeStat then normalizes this weighted crash information by the number of power units to obtain the AIM. Carriers with similar numbers of state-reported crashes are grouped, compared to one another by their AIMs, and ranked on a percentile basis. SafeStat assigns a percentile number (from 0-100) to the AII of each carrier, based on that rank. A carrier must have two or more crashes to have the potential to receive a deficient AII, i.e., 75 or higher.

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State-Reported (Reportable) Crash Data

States provide a crash report for each commercial motor vehicle involved in a crash that meets the reportable crash standard. A reportable crash involves a vehicle being towed from the scene, or an injury or fatality. Each crash report is counted as a crash by SafeStat. SafeStat uses the following data elements from the reportable crash data to calculate the carrier's AII:

Date of the crash
Injuries
Fatalities
Release of Hazardous Material (HM)

Census Power Unit Data

SafeStat computes the AII using state-reported crash data, which are normalized by the number of owned, term-leased, and trip-leased power units (trucks, tractors, hazardous material tank trucks, motor coaches, and school buses) contained in the Census data. The primary source of power unit information in the Census is Forms MCS-150 and MCS-151. Carriers are required to update their MCS-150 information biennially. When the number of power units for a carrier is suspect, specific state/federal organizations are notified to obtain the most accurate value.

Accident Involvement Measure (AIM)

SafeStat uses the reportable crash data that fall within three time windows. It time weights the data to give more relevance to recent crash involvement than to older crash involvement. It also weights individual crashes based upon the consequences of the crash (i.e., vehicle towed, injury, fatality, and release of hazardous material). SafeStat combines these two weighting aspects into a quantity called the Total Consequence/Time Weighted Crashes (TCTWC). SafeStat calculates the AIM by dividing the TCTWC by the average number of power units (PU) for the carrier to normalize the measure. The basic equation for the AIM is shown below. The steps that follow the equation detail SafeStat's calculation of the AIM.

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AIM = TCTWC / PU

A. Begin to compute the TCTWC by aggregating each carrier's reportable crash data into three time periods based on the age of each crash: 0 to 6 months, 7 to 18 months, and 19 to 30 months.

B. Within each time period, weight each crash for severity by assigning a severity score of 1 for crashes which involved a vehicle being towed (but no injuries), and 2 for crashes which involved injury or fatality. Add 1 to the severity score if a carrier vehicle released hazardous materials.

Severity Score (Towed, Injury and Fatality + HM Releases)

C. Within each time period, sum the severity scores to get a total crash severity score for the time period:

Total Severity Scores to get a Total Crash Severity Score for that time period

D. Time weight the severity scores for the three time periods so that the most recent crashes receive the most weight, then sum the weighted scores for all three periods to produce the Total Consequence/Time-Weighted Crashes (TCTWC).

Total Consequence/Time-Weighted Crashes (TCTWC)

E. Calculate the average number of PUs over 30-month time frame by determining the number of PUs at the end of each of the three time periods.

Calculate the average number of PUs over 30-month time frame by

deterblackSMTextng the number of PUs at the end of each of the three time periods.

F. Compute AIM by dividing the TCTWC by the average number of PUs (trucks and buses owned, term-leased and trip-leased).

Compute AIM by dividing the TCTWC by the number of PUs (trucks and buses owned
and term-leased)

Calculation of the Accident Involvement Indicator (AII)

SafeStat uses the Accident Involvement Measure (AIM) to calculate the Accident Involvement Indicator (AII). The following steps detail SafeStat’s calculation of AII.

A. Determine the total number of each carrier's vehicles involved in crashes over the past 30 months (no time or severity weighting), and place each carrier into one of the groups below:

*Group*	*Number of Vehicles Involved in State-Reported Crashes*
0	0
1	1
2	2-3
3	4-8
4	9-20
5	21-88
6	89+

B. For Group 0: Assign an AII of 0.

For Group 1: Insufficient information to calculate a percentile ranking. No AII assigned.

For Groups 2 through 6: within each group, rank all the carriers' AIM values in ascending order. Transform the ranked values into percentiles from the 0 percentile (representing the lowest AIM) to the 100th percentile (representing the highest AIM). Assign the percentile value to the AII. If a carrier has no crashes within the past 24 months, the AII will be capped at 74.

Recordable Accident Indicator (RAI)

SafeStat uses recordable crash and vehicle-miles-traveled (VMT) data gathered during compliance reviews to calculate the Recordable Accident Rate (RAR) for all carriers that have had compliance reviews within the past 12 months. SafeStat takes the number of recordable crashes and normalizes it by VMT to obtain an RAR. Carriers with similar numbers of recordable crashes are grouped, compared to one another by their crash rates, and ranked on a percentile basis. SafeStat assigns a percentile number (from 0-100) to each carrier based on that rank. A carrier must have two or more crashes to potentially receive a deficient RAI, i.e., 75 or higher.

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Compliance Review Data

The data items used in assessing recordable crashes are the following:

Date of the review
Number of recordable crashes (RC) within 12 months prior to the review
Total number of vehicle miles traveled (VMT) by a carrier within 12 months prior to the review

Calculation of the Recordable Accident Rate (RAR) Measure

SafeStat uses the recordable crash data described above from the most recent review of a carrier that was performed within the last 12 months to produce a measure called the Recordable Accident Rate (RAR). The RAR is computed by dividing the total number of recordable crashes (RC) by the number of annual vehicle miles traveled (VMT) and then multiplying this quotient by a convenient constant (in this case, 1,000,000) to establish a manageable RAR size. The basic equation for RAR follows. The steps following the equation detail SafeStat's calculation of the RAR.

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RAR =	1,000,000 x RC
	VMT

A. Identify all carriers whose most recent compliance review was performed within the last 12 months. B. Compute the RAR according to the following formula:

Compute RAR (RAR = 1,000,000 x RC / VMT)

Calculation of the Recordable Accident Indicator (RAI)

SafeStat calculates the Recordable Accident Indicator (RAI) by ranking the RAR values and transforming them into percentiles. The following steps detail SafeStat's calculations.

A. Determine the total number of crashes for each carrier (no time or severity weighting), and place each carrier into one of the groups below:

*Group*	*Number of Recordable Crashes*
0	0
1	1
2	2-4
3	5-19
4	20+

B. For Group 0: Assign a RAI of 0.

For Group 1: Insufficient information to calculate a percentile ranking. No RAI is assigned.

For Groups 2 through 4: within each group, rank all the carriers' RAR values in ascending order. Transform the ranked values into percentiles from the 0 percentile (representing the lowest RAR) to the 100th percentile (representing the highest RAR). Assign the percentile value to the RAR.

Calculation of the Accident SEA Value

The Accident SEA Value establishes the carrier's safety status concerning its crash history. SafeStat uses the Accident Involvement Indicator (AII), the Recordable Accident Indicator (RAI), and any state-reported crashes that have occurred since the CR was performed to calculate the Accident SEA Value. Several possible cases exist in determining the Accident SEA Value. SafeStat determines which case exists for each carrier and calculates the Accident SEA Value accordingly.

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Case 1: If no CRs were conducted in the past 12 months, AII is assigned to the Accident SEA Value. (If the AII was not assigned in the case of only one crash, then the Accident SEA is also not assigned a value).

Case 2: If a CR was conducted within the past 12 months and no new state-reported crashes have occurred since the CR was conducted, then assign the RAI to the Accident SEA Value. (If the RAI was not assigned in the case of only one crash, then the Accident SEA is also not assigned a value).

Case 3: If a CR was conducted within the past 12 months and a new state-reported crash has occurred since the CR was conducted, then assign the higher value of AII and RAI to the Accident SEA. (In the unique case where the RAI is based on 0 or 1 recordable crash, and the AII is not assigned based on 1 state-reported crash, the Accident SEA is not assigned a value).

Accident SEA Value = Highest of (AII, RAI)